Sunday
November 23, 2014

Homework Help: science (chem)

Posted by christina on Monday, July 2, 2007 at 7:13pm.

Does EDTA react with light?
I forgot to cover a dilute bottle of EDTA (about 0.01M) and was wondering if that would have any affect on the solution

I don't think so. I have used EDTA many times and never covered it or used a tinted container.

okay =)

i posted an answer to the last post on the solution being cooled topic ...pg 4

Good reminder since I usually don't look after a couple of pages. I recopied your post here so it will be more convenient.

I was referring to just plain tap water in a beaker and just floating the flask in there.

Right. The plain tap water is good.

When I made the NaOH solution, I boiled the water again and left it in the bottle with the CO2 absorber and put that into a cold water bath, then the problems startedÖ.First I didnít have enough boiled water and I found that out when I put the water + 5ml 50% NaOH so I left It in the volumetric 1000ml flask for Ĺ hr while boiling some more water, cooling it in bottle w CO2 absorber. Then adding it too the volumetric flask before adding it back to the bottle + CO2 absorber.

Go back and read some of my previous answers. We soon learn to ALWAYS make more than enough. This is a common mistake and that's why you are taking the course. We learn by making mistakes. It can get discouraging but that's how we learn. Some lessons are painful BUT we usually don't repeat the mistakes.

Then comes titration problems todayÖI ATTEMPT to use the bottle to get NaOH solution by squeezing the bottle and end up getting NaOH solution going into the CO2 absorber as well as into the buretÖnot good at allÖin the end finally I get it to go only into the buret after pouring it into the buret with the funnel first, but everytime I finish squeezing some NaOH solution into the buret air goes back up that glass rod and into the storage bottle which if Iím not wrong, would expose the solution to all the CO2 in the air or is that supposed to happen?

It isn't supposed to happen and it won't happen IF the bottle fitted with the absorber has been constructed properly. There is a diagram in your text (in my edition its in the section on standardization of bases and the effect of CO2 on the standardization) which shows the proper construction. First the absorber tube. It has the absorbing material on the outside and the other end sticks into the inside of the bottle through a two-holed stopper; however, note that the tubing inside the bottle DOES NOT TOUCH THE LIQUID. Not even when the bottle is squeezed. If it does, the length of the inside part of the glass tube must be shortened. That is why NaOH is being squeezed into that part of the apparatus; i.e., the tube is too long. Next, for the other tube. That tube goes from the bottom of the absorber bottle at the very bottom of the liquid, through the stopper, and to the outside. Notice there is a pinch clamp on it. The pinch clamp is open to allow liquid to pass through, then closed to prevent air from entering.

Anyways with the standardizing of the HCl I put the solution of the HCl+ Na2CO3 + M.O indicator on a hot plate to boil after titrating it and was sitting there for about 10 min (time a wasting) so I asked the tech if I could place it into a cold water bath, tech says fine, I do that but it turned orange again.

Of course it turned orange again. The CO2 saturated solution (formed because you are titrating carbonate with HCl) is driven out of the solution by boiling, the pH rises back to the basic side of the solution (unless you have overtitrated it), you WANT it to turn back to the base color, then you are prepared to titrate further and you get the sharp end point of M.O. by adding a few more drops (dropwise at this stage of the titration).

I wasnít sure if that was supposed to happen so I ask tech and get a shoulder shrug =(Ö.is this what techs are for!? Is that supposed to happen?
I ask about color and get another ďumĒ and was also told that I could calculate about how much HCl I should add from the eqzn [Na2CO3+2HCl=>H2CO3 + 2NaCl] but Iím not exactly sure how to do that.

Stoichiometry 101

That was the reason I asked about the cold water bath since I'm kinda behind a few labs and the next one is Determination of Magnesium by complex formation titration in which I have to dissolve EDTA in water and wait for it too cool to room temp and since I'm behind I was thinking of a faster way to cool solutions which have just been heated but I'm not sure If for example I would have ppt come out of solution or some other unfunny rxn happen but I REALLY have got to speed up my pace in lab and all these waiting for solutions to cool to room temp on their own aren't helping...

Cooling as you have suggested above is fine.

For the 2nd part of the Determination of Mg by complex-titration, Determination of MgO by using EDTA as a titrant I have to use Eriochrome black indicator as a indicator, I was reading that the endpoint is when it turns blue but also that it also becomes pink after becoming blue.
When purifying the EDTA the crystal are supposed to be washed in a certain order with 1. Ethyl alcohol
2. acetone
3. ether
But why is that? And how many times with how much of each do you wash them with because it isnít mentioned.

My text gives a reference (1954) about preparing Na2H2Y.2H2O. But I don't know exactly what you are weighing. As your tech how to purify the EDTA.


And I might as well ask about the lab after that while Iím at itÖ In my lab 7 (Determination of hardness of water) it was changed from CaCO3 to (CH3COO)2CaH2O
instead, would that change anything about the lab besides the molar mass in the calculation?

That's all that will change.

In this lab I have to boil HCl to eliminate CO2 and I have the same Q I had last time on whatís the point if I have to let it cool to room temp (and if I can cool it with a cold water bath) and it will absorb CO2 again? After that I have to use Methyl red indicator and itís a Q of the color againÖThen I use 2ml buffer (ph10) and then titrate with a standard solution of EDTA + eriochrome black T. (what is eriochrome black T? I know from the lab before this one that itís an indicator but whatís with the T?)

I don't know what's with the T.





Go back and read some of my previous answers. We soon learn to ALWAYS make more than enough. This is a common mistake and that's why you are taking the course. We learn by making mistakes. It can get discouraging but that's how we learn. Some lessons are painful BUT we usually don't repeat the mistakes.

