Thursday
March 5, 2015

Posts by DrBob222


Total # Posts: 47,454

Chemistry
I don't think so. 40 -(-20) = 60 and for an exothermic reaction you add Ea forward to |dH| so that is 40+20= 60 kJ/mol.
February 8, 2015

chemistry
1 mol of a gas at STP occupies 22.4L; therefore, 7.08 mols must occupy .....L.
February 7, 2015

chemistry
How much heat do you need? q = mass H2O x specific heat H2O x dT q = 150g x 4.18 J/g x 75 = approx 47000 J but you need to go through all of these calculations and redo them for better accuracy. You will lose 75% (or keep 25%) so we must increase that to approx 47,000/0.25 = ...
February 7, 2015

Chemistry
I answered this under the science post.
February 7, 2015

science
What's the M of the NaOH after mixing and before reaction? 0.200 M NaOH x (14.0/(14.0+42.4) = approx 0.00025. Since there is 1 Na^+ in 1 molecule of NaOH, 0.00025 is the M of the Na^+. The nitrate is done the same way. You need not worry about the reaction since Na^+ and ...
February 7, 2015

chemistry
Isn't this the same as your previous two or three dG problems?
February 7, 2015

chemistry
volume = mass/density
February 7, 2015

chemistry
Works the same way as dG but this is dH. Write ad balance the equation. dHrxn = (n*dHo products) - (n*dHo reactants). Of course you will need ton convert 25 lbs to grams.
February 7, 2015

chemistry
dGorxn = (n*dGo formation products) - (n*dGo formation reactants) gives you the dG for the reaction. Call that Y. Then dG for 4.70 g Ca will be Y kJ/mol x (# mols Ca in 4.70g) = ? You may want to write and balance the equation.
February 7, 2015

chemistry
I wonder if that is Cu(NO3)2. mols = grams/molar mass. Then M = mols/l. mols is ? from above. Solve for L. You know m = 0.180
February 7, 2015

To the impersonator
You are welcome to answer questions on this board but not under my name. Please use another screen name. You're use of Bob is acceptable but not DrBob222. I CAN ban you from the site if it becomes necessary.
February 7, 2015

Chemistry
You use the molar mass of the material for which you have a mass; i.e., if your material weighed is KH2PO4 then mols KH2PO4 = grams KH2PO4/molar mass kH2PO4.
February 7, 2015

Chemistry
The base is K2HPO4. The acid is KH2PO4. Convert g base to mols. mols = grams/molar mass. Do the same for the acid. Convert each to M. M = mols/L. Then substitute into the HH equation and solve for pH.
February 7, 2015

Chemistry
What's the question?
February 7, 2015

Physical Science
WHICH ONE HAS A HALF-LIFE OF 60.6?
February 7, 2015

Physical Science
So the Bi has gone through 1 half life since it has decreased from 200 g to 100 g. And it did that in 60.6 minutes so the half life of the isotope must be 60.6 minutes. and that is .......?
February 7, 2015

chemistry
Which do you think has more randomness? and why?
February 7, 2015

chemistry
Balance the equations. dGorxn = (n*dGoformation products) - (n*dGo formation reactants) The rxn is not spontaneous if dGo rxn at std conditions is +.
February 7, 2015

chemistry
Same question here. Which do you think move from more random to less random and why? For example, #4 is more random because there are more moles gas on the right than left. #5 is less random because the molecules in liquid water are more free to move around than in ice where ...
February 7, 2015

chemistry
dG = dH - TdS Set dG = 0 and solve for T in kelvin. Remember to make the units the same (they aren't now).
February 7, 2015

math
Ms. Sue gave you the numbers. All you had to do was to divide them. 576,650,390,625/38,443,359,375 = 15. Punch it in your calculator and see. The way I did it is a short cut. No matter how you slice it, however, the answer is 15.
February 7, 2015

math
A few typos but the answer is right at 15. 1510/159 = 1510-9 = 151 = 15
February 7, 2015

