Wednesday
August 27, 2014

Posts by DrBob222


Total # Posts: 43,373

chemistry
1.00 what? grams? molar? L?
April 28, 2014

chemistry
delta T = Kb*m Solve for delta T and add to 100 C to find the new boiling point.
April 28, 2014

chemistry
total mols = mols toluene + mols cholesterol mol fraction toluene = X = mols toluene/total mols. The ptoluene = Xtoluene * Potoluene
April 28, 2014

chemistry
Balance the equation. N2 + 3H2 ==> 2NH3 Using the coefficients in the balanced equation, convert mols N2 to mols H2. Then convert mols H2 to g. g = mols x molar mass.
April 28, 2014

Chemistry
I wonder if that is [UO2]^2+? U^4+ ==> UO2^+ Here is how I do it which is not the short way. Oxidation state of U on left is +4. On right is +5. Balance the change in oxidation state by adding electrons to the appropriate side. U^4+ ==> UO2^+ + e Count the charge on the ...
April 28, 2014

Chemistry
The half reactions are Cu(s) ==> Cu^2+ + 2e (you had 1+ for Cu) O2(g) + 4e ==> 2O^2- (you can see how this differs from what you had). The Cu is the oxidation half; O2 is the reduction half.
April 28, 2014

Chemistry
I don't think it will but it might be wise to try it on a small scale in the lab before taking a chance on a large scale.
April 28, 2014

Chemistry
2C2H6 + 7O2 --> 4CO2 + 6H2O dGrxn = (n*dGo products) - (n*dGo reactants)
April 28, 2014

Simple Chemistry
a. How many mols do you want? That's M x L = 0.150 x 0.250 = ? Then mols = grams/molar mass. You know molar mass and mols, solve for grams CoCl2. Add that many g CoCl2 to a 250 mL volumetric flask, add a little water, swirl until dissolved, make to the mark with distilled ...
April 28, 2014

Chem
See your other post.
April 28, 2014

Chemistry
I don't get 5.04 for K but you're on the right track. -4010 = 8.413*298*lnK K = ? I obtained approx 0.2 Then ...........A + B ==> C I.......0.30.0.40...0.0 C.........-x...-x....x E.....0.30-x..0.40-x..x Substitute the E line into Kc expression and solve for x, then ...
April 28, 2014

Chemistry URGENT/DR BOB
See your other post.
April 28, 2014

Chemistry URGENT
mass soln = mass solvent + mass solute unless it is a density problem and that is mass = volume x density
April 28, 2014

Chemistry URGENT
I will make some assumptions for #2. That the 85.5 g solubility you quote later is 85.5g BaCl2/100 g water @ 60 C. If that's so then you will be able to dissolve 85.5g x (150gH2O/100 gH2O) = approx 128 g BaCl2 that can be dissolved at 60 C. The only piece of information ...
April 28, 2014

Chemistry URGENT
#1. Take the solubility at 30 and subtract solubility at 20 and divide by 10. That gives you an average solubility per degree C. You have it at 20, then add 3*solubility/degree and you will have it at 23 c. #2. Surely you have a solubility curve or a graph that will tell you ...
April 28, 2014

Chemistry
You mean name three? There are literally hundreds. Solutions of NaOH, HCl, NaCl, Na2CO3, Na2SO4 etc etc and all of these are STRONG electrolytes (not weak electrolytes).
April 28, 2014

problem solving
If the picture is square then it must be sqr6 3600 = 60 cm each edge. If the picture frame is 5cm wide, and assuming no overlap between the picture and the frame, the total length of frame + picture is 60 + left side frame + right side frame = 70 cm. The perimeter is the ...
April 27, 2014

Chemistry
Andrea, Luke, you want a secnod opinion?
April 27, 2014

Chemistry
Both are effective as far as neutralization of acids but NaHCO3 is mild enough that humans can tolerate it; NaOH will cause serious issues with the body especially in stronger doses.
April 27, 2014

chemistry
Aren't these the same problem? You didn't look to see your old post? http://www.jiskha.com/display.cgi?id=1398649923
April 27, 2014

chemistry
HCl + NaOH ==> NaCl + H2O mols NaOH = M x L =? Using the coefficients in the balanced equation, convert mols NaOH to mols HCl. Then M HCl = mols HCl/L HCl. Solve for M HCl.
April 27, 2014

Chemistry
Use PV = nRT P in kPa V in L n = grams/molar mass R = 8.314 T = kelvin = 273+C
April 27, 2014

Chemistry
I would assume a convenient number for the rate of Xe, say something like 5 L/min. Then rate unknown gas, x, is 1.86*5. (rate x/rate Xe) = (MM Xe/MM X) Solve for MM = molar mass X.
April 27, 2014