I know what you said, BUT I couldnít make more b/c I didnít have the liter capacity in my plastic bottle..I already did this lab last week and finished with the wine titration this week I found out I had just enough and had about 50 ml left by the looks of what was in the plastic bottle

It isn't supposed to happen and it won't happen IF the bottle fitted with the absorber has been constructed properly. There is a diagram in your text (in my edition its in the section on standardization of bases and the effect of CO2 on the standardization) which shows the proper construction. First the absorber tube. It has the absorbing material on the outside and the other end sticks into the inside of the bottle through a two-holed stopper; however, note that the tubing inside the bottle DOES NOT TOUCH THE LIQUID. Not even when the bottle is squeezed. If it does, the length of the inside part of the glass tube must be shortened. That is why NaOH is being squeezed into that part of the apparatus; i.e., the tube is too long. Next, for the other tube. That tube goes from the bottom of the absorber bottle at the very bottom of the liquid, through the stopper, and to the outside. Notice there is a pinch clamp on it. The pinch clamp is open to allow liquid to pass through, then closed to prevent air from entering.

Mine WAS constructed properly and I had 2 pictures to look at , 1 from the lab paper, 1 from the cd which replaced the standardization pgs in your bkÖ.the tube did NOT touch the solution at all, the tubing was so short that it was in line with the rubber stopper so my problem was actually not the tubing but with the liquid & the fact that the bottle was so tough to squeeze. I was squeezing the bottle till I was blue in the face (basically nobody else had a problem except me -_-::) and it was literally impossible to go and get the liquid to stay in the tube and clamp it at the same time b/c when I let go of the bottle it was misshapen so I had to press it back into itís original shape to be able to get solution out after that thus letting in air.

The results of my standardization however came out just like you said they would and I got 0.05446M for the NaOH concentration but it might have changed since I got air into the bottle.

Of course it turned orange again. The CO2 saturated solution (formed because you are titrating carbonate with HCl) is driven out of the solution by boiling, the pH rises back to the basic side of the solution (unless you have overtitrated it), you WANT it to turn back to the base color, then you are prepared to titrate further and you get the sharp end point of M.O. by adding a few more drops (dropwise at this stage of the titration).

Isnít the base color yellow? It turned +HCl salmon=> + heating=> orange => yellow => orange
I really donít know b/c this is what I did
1) Na2CO3 (0.2601g) HCl a) 53.59ml b) none after heating
2) Na2CO3 (0.2486g) HCl a) 50.15ml b) 0.79ml after heating
3) Na2CO3 ( 0.2257g) HCl a) 45.19ml b) 0.5ml after heating

Blank amount using NaCl ( 0.60ml) [I subtracted from total HCl amount added from each)

I did the math and got
0.09297M, 0.09320M, 0.09353M for the HCl concentration, does it look alright?
I forgot to mention that I added 8ml concentrated HCl to 992ml of distilled water to make the HCl solution in the first place.

Stoichiometry 101

Na2CO3+2HCl=>H2CO3 + 2NaCl
Fine..iíll just show you what I did and where I got stuck and maybe you can tell me what Iím missing or doing wrong
For the 1st one Have: 0.2601gNa2CO3, Mwt HCl (36.461g/mol), Mwt Na2CO3 (105.989g/mol)
Need ml of HCl
0.2601g Na2CO3 x 1molNa2CO3/105.989g = 0.002454mol Na2CO3
0.002454mol Na2CO3 x 2mol HCl/ 1mol Na2CO3 x 36.461g/mol = 0.17895g HCl

And hereís where Iím stuckÖhow do you find the ml needed approximately to titrate the Na2CO3 with if you just have this info? I donít have the Molarity of the HCl since Iím supposed to find that. Do you use the specific gravity of HCl (1.2g/ml) ?

My text gives a reference (1954) about preparing Na2H2Y.2H2O. But I don't know exactly what you are weighing. As your tech how to purify the EDTA.

I weighed out dried EDTA. The reference in the txt is referring to another bk which I donít have. What I posted before were the instructions of how to purify the EDTA and I was just curious as to just how much acetone, ether, and alchohol I was supposed to wash it with but since I didnít get a response from you I just poured it on until I felt like stopping (basically 2 filter volumes worth and hopefully that wasn't too much or too little)


I had to prepare KMnO4 solution by getting 3.2g KMnO4 and diluting it in 1300ml of water. MY instructions in the manual say to ďboilĒ it for 1hr 30min. It was well heating and then boiling at a slow slow bubble and as a result about 100ml evaporated and I was left with 1200ml. I was told that even if it said 1000ml had I boiled it/heated it down that much would not be able to fill a 1000ml vol flask because I have to put the solution in that after I go and filter out the MnO2
I read the text and it said heating for a ďbrief periodĒ was fine while the lab part in the text said to heat for 1hr, but Iím not sure if the purpose of them asking us to heat for 1hr 30min was to get it to reduce to 1L. Well if I heated it and left it there (text says to leave for 24hr) and let it sit there for a week before I filter would that be fine? The text does state that decomposition is slow as long as itís not exposed to light or heat etc. I left my solution in a beaker and covered it with aluminum foil. Iím not sure if I should stir it or do anything to it before filtering it. I also still have to finish titrating with the EDTA which is taking up the space in my 1000ml vol flask which I need to use to store the KMnO4 in but I was thinking of transferring the liquid after titrating my MgSO4 and unknown with the solution into a 500ml vol flask, but Iím just guessing that 500ml would be enough to titrate the hard water sample with.

thanks Dr.Bob








I looked back and saw that the post was extremely hard to read so i tried to fix it and hopefully it works, if not it'll just take up a bunch of room

Go back and read some of my previous answers. We soon learn to ALWAYS make more than enough. This is a common mistake and that's why you are taking the course. We learn by making mistakes. It can get discouraging but that's how we learn. Some lessons are painful BUT we usually don't repeat the mistakes. ď

I know what you said, BUT I couldnít make more b/c I didnít have the liter capacity in my plastic
bottle..I already did this lab last week and finished with the wine titration this week I found out I
had just enough and had about 50 ml left by the looks of what was in the plastic bottle

ĒIt isn't supposed to happen and it won't happen IF the bottle fitted with the absorber has been constructed properly. There is a diagram in your text (in my edition its in the section on standardization of bases and the effect of CO2 on the standardization) which shows the proper construction. First the absorber tube. It has the absorbing material on the outside and the other end sticks into the inside of the bottle through a two-holed stopper; however, note that the tubing inside the bottle DOES NOT TOUCH THE LIQUID. Not even when the bottle is squeezed. If it does, the length of the inside part of the glass tube must be shortened. That is why NaOH is being squeezed into that part of the apparatus; i.e., the tube is too long. Next, for the other tube. That tube goes from the bottom of the absorber bottle at the very bottom of the liquid, through the stopper, and to the outside. Notice there is a pinch clamp on it. The pinch clamp is open to allow liquid to pass through, then closed to prevent air from entering.