math
1510/159</ = 1510-9 = 151 = 15
February 7, 2015

Chemistry
A = ebc where e = molar absorptivity 0.600 = e*1.0*9.8E-6 e = ?
February 7, 2015

chemistry
NH3 + HNO3 ==> NH4NO3 + H2O millimols NH3 = 100 x 0.2 = 20 mmols HNO3 = 50 x 0.5 = 25 So you've added enough HNO3 to neutralize all of the NH3 and have an excess of 5 mmols HNO3 left. That's in 100 + 50 = 150 mL M HNO3 = mmols/ml = ?M
February 7, 2015

chemistry
The highest pKa value means the weakest acid. Why not look up the Ka or pKa values and see. http://clas.sa.ucsb.edu/staff/Resource%20Folder/Chem109ABC/Acid,%20Base%20Strength/Table%20of%20Acids%20w%20Kas%20and%20pKas.pdf
February 7, 2015

chemistry
pKb = 3.8. Kb = -log 3.8 Kb = approx 1.6E-4 but you should get a better answer than that. .......BNH2 + HOH --> BNH3^+ + OH^- I......0.01............0.......0 C......-x..............x.......x E......0.01-x..........x.......x Kb = 1.6E-4 = (x)(x)/(0.01-x) Solve for x = (OH...
February 7, 2015

chemistry
pk of 1 is stronger than pk of 2 is stronger than pk 9, etc. That should make it easy to arrange.
February 7, 2015

chemistry
The way you have displayed the answers I can't tell what is what. Here is the Ka equation for the NH4^+. NH4^+ + H2O ==> NH3 + H3O^+ Except for the missing charge on H3O^+, #4 appears the closest.
February 7, 2015

chemistry
#5 is a quite strong "weak" acid. The pKa value is about 0.7. All of the other acids listed are weaker.
February 7, 2015

Chemistry (Gen Chem 1)
140 pm/atom x #atoms = 6.70E10 pm
February 7, 2015

Chem/Hydrocarbons
I don't think there are any mathematical formulas that will tell you how many isomers a particular compound has, even for the simple straight chain compounds. There may be some hints on this page. http://www.ehow.com/how_6931563_calculate-number-isomers.html 1 or 2 or 3 ...
February 7, 2015

chemistry
You're guessing. Volume = l x w x h density = mass/volume. volume = 6.88 x 2.03 x 1.85 = ? cubic centimeters density = g mass/volume cc = ?
February 6, 2015

Chemistry
Did you look at my answer below? Don't post an exact duplicate without acknowledging that answer.
February 6, 2015

Chemistry
Thanks for letting me know.
February 6, 2015

Chemistry
I don't know what you did. My crystal ball is not working very well today.
February 6, 2015

chemistry
How many sides does this block have. Only two?
February 6, 2015

Chemistry
I made a typo so I erased the page and reposted this. I can't visualize it and my attempted drawings doin't help. I found this site on the web and appears to be what you are describing if you look at the pink one (I think three from the left) and the"clear" ...
February 6, 2015

Chemistry
Does 8 + 38 = 17 + 19 ?
February 6, 2015

Chemistry
Use the Henderson-Hasselbalch equation. pH = pKa + log (base)/(acid) Your two big problems. 1. What pKa do you use? 2. which is the acid and which the base. 3. (Actually, it doesn't matter which is the acid and which the base because the concentrations are equal which ...
February 6, 2015

Chemistry
2KClO3 ==> 2KCl + 3O2 Loss in mass = mass O2 lost = 1.042-0.943 = 0.099 mols O2 = grams/molar mass Using the coefficients in the balanced equation, convert mols O2 to mols KClO3. Then convert mols KClO3 to grams KClO3 with g = mols x molar mass.
February 6, 2015

chemistry
Yes there are. mols = grams/molar mass and 1 mol of anything(NaCl for example) contains 6.02E23 molecules of anythings (molecules NaCl for example) The two facts will work all of the question marks although some of the equations must be rearranged.
February 6, 2015

