Sunday
March 29, 2015

Posts by DrBob222


Total # Posts: 47,990

Science
I think your answer is right; the frequency changes as the fire truck goes by. However, I have a problem with the statement that the pitch changes from high to low as the fire truck passes by. As the fire truck comes toward you the frequency increases; after the fire truck ...
January 21, 2015

Science
right
January 21, 2015

Chemistry
This a two equation problem that you solve simultaneously. Here are the two equations. Let x = g CH4 and y = g C2H6 ---------------- equation 1 is x + y = 5.00 g You get the second equation by converting grams of CH4 to grams CO2 and grams C2H6 to grams CO2 and make the total ...
January 21, 2015

chem
3.80E25 H2O molecules x 2 = # H atoms in water molecules. 5.80E24 NH4 molecules x 4 = # H atoms in NH3 molecules. Sum is total H atoms in both sets of molecules.
January 21, 2015

Analytic chemistry
mols HgO = grams/molar mass = ? Using the cofficients in the balanced equation, convert mols HgO to mols OH^- then convert that to mols HClO4. Finally, M HClO4 = mols HClO4/L HClO4
January 21, 2015

Chemistry (Acid-Base)
This may not be the easiest way but it's what I would do. First, calculate (H^+), (butanoate), and (butanoic acid) in the 0.1 M solution at pH of 4.00. Then since I like to work in grams with these things I would convert the butanoic acid part into gram and for any number ...
January 21, 2015

AP Chemistry
No, your equation looks ok to me. I think what you need to do is to convert dG and dH from so many kJ/mol to so many kJ/4.88 g H2. To do that dG = -237.2 kJ/mol x (4.88 g/4*atomic mass H) = ? dH = -285.8 kJ/mol x (4.88 g H2/4*atomic mass H) = ? Then dG = dH - TdS You have dG ...
January 20, 2015

Chemistry
It depends upon the hydrolysis of the salt. For anions, such as CN^- in Ca(CN)2, the CN^- is hydrolyzed as follows: CN^- + HOH ==> HCN + OH^- so the solution is basic because it frees up OH^-. What about Ca^2+. It USUALLY is considered as not hydrolyzing. NaHPO4 is similar...
January 20, 2015

chemistry
You write two equations and solve them simultaneously. First equation is let x = mass NaCl and y = mass CaCl2 ---------------------- equation 1 is x + y = 12.42 The second equation you get by converting x and y to grams AgCl For NaCl(x) that is x(mm AgCl/mm NaCl) where mm is ...
January 20, 2015

AP Chemistry
Change feet to meters. Find volume in m^3. length x width x height = ? m^3 12.8 ug/m^3 x ? m^3 from above = total ug Be. Convert ug Be to g Be and convert that to mols Be. mols Be = grams Be/atomic mass Be. Then there are 6.022E23 atoms in 1 mol Be. Post your work if you get ...
January 20, 2015

Chemistry
This is a limiting reagent problem. There are other ways to do this but I like this method. Basically you work three stoichiometry problems. I will assume you will use P for phosphorus (and not P4) and P2O5 for the oxide (and not P4L10) You will need to adjust the equation if ...
January 20, 2015

AP Chemistry
..........CaF2 --> Ca^2+ + 2F^- I.........solid....0........0 C.........solid....x........2x E.........solid....x........2x The easy way to do this is to convert g/L to mols/L and go from there. mols/L = 0.0167/molar mass CaF2. Then Ksp = (Ca^2+)(F^-)^2 Ksp = (x)(2x)^2 = 4x...
January 20, 2015

AP Chemistry
Technically the CN- really is 0 initially and 2x + 0.065 at equilibrium. ......Ni(CN)2 ==> Ni^2+ + 2CN^- I.....solid........0.......0 C.....solid........x.......2x E.....solid........x.......2x Then ......KCN --> K^+ + CN^- I........0.065.....0......0 C.......-0.065....0...
January 20, 2015

Chemistry
mols NH3 = grams/molar mass = ? Using the coefficients in the balanced equation, convert mols NH3 to mols H2o Convert mols H2O to grams H2O at 100% yield. g H2O = mols H2O x molar mass H2O. Then g H2O @100%yield x 0.0611 = g H2O produced at 6.11% yield.
January 20, 2015

Chemistry
Answered above.
January 20, 2015

chemistry
28 days is 2 half lives. Start P-32 = 100% 1st half life = 1/2 that or 50% left 2nd half life = 1/2 that or 25% left.
January 20, 2015