Mine WAS constructed properly and I had 2 pictures to look at , 1 from the lab paper, 1 from the cd which replaced the standardization pgs in your bkÖ.the tube did NOT touch the solution at all, the tubing was so short that it was in line with the rubber stopper so my problem was actually not the tubing but with the liquid & the fact that the bottle was so tough to squeeze. I was squeezing the bottle till I was blue in the face (basically nobody else had a problem except me -_-::) and it was literally impossible to go and get the liquid to stay in the tube and clamp it at the same time b/c when I let go of the bottle it was misshapen so I had to press it back into itís original shape to be able to get solution out after that thus letting in air.

The results of my standardization however came out just like you said they would and I got 0.05446M for the NaOH concentration but it might have changed since I got air into the bottle.


ĒOf course it turned orange again. The CO2 saturated solution (formed because you are titrating carbonate with HCl) is driven out of the solution by boiling, the pH rises back to the basic side of the solution (unless you have overtitrated it), you WANT it to turn back to the base color, then you are prepared to titrate further and you get the sharp end point of M.O. by adding a few more drops (dropwise at this stage of the titration).Ē


Isnít the base color yellow? It turned +HCl salmon=> + heating=> orange => yellow => orange
I really donít know b/c this is what I did
1) Na2CO3 (0.2601g) HCl a) 53.59ml b) none after heating
2) Na2CO3 (0.2486g) HCl a) 50.15ml b) 0.79ml after heating
3) Na2CO3 ( 0.2257g) HCl a) 45.19ml b) 0.5ml after heating

Blank amount using NaCl ( 0.60ml) [I subtracted from total HCl amount added from each)

I did the math and got
0.09297M, 0.09320M, 0.09353M for the HCl concentration, does it look alright?
I forgot to mention that I added 8ml concentrated HCl to 992ml of distilled water to make the HCl solution in the first place.

Stoichiometry 101


Na2CO3+2HCl=>H2CO3 + 2NaCl
Fine..iíll just show you what I did and where I got stuck and maybe you can tell me what Iím missing or doing wrong
For the 1st one Have: 0.2601gNa2CO3, Mwt HCl (36.461g/mol), Mwt Na2CO3 (105.989g/mol)
Need ml of HCl
0.2601g Na2CO3 x 1molNa2CO3/105.989g = 0.002454mol Na2CO3
0.002454mol Na2CO3 x 2mol HCl/ 1mol Na2CO3 x 36.461g/mol = 0.17895g HCl

And hereís where Iím stuckÖhow do you find the ml needed approximately to titrate the Na2CO3 with if you just have this info? I donít have the Molarity of the HCl since Iím supposed to find that. Do you use the specific gravity of HCl (1.2g/ml) ?

ĒMy text gives a reference (1954) about preparing Na2H2Y.2H2O. But I don't know exactly what you are weighing. As your tech how to purify the EDTA.Ē

I weighed out dried EDTA. The reference in the txt is referring to another bk which I donít have. What I posted before were the instructions of how to purify the EDTA and I was just curious as to just how much acetone, ether, and alchohol I was supposed to wash it with but since I didnít get a response from you I just poured it on until I felt like stopping (basically 2 filter volumes worth and hopefully that wasn't too much or too little)


I had to prepare KMnO4 solution by getting 3.2g KMnO4 and diluting it in 1300ml of water. MY instructions in the manual say to ďboilĒ it for 1hr 30min. It was well heating and then boiling at a slow slow bubble and as a result about 100ml evaporated and I was left with 1200ml. I was told that even if it said 1000ml had I boiled it/heated it down that much would not be able to fill a 1000ml vol flask because I have to put the solution in that after I go and filter out the MnO2
I read the text and it said heating for a ďbrief periodĒ was fine while the lab part in the text said to heat for 1hr, but Iím not sure if the purpose of them asking us to heat for 1hr 30min was to get it to reduce to 1L. Well if I heated it and left it there (text says to leave for 24hr) and let it sit there for a week before I filter would that be fine? The text does state that decomposition is slow as long as itís not exposed to light or heat etc. I left my solution in a beaker and covered it with aluminum foil. Iím not sure if I should stir it or do anything to it before filtering it. I also still have to finish titrating with the EDTA which is taking up the space in my 1000ml vol flask which I need to use to store the KMnO4 in but I was thinking of transferring the liquid after titrating my MgSO4 and unknown with the solution into a 500ml vol flask, but Iím just guessing that 500ml would be enough to titrate the hard water sample with.

thanks Dr.Bob


All things consiered, I think things turned out quite well for you.

Go back and read some of my previous answers. We soon learn to ALWAYS make more than enough. This is a common mistake and that's why you are taking the course. We learn by making mistakes. It can get discouraging but that's how we learn. Some lessons are painful BUT we usually don't repeat the mistakes.

I know what you said, BUT I couldnít make more b/c I didnít have the liter capacity in my plastic bottle..I already did this lab last week and finished with the wine titration this week I found out I had just enough and had about 50 ml left by the looks of what was in the plastic bottle

All's well that ends well.

It isn't supposed to happen and it won't happen IF the bottle fitted with the absorber has been constructed properly. There is a diagram in your text (in my edition its in the section on standardization of bases and the effect of CO2 on the standardization) which shows the proper construction. First the absorber tube. It has the absorbing material on the outside and the other end sticks into the inside of the bottle through a two-holed stopper; however, note that the tubing inside the bottle DOES NOT TOUCH THE LIQUID. Not even when the bottle is squeezed. If it does, the length of the inside part of the glass tube must be shortened. That is why NaOH is being squeezed into that part of the apparatus; i.e., the tube is too long. Next, for the other tube. That tube goes from the bottom of the absorber bottle at the very bottom of the liquid, through the stopper, and to the outside. Notice there is a pinch clamp on it. The pinch clamp is open to allow liquid to pass through, then closed to prevent air from entering.