Chemistry AP
Thanks for the update. Someone should tell that Quest system that it is not doing the students a favor by implying that those additional digits are good ones. I guess those extra digits are being used to know if the answer is correct or not; the thinking must be that this way ...
February 5, 2015

Chemistry AP
I can assure you that the pH is 4.80 ad not that long string of numbers you have. You're allowed only 3 significant figures--all of the numbers after that don't count.
February 5, 2015

Chemistry AP
I forgot to mention that there is another way to do it if yu want to go to the trouble. You can not ignore the x and make a quadratic equation out of it, then solve the quadratic. However, you will get the same answer. 5.55E-10 = x^2/(0.44-x) 5.55E-10*(0.44-x) = x^2 5.55E-10*0...
February 5, 2015

Chemistry AP
5.55E-10 = (x)^2/0.44-x x is small in comparison to 0.44 so ignore it. Then x^2 = 5.55E-10*0.44 Then x^2 = 2.44E-10 Solve for x and convert to pH. I don't know about a 10^3 rule but I know the x is small and can be ignored. Continuing with my work, then x = sqrt(2.44E-10) ...
February 5, 2015

Chemistry AP
You're right that Ka = Kw/Kb = 5.55E-10 But your equation is wrong. Here is the hydrolysis equation which you need. .........NH4^+ + H2O ==> NH3 + H3O^+ I........0.44.............0......0 C.........-x..............x......x E.......0.44-x............x.......x Then Ka = (...
February 5, 2015

MATH--(REALLY NEED HELP )
We can't tell by reading "really need help" what kind of help you need. Be sure to put the SUBJECT in the subject line. You will get help faster that way.
February 5, 2015

chemistry
How much of this do you know how to do on your own. Explain exactly what you don't understand about it.
February 5, 2015

chemistry
M methanol = mols methanol/L solution. mols methanol = grams/molar mass = ? L solution = volume methanol + acetonitrile. Convert g methanol to mL methanol using density. Add to volume of acetonitile (mL + mL) and convert to L. Plug L into the mols/L above and solve for M ...
February 5, 2015

chemistry
C = k*P 0.25 = k*P. Solve for P
February 5, 2015

chemistry
See your post above. Same formula.
February 5, 2015

Chemistry
The one at higher T.
February 5, 2015

Science
Probably. If no air pressure, no air and if the "animal" breathes s/he is in trouble.
February 5, 2015

chemistry
............Bi2S3 --> 2Bi^2+ + 3S^2- Initial.....solid......0........0 Change......solid......2x.......3x equilibrium.solid......2x........3x Ksp = (Bi^3+)^2(S^2-)^3 Substitute the E line into the Ksp equation and solve for x. x will give you the solubility in mols/L. ...
February 5, 2015

CHEMISTRY
You would do well to post just one problem to the post. This one is done just the reverse of the Ag2SO4. .........Cr(OH)3 ==> Cr^3+ + 3OH^- Initial..solid........0.......0 change...solid........x.......3x equilibrium solid.....x........3x Ksp = (Cr^3+))(OH^-)^3 Substitute ...
February 5, 2015

CHEMISTRY
........Ag2SO4 ==> 2Ag^2+ + SO4^2- I.......solid.......0..........0 C.......solid.....2*3.85E-9..3.85E-9 E.......solid.....7.7E-9.....3.85E-9 Ksp = (Ag^+)^2(SO4^2-) Ksp = (7.7E-9)^2(3.85E-9) Ksp = ? You were right to calculate solubility in mols/L as you did and you have ...
February 5, 2015

Chemistry
M = mols/L. You want 0.073M HClO and you want 0.250 L so that is 0.073 = mols/0.250 so mols = approx 0.01825 (I am using more significant figures than allowd---a few guard digits). Basically you want 18.25 mmols HClO in the solution. For the base, you want mmols 250 x 0.046 = ...
February 5, 2015