Chemistry
Which salt?
January 20, 2015

chemistry
Please read your post and note how ridiculous it reads. The answer is that it produces zero mols NaHCO3. You start with NaHCO3. Let's suppose you asked instead to calculate the mols NaHCO3 NEEDED to react with 0.4 mols H2SO4. That's the old trick of using the ...
January 19, 2015

Earth Science
Which is why I wrote "all but b could be chosen"
January 19, 2015

Earth Science
I would chose softness as the answer for 3. All of the sites list color, luster, fracture, cleavage, hardness, streak,etc. Although we may think we know how soft a mineral is if we know the hardness, softness is not something that is measured. For #1 I agree that the answer ...
January 19, 2015

Chemistry
The easy way to do this is to work in g and A units. You know 0.5g sample x 0.240E-2 = 1.2E-3 g Cu. You know the ratio of A unit is 0.250 vs 0.6; therefore, 1.2E-3 g Cu x (.260/0.6) = ? g Cu in the unknown. To calculate molar absorptivity use A = ebc. Technically I don't ...
January 19, 2015

Chemistry
I have several issues with a). That's 1.694 mg CoSO4; when you convert that to 0.001694 that is now g/mL and not mg. Second where you have 1*10^-6 mol you threw away the other 3 places. The 1.695 is to four places and you should have 4 places in the answer. So 1.694E-3 g/...
January 19, 2015

Chemistry
Answered below twice and one time with much more information.
January 19, 2015

chemistry
mol fraction N2 = mol N2/total mols. and if you want mol fraction of the others it is XAr = mols Ar/total mols XO2 = mols O2/total mols.
January 19, 2015

chemistry
Didn't I do a similar one for you yesterday. Find total mols gase Find mole fraction (XN2) of N2. Then pN2 = XN2*Ptotal.
January 19, 2015

Chemistry
Yes to both. The weak acid and its salt (or the weak base and its salt) do not have to be the same concentration. It is best if they are because that gives you the best possible buffering capability but any reasonable values will work. Of course a VERY SMALL value for one of ...
January 19, 2015

Chemistry
I answered the similar question below. You want a weak acid and a salt of the weak acid OR a weak base and a salt of the weak base. I see no reason why this would not be a reasonably good buffer. Why don't you try it. I'll get you started. 100 mL x 0.1M HF = 10 mmols ...
January 19, 2015

Chemistry
For a buffer you want a weak acid and a salt of the weak acid (#2 answer fills the bill) or a weak base and a salt of the weak base (example is NH3 and NH4Cl). #1 is a weak acid (HF) and a salt of A weak acid (but not THE weak acid). Which Ka would you use? Ka for HF or Ka for...
January 19, 2015

analytical chem
http://web.uvic.ca/~jalexndr/192UncertRules.pdf
January 19, 2015

Anal Chem
E = experimental A = actual ------------ [(E-A)/A] = -0.054 [(2.02-A)/A] = -0.054 Solve for A
January 19, 2015

chemistry
k = 0.693/t1/2 Substitute the value of k into the below equation. ln(No/N) = kt No = 100 N = 25 k from above Solve for t in years.
January 19, 2015

science
I agree with Bob Pursley that you are/were doing it the hard way; however, the answer to your question is this. After you know mols O2 = 1.70, then you know that at STP the volume of any gas is 22.4 L for one mole. So 1.70 mols x (22.4 L/mol) = ? L.
January 19, 2015

chemistry grade 11
Probably ether but why don't you look up the vapor pressure of each at room temperature and then you will know.
January 19, 2015

Chemistry
I don't think it's a trick question. I think the thing to do is to convert all to the same units; i.e., either all H^+, all OH^-, or all pH or pOH. Let's convert all to pH. a) is pH = 3 b) is pH = 0 c) is OH^- = 10^-13 which makes pOH 13 and pH 1 d) is H3O^+= 10^-...
January 19, 2015

Science, Chemistry
What is the density of H2 gas at zdro c.? The modified gas formula is p*molar mass = density*R*T but I don't buy the density of air at STP of 14.4. 14.4 what? It's more like 29 g/L
January 19, 2015

Chemistry
If you input the = sign in the right place it is.
January 19, 2015

Chemistry (Error Propagation)
a. (5.4-3.7)+/-(0.2+0.4)
January 19, 2015

Chemistry (Electrochemistry)
One problem I had with this yesterday was that the problem quote Ti and all of the answers quote Tl. Not to same so you need to clear up that little typo.
January 19, 2015

chemistry
CH3CHCH2 + H2 ==> CH3CH2CH3 20 mL propene x (1 mol H2/1 mol propene) = 20 mL H2 consumed. There will be 50 mL H2 left.
January 18, 2015