Mine WAS constructed properly and I had 2 pictures to look at , 1 from the lab paper, 1 from the cd which replaced the standardization pgs in your bkÖ.the tube did NOT touch the solution at all, the tubing was so short that it was in line with the rubber stopper so my problem was actually not the tubing but with the liquid & the fact that the bottle was so tough to squeeze. I was squeezing the bottle till I was blue in the face (basically nobody else had a problem except me -_-::) and it was literally impossible to go and get the liquid to stay in the tube and clamp it at the same time b/c when I let go of the bottle it was misshapen so I had to press it back into itís original shape to be able to get solution out after that thus letting in air.

OK, it was constructed properly; however, something was not right else it would not have been necessary to squeeze the bottle so tight that it completely filled the bottle. I would think you could siphon it out and no squeezing would be necessary but that may be another subject.

The results of my standardization however came out just like you said they would and I got 0.05446M for the NaOH concentration but it might have changed since I got air into the bottle.

You're probably ok, especially since, in my opinion, and that of Skoog, West, and Holler, that M.O. titrates any Na2CO3 formed in the NaOH as a result of CO2 contamination, thus no error.

Of course it turned orange again. The CO2 saturated solution (formed because you are titrating carbonate with HCl) is driven out of the solution by boiling, the pH rises back to the basic side of the solution (unless you have overtitrated it), you WANT it to turn back to the base color, then you are prepared to titrate further and you get the sharp end point of M.O. by adding a few more drops (dropwise at this stage of the titration).

Isnít the base color yellow? It turned +HCl salmon=> + heating=> orange => yellow => orange
I really donít know b/c this is what I did
1) Na2CO3 (0.2601g) HCl a) 53.59ml b) none after heating
2) Na2CO3 (0.2486g) HCl a) 50.15ml b) 0.79ml after heating
3) Na2CO3 ( 0.2257g) HCl a) 45.19ml b) 0.5ml after heating

Blank amount using NaCl ( 0.60ml) [I subtracted from total HCl amount added from each)

I did the math and got
0.09297M, 0.09320M, 0.09353M for the HCl concentration, does it look alright?
I forgot to mention that I added 8ml concentrated HCl to 992ml of distilled water to make the HCl solution in the first place.

The first one may have been overtitrated since it required no additional HCl after heating; however, I took the average of your three numbers and obtained 0.09323. FROM THE AVERAGE, the lowest number is only 2.82 parts per thousand (0.28%) away, and the highest is only 3.18 ppt. Pretty good in my book, especially when all the problems you contended with are considered. We don't know, of course, what the actual numbers is; however, precision like that makes one feel a little better that the numbers are ok.

Stoichiometry 101

Na2CO3+2HCl=>H2CO3 + 2NaCl
Fine..iíll just show you what I did and where I got stuck and maybe you can tell me what Iím missing or doing wrong
For the 1st one Have: 0.2601gNa2CO3, Mwt HCl (36.461g/mol), Mwt Na2CO3 (105.989g/mol)
Need ml of HCl
0.2601g Na2CO3 x 1molNa2CO3/105.989g = 0.002454mol Na2CO3
0.002454mol Na2CO3 x 2mol HCl/ 1mol Na2CO3 x 36.461g/mol = 0.17895g HCl

And hereís where Iím stuckÖhow do you find the ml needed approximately to titrate the Na2CO3 with if you just have this info? I donít have the Molarity of the HCl since Iím supposed to find that. Do you use the specific gravity of HCl (1.2g/ml) ?

Yes, use the specific gravity.
1.2 g/mL x 1000 mL = 1200 grams/L if HCl is 100%, but it isn't. Look on the bottle. If it is a regular conc. HCl I think that is about 36% HCl; therefore, 1200 x 0.36 = 432 g/L and
432 g/L x (36.5 g HCl/1 mol HCl) = 11.8 M. Note that these bottles list the approximiate specific gravity and the approximate percent HCl; therefore, the 11.8 is just an approximate molarity. Then M HCl x L HCl= mols HCl and go from there. The ONLY reason for going through this calculation and what you showed earlier is that it gives an approximation for the volume of HCl needed in the titration. In view of the fact that the molarity of the HCl is so approximate, I always found it just wasn't worth the trouble; thus, I simply titrated and let the indicator tell me what I wantd to know.


My text gives a reference (1954) about preparing Na2H2Y.2H2O. But I don't know exactly what you are weighing. As your tech how to purify the EDTA.

I weighed out dried EDTA. The reference in the txt is referring to another bk which I donít have. What I posted before were the instructions of how to purify the EDTA and I was just curious as to just how much acetone, ether, and alchohol I was supposed to wash it with but since I didnít get a response from you I just poured it on until I felt like stopping (basically 2 filter volumes worth and hopefully that wasn't too much or too little).

That's what I would have done, too. When in doubt, use common sense.


I had to prepare KMnO4 solution by getting 3.2g KMnO4 and diluting it in 1300ml of water.

Do you know what the concentration of the KMnO4 is supposed to be? 3.2 g KMnO4/L is about 0.02 M. Extra volume just dilutes that. You can estimate the final volume and make a decision if the solution will be too weak to use.

MY instructions in the manual say to ďboilĒ it for 1hr 30min. It was well heating and then boiling at a slow slow bubble and as a result about 100ml evaporated and I was left with 1200ml. I was told that even if it said 1000ml had I boiled it/heated it down that much would not be able to fill a 1000ml vol flask because I have to put the solution in that after I go and filter out the MnO2
I read the text and it said heating for a ďbrief periodĒ was fine while the lab part in the text said to heat for 1hr, but Iím not sure if the purpose of them asking us to heat for 1hr 30min was to get it to reduce to 1L.

I suspect the extra boiling time was meant to reduce the volume. With due regard and respect for your lab instructions, I would have saved time by calculating the mass KMnO4 needed for about 1200 mL (knowing the concentration I needed), heated for about half an hour, let stand at least overnight, filtered, dumped the excess, and been ready to go.

Well if I heated it and left it there (text says to leave for 24hr) and let it sit there for a week before I filter would that be fine?

sure.