Chemistry
The buffer capacity = mols acid/base needed to change the pH of a L of the buffer by 1 unit. molos added = 0.00419L x 0.24M = ? Then ?/25 mL x (1000/25) = mols to change 1L by 1 units = ? You can put this into equatio form with mL as mLacid x Macid/mL buffer = 4.19 x 0.24/25....
February 5, 2015

chemistry
Why can't you use the same screen names. It's confusing to us and we could help better if you kept the same screen name. Cole; Antonette; Luke; et al. It took awhile but here it is. For pH = 0.91,you have 0.91 = 1.26 + log (base)/(acid) B/A = approx 0.447 but you need ...
February 5, 2015

Chemistry
Probably none. I'm sure you meant FLUORINE and not fluoride. Just set up a proportion. (1.55/1.10) = (2.42/x) and solve for x
February 5, 2015

chemistry
The first thing you need to do is write and balance the equation. then I can help.
February 5, 2015

chemistry
dG = dH - TdS Remember to convert dS in J/K to kJ. Also remember T must be in kelvin.
February 5, 2015

Chemistry
What's the problem with #2? Just take equal amount of A and B (it doesn't mattr how many g you take as long as the amounts are equal). Calculate X of each and from there solve for p of each. I can help you if you get stuck.
February 4, 2015

Chemistry
pi = iMRT Solve for i (use 0.08206 for R). Then effective M = i*0.15 = ? Then HF ==> H^+ + F^- (H^+)=(F^-) = x (HF = 0.15-x Then x+x+0.15-x = i*0.15 Solve for x = (H^+) and %ion = (H^+)/0.15)*100 =
February 4, 2015

Chemistry
And changing your names makes things harder for us to do a good job for you.
February 4, 2015

Chemistry
I have a Ph.D. in chemistry. That Dr in front of Bob222 is real. Why would I answer a question in which I wasn't sure of the answer (but yes, I sometimes makae mistakes)? You are answer shopping. What you are doing is taking a vote on which is the best answer? Basically ...
February 4, 2015

Chemistry
I answered both of these below. If you don't like those answers you need to be more specific about what you want in the answer.
February 4, 2015

chem
I've been out more than 50. I know how he feels.
February 4, 2015

chem
Probably it isn't a trick question. p1v1 = p2v2 You know p1 and v1 and p2, solve for v2.
February 4, 2015

Chemistry
Don't overload the column
February 4, 2015

Chemistry
The packing material cracks (gooves/channels form) and this results in poor separation of the mixture.
February 4, 2015

Chemistry
IO3^- + 6H^+ + 5I^- ==> 3I2 + 3H2O C6H8O6 + I2 ==> C6H6O6 + 2I^- | 2H^+ mmols KIO3 = mL x M = ? Use the coefficients in the balanced equations to convert mmols KIO3 to mmols ascorbic acid. ?mmol KIO3 x (3 mol I2/1 mol KIO3) x (1 mol I2/1 mol C6H8O6) = ?
February 4, 2015

Science
It won't stay hot forever but the reason it may not cool off as fast is that the foam cup is a better insulator than a glass cup.
February 4, 2015

chemistry
Convert 39.8m 28.2m and 4.9 ft to cm. Calculate volume = l x w x d = ? cc Convert mass using density to get mass in grams and convert to kg.
February 4, 2015

science
The water (and presumably the container too if thermal equilibrium has been attained) is hotter than the object.
February 4, 2015

Science
I thought we went over this a day or so ago. Remember momentum is conserved (in an isolated system).
February 4, 2015

Chemistry
Unbalanced. CH4(g) + O2(g) ==> CO2(g) + H2O(l) C6H12O6(s) + O2(g) ==> CO2(g) + H2O(l) Fe2O3(s) + CO(g) ==> CO2(g) + Fe(s) Fe3O4(s) + Al(s) ==> Al2O3(s) + Fe(s) CO + O2 ==> CO2 I wonder what your trouble is in predicting the products. In some cases here they told...
February 4, 2015

Chemistry
I believe #3 is wrong. The others are ok. C is a combustion reaction. D is the double displacement.
February 4, 2015