Chemistry
B. 1 mol of gas at STP occupies 22.4L. 21.5L/22.4L = mols F2 gas. A is done the same way but use the volume occupied by one mole gas at SATP.
January 18, 2015

Chemistry
Add mols to obtain nTotal. mole fraction N2 = XN2 = nN2/nTotal pN2 = XN2*Ptotal
January 18, 2015

chemistry
(P1V1/T1) = (P2V2/T2)
January 18, 2015

Chemistry
You made a typo on the formula for iron (III) acetate. •Fe(OH)3 + 3HC2H3O2 --> Fe(C2H3O2)3 + 3H2O mols water formed = grams/molar mass = ? Convert to mols iron(III) acetate using the coefficients in the balanced equation. That will be ? mols H2O x (1 mol Fe(Ac)3/3 mol ...
January 18, 2015

Chemistry
You should be more explicit about your question; I assume you are titrating carbonate to the methyl red or methyl orange end point. The reason you boil the solution is expel the CO2 that is dissolved in the solution. During the titration you have CO3^2- + 2H^+ ==> H2CO3 ==&...
January 18, 2015

chemistry
Of course it applies. pTotal = pH2O + pH2 Look up the vapor pressure of H2O and substitute that for pH2O. I don't think everyone uses the same numbers for SATP but I will use P of 100 kPa or 0.987 atm so that is PTotal. If you looked up pH2O in mm then convert 0.987 to mm ...
January 18, 2015

chemistry
mols CO2 = mols C = 2.58/molar mass CO2 = ? mols H = 2*mols H2O = 0.53/molar mass H2O = ? mols C = approx 0.06 mols H = 0.06 ratio is 1:1; therefore, empirical formula is CH
January 18, 2015

science
When they are in line in the same direction.
January 18, 2015

chemistry
2KClO3 ==> 2KCl + 3O2 mols KClO3 = 10/molar mass KClO3 = ? Use the coefficients in the balanced equation to convert mols KClO3 to mols O2. That's mols O2 at STP = ?mols KClO3 x 3 mols O2/2 mol KClO3 = ? mols KClO3 x 3/2 = ? The use PV = nRT to convert mols O2 at STP to ...
January 18, 2015

To Devron
Since you are a biochemist please look at the post below by C. I tried answering the question but I really don't understand the question. Perhaps you can help.
January 18, 2015

Chemistry
1. What Na compound is insoluble? What nitrate is insoluble. You must have an insoluble material to use it gravimetrically. 2. You want to use Le Chatelier's Principle. An excess of the pptng solution will cause the ppt to be less soluble and that leads to more complete ...
January 17, 2015

Chemistry (Re-post)
You didn't define enough for me. Here is what I have where fn is the fraction left of the solute REMAINING in the water layer after n extractions. fn = [1+K*(Vo/Va)]-n Of course, you can calculate it three times from a single extract, too.
January 17, 2015

chemistry
Ce4+ + e− → Ce3+ Eº = 1.61 V Cu(s) ==> Cu^2+ + 2e Eº = -0.34 V Ecell = 1.61 + (-0.34) = 1.27 v You need 96,485 coulombs to deposit 1/2 gram molar mass Cu or 63. 55/2 = 31.78 g Cu. So you need 96,485 x (10.5/31.78) = ? coulombs. Convert that to Faradays...
January 17, 2015

chemistry
Oxidation is the loss of electrons. So Fe goes from +2 on the left to +3 on the right and Mn goes from +7 on the left to +2 on the right. Which loses electrons. You try writing the equations. If you have 30 mols KMnO4 you must have reacted it with 30 x 10/2 = ? and that sure ...
January 17, 2015

Chemistry
dG = dH - TdS The mistake most students make is that they don't change dS to kJ before the calculation.
January 17, 2015

Chemistry
Kudos to Devron. Very well done. Better than my answer.
January 17, 2015

Chemistry
:-). Difficult for some, yes. Dull? Never.
January 17, 2015

Chemistry
I'm a chemist and I would tell you that you're in for an exciting course; however, not every one feels that way about chemistry. Instead you must wait and see for yourself. There is some that you can memorize and if you can memorize things easily you can make it ...
January 17, 2015

Chemistry
#1. We are here to help. #2. I have no idea why you think there is an attitude problem. I'm sorry I couldn't answer your question exactly but as I stated I simply don't understand the question completely. I hoped that whatever I posted would trigger a response from...
January 17, 2015