The text does state that decomposition is slow as long as itís not exposed to light or heat etc. I left my solution in a beaker and covered it with aluminum foil. Iím not sure if I should stir it or do anything to it before filtering it.

I advise against stirring it. As well, I would decant as I poured it into the filter funnel and I would leave the last 100 mL or so in the beaker. My philosophy is the more MnO2 we leave in the beaker the less we have to worry about the efficiency of the filter funnel.

Anything from 24 hr to longer is fine as long as we aren't talking about 2-3 months. The decomposition IS slow, and it really doesn't matter to you how much decomposes as long as the final concentration of the KMnO4 is within prescribed limits. The most important time constraint is that you filter, standardize, and titrate the unknown in the minimum time necessary. That means I would have everything set to go, then filter, then standardize, then do the unknown. My experience is that GOOD KMnO4 (filtered of all MnO2 since that catalyzes the decomposition) is good for at least a week. My instructors always told me that they wouldn't trust standardization results after a week which is why I had everything ready to go when I filtered. That way I never kept my standardized KMnO4 solution more than a few days (a week at the most). But all of that pertains to efficiency and being orderly and managing your time well. As a beginner, however, you know this is a LEARNING experience, too.

I also still have to finish titrating with the EDTA which is taking up the space in my 1000ml vol flask which I need to use to store the KMnO4 in but I was thinking of transferring the liquid after titrating my MgSO4 and unknown with the solution into a 500ml vol flask, but Iím just guessing that 500ml would be enough to titrate the hard water sample with.

I would guess, also, that 500 mL would be plenty if you have just the one titration to do (three times, I guess). But standardization will take more than that and if you have trouble extra needs to be added for that.


In the first place, how do you type something in bold type?

"OK, it was constructed properly; however, something was not right else it would not have been necessary to squeeze the bottle so tight that it completely filled the bottle. I would think you could siphon it out and no squeezing would be necessary but that may be another subject."

By siphon, I hope your not talking
about pipetting it out. Since I was
having a tough time trying to get
the NaOH out of the bottle I was
advised to go and pour it out, but
stubborn me decided to go and get
the solution out the "proper way."

The results of my standardization however came out just like you said they would and I got 0.05446M for the NaOH concentration but it might have changed since I got air into the bottle.

"You're probably ok, especially since, in my opinion, and that of Skoog, West, and Holler, that M.O. titrates any Na2CO3 formed in the NaOH as a result of CO2 contamination, thus no error."

Actually what I was worried about
was not the standardization but
when I had to titrate after with
that "air exposed" solution in the
bottle. I also had to wait over
the weekend to go and titrate the
wine and I'm more worried about
that since I used that solution.
But since I did titrate the
KHP unknown and also the vinegar
in the same day I think the
results should have come out
fine.I don't know about the
unknown but I got 61.90%,
57.61%,62.44% and I did the Q test
for the 57% but since it passed
that I averaged it and got 60.65%.
The results could be off but I
hope I made the right decision to
average it out. From what I read
in the text the vinegar shouldn't
have been more than 5% acid and my
average was 5.238% so I think that
turned out alright. Basically what
happened with the wine on mon was
that I was once again "color
challenged", I didn't know what
type of brown was brown...forget
it what I do know is that
according to the text the %
tartaric acid is supposed to be
less than 1% and I'll go see what
I get for that.

"Yes, use the specific gravity.
1.2 g/mL x 1000 mL = 1200 grams/L if HCl is 100%, but it isn't. Look on the bottle. If it is a regular conc. HCl I think that is about 36% HCl; therefore, 1200 x 0.36 = 432 g/L and
432 g/L x (36.5 g HCl/1 mol HCl) = 11.8 M. Note that these bottles list the approximiate specific gravity and the approximate percent HCl; therefore, the 11.8 is just an approximate molarity. Then M HCl x L HCl= mols HCl and go from there. The ONLY reason for going through this calculation and what you showed earlier is that it gives an approximation for the volume of HCl needed in the titration. In view of the fact that the molarity of the HCl is so approximate, I always found it just wasn't worth the trouble; thus, I simply titrated and let the indicator tell me what I wantd to know."

I really wouldn't get anything off
the bottle since the bottle they
had the concent HCl in wasn't the
original bottle. The label on the
container consisted of a
handwritten "concentrated HCl".
For other titrations would it be
practical to go and estimate the
ammount needed to titrate or would
it be a waste of time like aprox
the HCl ml needed?

I had to prepare KMnO4 solution by getting 3.2g KMnO4 and diluting it in 1300ml of water.

"Do you know what the concentration of the KMnO4 is supposed to be? 3.2 g KMnO4/L is about 0.02 M. Extra volume just dilutes that. You can estimate the final volume and make a decision if the solution will be too weak to use."

No, I don't know isn't that the
whole reason for standardization?
If I don't know what the M is
supposed to be will it still
matter what the concentration is?
I would just be using more or less
right?

"I suspect the extra boiling time was meant to reduce the volume. With due regard and respect for your lab instructions, I would have saved time by calculating the mass KMnO4 needed for about 1200 mL (knowing the concentration I needed), heated for about half an hour, let stand at least overnight, filtered, dumped the excess, and been ready to go."

Not knowing the supposed
concentration leaves me in a bit
of an awkward situation I guess.

"I advise against stirring it. As well, I would decant as I poured it into the filter funnel and I would leave the last 100 mL or so in the beaker. My philosophy is the more MnO2 we leave in the beaker the less we have to worry about the efficiency of the filter funnel."

About the efficiency of the filter
funnel, I had to go and clean a fritted funnel with a mix of 100ml 1M H2SO4 and 10ml peroxide. Is it just to clean the filter? B/c when I did the lab on the gravimetric determination of chloride I cleaned the fritted funnels with 5ml concentrated HNO3 and 5ml 6M NH3. I cleaned it and left it in the dessicator, I think that would be fine.