Chemistry
3 half lives in 1 hour. or about 0.333 hours.
February 4, 2015

Chemistry
2CO + O2 ==> 2CO2 When using gases one may take a shortcut and use L directly as if they were mols. 3.0 L O2 x (2 mols CO2/1 mol O2) = 3 x 2/1 = 6 L CO2 produced.
February 4, 2015

Science
I don't think so. Probably C fits better.
February 4, 2015

Chemistry
Use the Arrhenius equation and solve for Ea.
February 4, 2015

chemistry
6 definitely is true. I don't know what molecular choices they are talking about so I don't know about that.
February 4, 2015

chemistry
What's in Table I? Erxn = mass x specific heat x dT. If you assume density of the solution is the same as H2O you use 200 g for mass; otherwise if Table I contains the density use that to calculate mass of the 200 mL solution. Probably Table 1 contains specific heat; use ...
February 4, 2015

Chemistry
millimols Ce^3+ = mL x M = 60 x 0.025 = 1.5 mmols IO3^- = 40 x 0.045 = 1.8 Qsp = (Ce^3+)(IO3^-)^3 = approx 9E-8 but you can do the more exact number. Note that M = mmols/mL. which means Ksp will be exceeded and a ppt will form. Now we must find the limiting reagent. Ce^3+ + ...
February 4, 2015

chemistry
It will form Ca3N2. Determine %Ca and %N and calculate the empirical formula.
February 3, 2015

chemistry
See your other post.
February 3, 2015

Science
Why not calculate the momentum of each answer and compare with the momentum of the cheetah instead of guessing?
February 3, 2015

Science
Yes, for every action there is an equal and opposite reaction. Water goes one way, jelly fish goes the other. Same way jet airplanes fly except they don't use water but the blast of hot gases from the engines.
February 3, 2015

chemistry
You may be just a 9th grade student but from what you wrote above you know a good bit of the chemistry involved. You determine the percent composition (meaning determine %Ca and %N) and use those numbers to calculate the empirical formula. 9th grade chemistry does that all the...
February 3, 2015

chemistry
Close and I thought of that at the beginning; however, I don't think that PROVES it is Ca3N2. It gives some strong hints but I don't think it proves it. For example, Mg3N2 will do all of what you describe, too. Mg3N2 reacts with H2O to form Mg(OH)2 which is highly ...
February 3, 2015

chemistry
How advanced is this course? I don't think any of the following answers will do because I assume this is a beginning course; however, 1. Determine the crystal structure by x-ray crystallography. 2. Some information can be obtained by infrared spectroscopy. 3. Determine the...
February 3, 2015

Chemistry
I agree it is a little confusing as to exactly what they want. In particular the pH range of the average range is confusing but I would go with the average percent or (0.057+0.084)/2 = about 0.0705%. I would start with 100 mL of solution and that will contain 100 x 0.000705 = ...
February 3, 2015

Acidity of different concentrations
Yes and yes. Yes, the concentration affects the pH and the pH of a stronger acid will have a lower pH.
February 3, 2015

Chemistry
q = mass ethanol x specific heat ethanol x (Tfinal-Tinitial)
February 3, 2015

Organic Chemistry TLC Chromatography
I don't know how this fits into TLC chromatography but here is what I would do. 5.6 mL x 0.95% = mL x 85% mL = 6.2588 mL is what you can make. So you take 5.6 mL 95:5 ethyl acetate and add pure ethyl acetate to make 6.2588 mL total. Check it. You have 5.6 mL x 0.95 = 5.32 ...
February 3, 2015

Chem Uni. Urgent!!!
I re-iterate that the percent recovery is not 50%.
February 3, 2015

Chem Uni. Urgent!!!
So you had in that 1g of stuff you started with 1 x 0.85 = 0.85g acetanilide; 1 x 0.14 = 0.14g NaCl; 1 x 0.01 = 0.01 g charcoal. Wouldn't the theoretical yield = 0.85 g acetanilide. That's what you would get if you had 100% yield? right? I might argue that percent ...
February 3, 2015

Science
Yes.
February 3, 2015

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