Chemistry
I see you still think changing names helps. Here is what I think. I believe you are to calculate the pH of various solutions from pH 1 to pH 13 but I don't understand the phrase "pH titration". And I don't know how the volume fits in. I can show you how to do...
January 17, 2015

Chemistry
Would you check your problem please? Usually titration curves are done with pH vs volume. One then chooses volumes to make the curve.
January 17, 2015

Chemistry
Charlotte, Maddie, Quincy et al. I have answered this below. Changing screen names is confusing. you get better results if we can keep can follow you. Changing screen names doesn't get your questions answered any faster; in fact, it may slow the answers.
January 17, 2015

Chemistry
I have already answered this below. You may repost here if you have a follow up; it will be easier to find here than below.
January 17, 2015

Chemistry
I can't decipher what you have because of the spacing and extra lines. Do this. Write the atomic number FIRST, then the element symbol, then the mass number. For example, Radon 222 would be written as 86Rn222; the alpha particle (He nucleus) is 2He4, etc. I think you may ...
January 17, 2015

chemistry
Will you please check your post. I'm have a problem with the "higher" part. I was under the impression that C 14 content DECREASED with time, not increased.
January 17, 2015

Chemistry
Citric acid has three ionization constants; i.e., k1, k2, and k3. pK1 = 3.13 pK2 = 4.76 pK3 = 6.39 Your tables may not agree exactly; use the numbers in your text/notes. The pH you want in the solution should be as close as possible to one of the pKa values; therefore, I would...
January 17, 2015

Chemistry
Personally I think you are out of luck on someone doing this for you. Standardization of the NaOH is a chapter in itself followed by another chapter on reading the buret, preparing the buret, how to standardize the pH meter, etc. Surely you already know how to do the basics; ...
January 17, 2015

Chemistry
Distribution coefficients = Ko/a so large K values occur as the result of higher solubility in the organic phase than in the aqueous phase. In contrast, lower K values result from a higher concentration in the aqueous phase than in the organic phase. Therefore, ......can you ...
January 17, 2015

Chemistry
I would point out that a 37% w/w solution has a density of 1.19 so I wonder if you have incorrectly labeled it as v/v. It makes little difference which is true, if you don't give a volume of the hcl solution used there is no way to calculate the final concentration.
January 17, 2015

Chemistry
I don't believe the pH is absolutely necessary; however, if it is wouldn't it be pH = pKa for TRIS. Since these are equal amounts of equal concentrations then (base) = (acid) and pH = pKa + log 1 = pKa. Prepare the base by the following: mols TRIS base = M x L = 0.100 ...
January 16, 2015

Chemistry
It's a redox (oxidation-reduction) reaction and it requires an acid solution. H2SO4 usually is the acid used because HCl has complications with the chloride ion.
January 16, 2015

chemistry
2Na + Cl2 ==> 2NaCl 5.5 mols Na x (2 mols NaCl/2 mols Na) = 5.5 mols Na x 2/2 = 5.5 mols NaCl. Convert to grams. g = mols x atomic mass.
January 16, 2015

chemistry
K2CO3 + 2HNO3 --> 2KNO3 + H2CO3 then the H2CO3 decomposes as H2CO3 --> H2O + CO2 I would name that first reaction as double replacement.(some call it double displacement). Usually this reaction is written all at once as K2CO3 + 2HNO3 ==> 2KNO3 + H2O + CO2 and that ...
January 16, 2015

Science
yes
January 16, 2015

chemistry
volume of water to be removed is 5000 cm x 2500 cm x 3.2 cm = approx 4E7 cc Convert to ? L Then 5.0 L/sec x #sec = ? L. Sole for #sec.
January 16, 2015

clarify--SCIENCE
Please proof your post and make changes to make it make sense. What's AgNOS? "required 26.50 mL and Ag of AgNO3 = 0.008700g" makes no sense at all.
January 16, 2015

clarify--Chemistry - PLEASE HELP!!!
Is all 5.0 g N2O transferred to to the whipped cream container? And what is the volume of the balloon?
January 15, 2015

Chemistry
Devron is correct; this is a combustion reaction/problem.
January 15, 2015

Chemistry
T is constant so we don't need to worry about that so let's just use 300 K for it. The reaction is 2C2H2 + 5O2 ==> 4CO2 + 2H2O For the larger 7 L tank filled with O2 at a pressure of 145, what is n? Use PV = nRT and calculate n = number of moles O2. Now use the ...
January 15, 2015