"Anything from 24 hr to longer is fine as long as we aren't talking about 2-3 months. The decomposition IS slow, and it really doesn't matter to you how much decomposes as long as the final concentration of the KMnO4 is within prescribed limits. The most important time constraint is that you filter, standardize, and titrate the unknown in the minimum time necessary. That means I would have everything set to go, then filter, then standardize, then do the unknown. My experience is that GOOD KMnO4 (filtered of all MnO2 since that catalyzes the decomposition) is good for at least a week. My instructors always told me that they wouldn't trust standardization results after a week which is why I had everything ready to go when I filtered. That way I never kept my standardized KMnO4 solution more than a few days (a week at the most). But all of that pertains to efficiency and being orderly and managing your time well. As a beginner, however, you know this is a LEARNING experience, too."

Again, it would be nice to have a prescribed limit but I don't have one. I have to use the KMnO4 for 2 more other labs after the filtering and standardizing (Determining the % of iron in an iron ore sample [unknown]
& Determining the % of iron in a razor blade) But since I didn't do the EDTA titration yet ( for MgSO4, unknown, and hard water) I'm gonna have to do that on Mon which would if I'm lucky leave some time to go and filter but I dont think I'm gonna be able to. So basically that would leave that for Wed hypothetically and from that day with standardizations to the next mon would be 6 days. Hmm...
But when you say that's a learning experience, I've heard that you only do titrations in analytical chem and not much after that if I'm not wrong.

"I would guess, also, that 500 mL would be plenty if you have just the one titration to do (three times, I guess). But standardization will take more than that and if you have trouble extra needs to be added for that."

Yep, 3 trials. But I'm not instructed to go and standardize the EDTA, just to and calculate the molarity after I add 3.800g to 1L of water in a vol flask (given M= g dry sample/ Mwt EDTA)











In the first place, how do you type something in bold type?

To bold, type < followed by b followed by >. To unbold, type < followed by / followed by b followed by >.

"OK, it was constructed properly; however, something was not right else it would not have been necessary to squeeze the bottle so tight that it completely filled the bottle. I would think you could siphon it out and no squeezing would be necessary but that may be another subject."

By siphon, I hope your not talking
about pipetting it out. Since I was
having a tough time trying to get
the NaOH out of the bottle I was
advised to go and pour it out, but
stubborn me decided to go and get
the solution out the "proper way."

No, I'm not talking about using a pipet. Personally, I think pouring it out is fine.

The results of my standardization however came out just like you said they would and I got 0.05446M for the NaOH concentration but it might have changed since I got air into the bottle.

"You're probably ok, especially since, in my opinion, and that of Skoog, West, and Holler, that M.O. titrates any Na2CO3 formed in the NaOH as a result of CO2 contamination, thus no error."

Actually what I was worried about
was not the standardization but
when I had to titrate after with
that "air exposed" solution in the
bottle. I also had to wait over
the weekend to go and titrate the
wine and I'm more worried about
that since I used that solution.
But since I did titrate the
KHP unknown and also the vinegar
in the same day I think the
results should have come out
fine.I don't know about the
unknown but I got 61.90%,
57.61%,62.44% and I did the Q test
for the 57% but since it passed
that I averaged it and got 60.65%.
The results could be off but I
hope I made the right decision to
average it out. From what I read
in the text the vinegar shouldn't
have been more than 5% acid and my
average was 5.238% so I think that
turned out alright. Basically what
happened with the wine on mon was
that I was once again "color
challenged", I didn't know what
type of brown was brown...forget
it what I do know is that
according to the text the %
tartaric acid is supposed to be
less than 1% and I'll go see what
I get for that.

One never knows about the averaging thing but the Q test is a good one to use. And I think you did the right thing. Personally, I like to see a little better precision than that but with your numbers the suspected outlier should remain.


"Yes, use the specific gravity.
1.2 g/mL x 1000 mL = 1200 grams/L if HCl is 100%, but it isn't. Look on the bottle. If it is a regular conc. HCl I think that is about 36% HCl; therefore, 1200 x 0.36 = 432 g/L and
432 g/L x (36.5 g HCl/1 mol HCl) = 11.8 M. Note that these bottles list the approximiate specific gravity and the approximate percent HCl; therefore, the 11.8 is just an approximate molarity. Then M HCl x L HCl= mols HCl and go from there. The ONLY reason for going through this calculation and what you showed earlier is that it gives an approximation for the volume of HCl needed in the titration. In view of the fact that the molarity of the HCl is so approximate, I always found it just wasn't worth the trouble; thus, I simply titrated and let the indicator tell me what I wantd to know."

I really wouldn't get anything off
the bottle since the bottle they
had the concent HCl in wasn't the
original bottle. The label on the
container consisted of a
handwritten "concentrated HCl".
For other titrations would it be
practical to go and estimate the
ammount needed to titrate or would
it be a waste of time like aprox
the HCl ml needed?

Concentrated HCl is about 11.6 M. It is about 36-38% HCl. To use it to estimate the amount needed for a titration (or not to use it) is a personal thing. The calculation doesn't take that much time BUT since it is approximate, it gets you to within a few milliliters of the end point and I can tell when I'm within a mL or so just with the indicator.

I had to prepare KMnO4 solution by getting 3.2g KMnO4 and diluting it in 1300ml of water.

"Do you know what the concentration of the KMnO4 is supposed to be? 3.2 g KMnO4/L is about 0.02 M. Extra volume just dilutes that. You can estimate the final volume and make a decision if the solution will be too weak to use."

No, I don't know isn't that the
whole reason for standardization?
If I don't know what the M is
supposed to be will it still
matter what the concentration is?
I would just be using more or less
right?

Sometimes the lab procedures tell the approximate molarity we are to use; for example, in the preparation of NaOH the text said, "to prepare approximately 0.05 M NaOH, etc etc...". I thought perhaps the lab sheet you are using would give an approximate molarity. IF the idea of boiling for 1 hr and 30 min was to evaporate 300 mL water so the final volume was close to 1 L, then I would have used 3.2 g KMnO4, used about 1025 mL water, heated about 1/2 hour, filtered, and gone from there. The SAFE thing to do is to follow your lab procedure.

"I suspect the extra boiling time was meant to reduce the volume. With due regard and respect for your lab instructions, I would have saved time by calculating the mass KMnO4 needed for about 1200 mL (knowing the concentration I needed), heated for about half an hour, let stand at least overnight, filtered, dumped the excess, and been ready to go."

Not knowing the supposed
concentration leaves me in a bit
of an awkward situation I guess.

Not really. Just use the 3.2 g KMnO4 and follow the instructions.

"I advise against stirring it. As well, I would decant as I poured it into the filter funnel and I would leave the last 100 mL or so in the beaker. My philosophy is the more MnO2 we leave in the beaker the less we have to worry about the efficiency of the filter funnel."

About the efficiency of the filter
funnel, I had to go and clean a fritted funnel with a mix of 100ml 1M H2SO4 and 10ml peroxide. Is it just to clean the filter? B/c when I did the lab on the gravimetric determination of chloride I cleaned the fritted funnels with 5ml concentrated HNO3 and 5ml 6M NH3. I cleaned it and left it in the dessicator, I think that would be fine.

No, cleaning with HNO3 and NH3 worked well for the chloride because NH3 dissolves any AgCl that is retained in or on the fritted disk. For filtering KMnO4, you want to use the H2O2 to oxidize anything there so the KMnO4 will not oxidize it when it is filtered. If any oxidizible material is on the fritted disk, KMnO4 will oxidize it, the KMnO4 will be reduced to Mn+2 ion (but more probably to MnO2) and any MnO2 in the solution catalyzes (I don't think I spelled that right) the decomposition reaction. One purpose of the H2SO4 is to make sure the solution is acid for the H2O2 step.

"Anything from 24 hr to longer is fine as long as we aren't talking about 2-3 months. The decomposition IS slow, and it really doesn't matter to you how much decomposes as long as the final concentration of the KMnO4 is within prescribed limits. The most important time constraint is that you filter, standardize, and titrate the unknown in the minimum time necessary. That means I would have everything set to go, then filter, then standardize, then do the unknown. My experience is that GOOD KMnO4 (filtered of all MnO2 since that catalyzes the decomposition) is good for at least a week. My instructors always told me that they wouldn't trust standardization results after a week which is why I had everything ready to go when I filtered. That way I never kept my standardized KMnO4 solution more than a few days (a week at the most). But all of that pertains to efficiency and being orderly and managing your time well. As a beginner, however, you know this is a LEARNING experience, too."

Again, it would be nice to have a prescribed limit but I don't have one. I have to use the KMnO4 for 2 more other labs after the filtering and standardizing (Determining the % of iron in an iron ore sample [unknown]
& Determining the % of iron in a razor blade) But since I didn't do the EDTA titration yet ( for MgSO4, unknown, and hard water) I'm gonna have to do that on Mon which would if I'm lucky leave some time to go and filter but I dont think I'm gonna be able to. So basically that would leave that for Wed hypothetically and from that day with standardizations to the next mon would be 6 days. Hmm...

I wouldn't worry about it. Six days is probably ok if kept in the dark.

But when you say that's a learning experience, I've heard that you only do titrations in analytical chem and not much after that if I'm not wrong.

You're talking to the wrong guy here. I'm an analytical chemist and I have spent my life titrating, teaching titrating, doing gravimetry and teaching gravimetry, etc etc. I think quant is the most interesting course in college. And about the time we think there isn't anything left to determine analytically, someone comes along and offers a course in ORGANIC quant. That's another VERY interesting course. When we tire of that we get into microchemistry where 1 nanogram is a BUNCH of material. But, I see I'm on my soapbox. :-)

"I would guess, also, that 500 mL would be plenty if you have just the one titration to do (three times, I guess). But standardization will take more than that and if you have trouble extra needs to be added for that."

Yep, 3 trials. But I'm not instructed to go and standardize the EDTA, just to and calculate the molarity after I add 3.800g to 1L of water in a vol flask (given M= g dry sample/ Mwt EDTA)

OK, you're using EDTA as a primary standard which is why you want to have a clean, dry, pure, sample. By the way, I would see if I couldn't borrow, beg, buy, whatever, another flask. When I was a student we had a stockroom and we could check out what we needed. Of course we had to return it when the class was over (or pay for it if lost, broken, too dirty to clean, etc) but it certainly speeded up the process in the lab. I never had to finish one experiment in order to have equipment to do the next one. Perhaps the "New" chemistry is being taught differently. :-)


No, I'm not talking about using a pipet. Personally, I think pouring it out is fine.

what exactly were you talking about when you said "siphon"?

Sometimes the lab procedures tell the approximate molarity we are to use; for example, in the preparation of NaOH the text said, "to prepare approximately 0.05 M NaOH, etc etc...". I thought perhaps the lab sheet you are using would give an approximate molarity. IF the idea of boiling for 1 hr and 30 min was to evaporate 300 mL water so the final volume was close to 1 L, then I would have used 3.2 g KMnO4, used about 1025 mL water, heated about 1/2 hour, filtered, and gone from there. The SAFE thing to do is to follow your lab procedure.

well I did follow the lab manual so..now I just have to filter. But I'll keep that in mind if I ever have to deal with KMnO4 again which I think I will but not in quant of course.

No, cleaning with HNO3 and NH3 worked well for the chloride because NH3 dissolves any AgCl that is retained in or on the fritted disk. For filtering KMnO4, you want to use the H2O2 to oxidize anything there so the KMnO4 will not oxidize it when it is filtered. If any oxidizible material is on the fritted disk, KMnO4 will oxidize it, the KMnO4 will be reduced to Mn+2 ion (but more probably to MnO2) and any MnO2 in the solution catalyzes (I don't think I spelled that right) the decomposition reaction. One purpose of the H2SO4 is to make sure the solution is acid for the H2O2 step.

uh oh I just read the lab manual for the prep of 0.02M KMnO4 and it said that during the washing of the fritted funnel after going and filtering the H2SO4 1M and 3%peroxide I'm supposed to rinse with "copious amounts of water" and I didn't...I just let it sit in the dessicator and thats where it still lies. Should I try and use some water to rinse it with? My lab manual convienently didn't mention this. I swear they just copy what's in the text. And catalyzes is spelled correctly

You're talking to the wrong guy here. I'm an analytical chemist and I have spent my life titrating, teaching titrating, doing gravimetry and teaching gravimetry, etc etc. I think quant is the most interesting course in college. And about the time we think there isn't anything left to determine analytically, someone comes along and offers a course in ORGANIC quant. That's another VERY interesting course. When we tire of that we get into microchemistry where 1 nanogram is a BUNCH of material. But, I see I'm on my soapbox. :-)

Well good for you, at least you found something that you like to do.My major is in forensics. I've never heard of Organic quant but I haven't taken organic yet. Hopefully won't be that bad...An interesting fact I heard from the replacement tech for a day was that a zeto mole (I just heard it so I could be spelling it completely wrong) is 10^-21 mole [he was reading chemical enginering] You may find that interesting or you may know that, he sure found it interesting..=).