CHEMISTRY
And how many books do you want me to write about these topics? If you will tell me what your trouble is in answering these I shall be glad to help you through them. What is the sticking point of each?
January 15, 2015

chemistry
Pb(NO3)2 + 2KI ==> PbI2 + 2KNO3 mols KI = grams/molar mass = ? mols PbI2 = 1/2 mols KI mass PbI2 = mols PbI2 x molar mass PbI2
January 15, 2015

Chemistry
No H bonds in CH4. NH3 is the answer.
January 15, 2015

Chemistry
Use the conversion factor. 10,000 m x (1.09 yds/1 m) = ?
January 14, 2015

Chemistry
Jefferson, what trouble are you having with limiting reagent problems. When you've worked one you've worked 98% of them. Devron showed you how to do one just a short time ago and I went through one in detail with you last night.
January 14, 2015

Chemistry
Very good. I would offer these thoughts (not suggestions). First I looked up the molar mass of Na2CO3 and obtained 105.989 but we may not have used the same sets of numbers. Second, the number of significant figures you have used is not consistent. If that 1.234 is ok then you...
January 14, 2015

Chemistry
Yes, 2 is the first equivalence point See this graph. Note the first equivalence point is HUGE compared to the third.https://www.google.com/search?q=image+H3PO4+and+NaOH&tbm=isch&tbo=u&source=univ&sa=X&ei=HCG3VJTBFJGTNuGXguAI&ved=0CCIQsAQ&biw=1024&bih=609#imgdii=_&imgrc=...
January 14, 2015

chemistry
Damon showed you how to work the problem a short way. The answer to your question is yes, it is 3*95 = ?
January 14, 2015

Chemistry
91 what? (P1V1/T1) = (P2V2/T2)
January 14, 2015

science Help
B, C and D are pure made up ridiculous answers.
January 14, 2015

Science
So half of it will be gone in 6 hours. Another half of it will be gone in 12 hours. You started with 2g. At the end of 6 hrs there will be 1 g. At the end of 12 hours there will be 1/2 g left? right?
January 14, 2015

Science
I think C is right. Speed is a scalar quantity(number only); i.e., magnitude but no direction. Velocity is a vector quantity; i.e., a magnitude with a direction.
January 14, 2015

Science
I don't think so.
January 14, 2015

Science
I agree with both.
January 14, 2015

Chemistry
This is a limiting reagent problem just like the ones that Devron worked for you this morning. 2C8H18 + 25O2 ==> 16CO2 + 18H2O That should get you started. Step 1. convert grams to mols. mols = grams/molar mass Step 2. Using the coefficients in the balanced equation, ...
January 14, 2015

Science
Radiatioin can travel through space. Conduction travels through solids and to some extent liquids.
January 14, 2015

Chemistry
Then you don't understand the question because that equation tells you everything you ever wanted to know and then some. Here is what it says. It tells you that if 4 mols Fe reacts with 3 mols O2 it will produce 2 mols Fe2O3 and 1652 kJ of heat. So the first question is 4 ...
January 13, 2015

Chemistry
I would like to add here that you had the right idea if you had followed through. Your statement that ClO is losing O is ok but since it is LOSING O is must be reduced. Gaining O is oxidation. Of course if O is nowhere in the oxidation it's tough to use that as a ...
January 13, 2015

science
When I do work, like running 1 mile in less than 4 minutes, you see heavy breathing, faster breathing, sweating, much higher heart rate, muscles tired, etc. So the work I expend in running that mile shows up as increased CO2 in the air, faster metabolism, aching muscles, etc. ...
January 13, 2015

Chemistry
IO3^- + 5I^- + 6H^+ ==> 3H2O + 3I2 I2 + 2S2O3^2- ==> SrO5^2- + 2I^- Check those equations; I'm trying to remember it instead of working it out. mol IO3^- = M x L = 0.0214 x 0.010 = ? 1 mol IO3^- = 3 mols I2 1 mol I2 = 2 mols S2O3^- Therefore, 1 mol IO3^- = 6 mols ...
January 13, 2015

chemistry
76.7g PCl3 x 0.832 = ?g PCl5
January 13, 2015

Chemistry
2 Mg (s) + O2 (g) -> 2 MgO (s) Mg on the left must go to Mg on the right but the Mg on the right is an ion. It has a charge of 2+; therefore, 2Mg --> 2Mg^2+ + 4e O2 + 4e ==> 2O^2-
January 13, 2015

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