OK, you're using EDTA as a primary standard which is why you want to have a clean, dry, pure, sample. By the way, I would see if I couldn't borrow, beg, buy, whatever, another flask. When I was a student we had a stockroom and we could check out what we needed. Of course we had to return it when the class was over (or pay for it if lost, broken, too dirty to clean, etc) but it certainly speeded up the process in the lab. I never had to finish one experiment in order to have equipment to do the next one. Perhaps the "New" chemistry is being taught differently. :-)


I was kind of afraid of asking for another one...I'll admit I since starting the course have broke a 2 2000ml beakers, a funnel, and a buret (which I had calibrated 2weeks prior), and knocked someone's fritted funnel into the sink and well, broke that too.
But I'll try...
In general chem I could just grab another graduated cylinder from another drawer and basically everyone just switched around but now all I have is a...I'm not kidding...storage bin and 1 assigned buret. (since I broke that original one I have this broken top one...they're so darn cheap, but lab is oh so expensive)

I really wish I had more than 1 of everything and just 3 250ml erlenmeyer flasks...

Well if this is "New" chemistry then I want the old..





No, I'm not talking about using a pipet. Personally, I think pouring it out is fine.

what exactly were you talking about when you said "siphon"?

It's easier for you to look siphon up in the dictionary or in a glossary than to try to write out an explanation. Or you might try Google; just type in siphon and read the results.

Sometimes the lab procedures tell the approximate molarity we are to use; for example, in the preparation of NaOH the text said, "to prepare approximately 0.05 M NaOH, etc etc...". I thought perhaps the lab sheet you are using would give an approximate molarity. IF the idea of boiling for 1 hr and 30 min was to evaporate 300 mL water so the final volume was close to 1 L, then I would have used 3.2 g KMnO4, used about 1025 mL water, heated about 1/2 hour, filtered, and gone from there. The SAFE thing to do is to follow your lab procedure.

well I did follow the lab manual so..now I just have to filter. But I'll keep that in mind if I ever have to deal with KMnO4 again which I think I will but not in quant of course.

No, cleaning with HNO3 and NH3 worked well for the chloride because NH3 dissolves any AgCl that is retained in or on the fritted disk. For filtering KMnO4, you want to use the H2O2 to oxidize anything there so the KMnO4 will not oxidize it when it is filtered. If any oxidizible material is on the fritted disk, KMnO4 will oxidize it, the KMnO4 will be reduced to Mn+2 ion (but more probably to MnO2) and any MnO2 in the solution catalyzes (I don't think I spelled that right) the decomposition reaction. One purpose of the H2SO4 is to make sure the solution is acid for the H2O2 step.

uh oh I just read the lab manual for the prep of 0.02M KMnO4 and it said that during the washing of the fritted funnel after going and filtering the H2SO4 1M and 3%peroxide I'm supposed to rinse with "copious amounts of water" and I didn't...I just let it sit in the dessicator and thats where it still lies. Should I try and use some water to rinse it with? My lab manual convienently didn't mention this. I swear they just copy what's in the text. And catalyzes is spelled correctly

Yes, hook up the frit (I suppose you use a suction flask) and rinse it with SEVERAL (meaning 5 or 6 50-mL portions of distilled/deionized water. You can do this just before filter the KMnO4 as the frit need not be dry.

You're talking to the wrong guy here. I'm an analytical chemist and I have spent my life titrating, teaching titrating, doing gravimetry and teaching gravimetry, etc etc. I think quant is the most interesting course in college. And about the time we think there isn't anything left to determine analytically, someone comes along and offers a course in ORGANIC quant. That's another VERY interesting course. When we tire of that we get into microchemistry where 1 nanogram is a BUNCH of material. But, I see I'm on my soapbox. :-)

Well good for you, at least you found something that you like to do.My major is in forensics. I've never heard of Organic quant but I haven't taken organic yet. Hopefully won't be that bad...An interesting fact I heard from the replacement tech for a day was that a zeto mole (I just heard it so I could be spelling it completely wrong) is 10^-21 mole [he was reading chemical enginering] You may find that interesting or you may know that, he sure found it interesting..=).

A zeptomole is 10^-21 mole. A yactomole is 10^-24 mole.
The prefixes, by 10^-3 are (starting at unit):
unit (100
milli
micro
nano
pico
femto
atto
zepto
yacto. 10-24

For prefixes going the other way, from 10o to 1024, and starting at unit, are:
unit
kilo
mega
giga
tera
peta
exa
zetta
yotta


OK, you're using EDTA as a primary standard which is why you want to have a clean, dry, pure, sample. By the way, I would see if I couldn't borrow, beg, buy, whatever, another flask. When I was a student we had a stockroom and we could check out what we needed. Of course we had to return it when the class was over (or pay for it if lost, broken, too dirty to clean, etc) but it certainly speeded up the process in the lab. I never had to finish one experiment in order to have equipment to do the next one. Perhaps the "New" chemistry is being taught differently. :-)


I was kind of afraid of asking for another one...I'll admit I since starting the course have broke a 2 2000ml beakers, a funnel, and a buret (which I had calibrated 2weeks prior), and knocked someone's fritted funnel into the sink and well, broke that too.
But I'll try...
In general chem I could just grab another graduated cylinder from another drawer and basically everyone just switched around but now all I have is a...I'm not kidding...storage bin and 1 assigned buret. (since I broke that original one I have this broken top one...they're so darn cheap, but lab is oh so expensive)

I really wish I had more than 1 of everything and just 3 250ml erlenmeyer flasks...

Well if this is "New" chemistry then I want the old..


Okay thanks for all the advice Dr.Bob

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