Chemistry
Use PV = nRT and solve for n = number of mols. Then n = grams/molar mass. You know n and grams, solve for molar mass. Don't forget P is in atm, V in L and T in kelvin
April 27, 2014

science/ ms. sue
The oil reduces the friction between the two metal pieces.
April 27, 2014

Chemistry
q = mass x specific heat x (Tfinal-Tinitial)
April 27, 2014

Chemistry
Use PV = nRT and solve for n = number of mols in the cylinder. Do the same and solve for n in the smaller balloons. Then determine how many can be filled.
April 27, 2014

chemistry
A. It isn't a stupid website. B. They aren't stupid questions. C. You see by looking. Use your eyes, not your keyboard.
April 27, 2014

Chemistry
If it's still in that 48.0 L container the volume will be, guess what, 48.0L. I assume you are asking what volume if the gas were allowed to expand freely but the question isn't clear on that. (V1/T1) = (V2/T2) Remember T must be in kelvin.
April 27, 2014

chem
1 mol C5H11OH contains 12 mol H atoms. Each mol contains 6.02E23 individual atoms so 12 mols will contain ....... atoms.
April 27, 2014

chemistry
Hi back. If you have a question post it at the top of the page.
April 27, 2014

chemistry
a. joules H2O absorbed = mass H2O x spcific heat H2O x (Tfinal-Tinitial) b. joules absorbed by H2O = heat gained by metal d. q metal = mass metal x specific heat metal x (Tfinal-Tinitial) c. q = mass metal x delta T
April 27, 2014

Chemistry
I worked this for you a few days ago. Did you not see it? not understand it? Show your work that you've done and we can go from there. The empirical formula is C8H20Pb
April 27, 2014

Chemistry
K = (NH3)^2/(N2)(H2)^3 You know N2 and H2, substitute with Kc and find NH3 in M = mols/L. Then to find mols in 10L, that is mols = M x L Then mol = grams/molar mass. You know molar mass and mols, solve for grams.
April 27, 2014

Chemistry
.........M2X3 ==> 2M^3+ + 3X^-2 I.......solid.....0........0 C.......solid.....2x.......3x E.......solid.....2x.......3x Ksp = (M^3+)^2(X^2-)^3 Ksp = (2x)^2(3x)^3 Substitute and solve for Ksp.
April 27, 2014

chemistry
Pb^2+ + C2O4^2- ==> PbC2O4 CrO4^2- + Cu^2+ ==> CuCrO4 As^3+ + S^2- ==> As2S3 you balanced
April 27, 2014

Chemistry
There isn't anything here to be confused about. ............PCl5 --> PCl3 + Cl2 E.........0.00500..0.00680..0.0290 What's K. Kc = (PCl3)(Cl2)/(PCl5) Plug in the equilibrium numbers and solve for Kc.
April 27, 2014

chemistry
How much of this can you do? A seems easy enough. What do you have for that? B. What's the mol count? C. What's the ideal gas law and what do you plug into it?
April 27, 2014

Chemistry
Your post isn't clear.
April 27, 2014

chemistry
I'm glad you understand it. I don't know when I've screwed a simple problem up so badly and it all goes back to writing the equation incorrectly. Let that be a lesson. Make sure the equations you work with are balanced.
April 26, 2014

sorry about that---chemistry
I typed the wrong equation in so I'm wrong too. Here is how it goes. 2H2 + S2 ==> 2H2S Kc = (H2S)^2/(H2)^2(S2) Kc = (0.24666)^2/(0.2933)^2(0.1333) Kc = 5.3057 You have in the original problem, assuming you typed in all the digits, 4.4, 2.0 and 3.7 and 15.0. That allows ...
April 26, 2014

oops again---chemistry
Sorry. I shouldn't have type the oops in the first place. The reaction is H2 + S2 ==> 2H2S Kc = (H2S)^2/(H2)(S2) Kc = (0.24666)^2/*0.29333)(0.1333) You square the H2S because the coefficient is 2. You raise (H2) and (S2) to the first place since the coefficient for both...
April 26, 2014

oops--chemistry
I forgot the square on H2. That should be K = (0.24666)^2/(0.2933)(0.1333)^2
April 26, 2014

chemistry
So K = (0.24666)^2/(0.2933)(0.1333) = Punch in the top numbers and divide by the bottom numbers WITHOUT copying any numbers; i.e., leave everything in the calculatord come up with an answer. I don't get 39.
April 26, 2014

chemistry
What numbers do you get for 4.4/15 = ? 2/15 = ? 3.7/15 = ?
April 26, 2014

chemistry
And your answers were?
April 26, 2014

chemistry
What numbers did you substitute for concns H2, S2, H2S? That should be (H2) = 4.4/15 = ? (S2) = 2/15 = ? (H2S) = 3.7/15 = ? I suspect that's the problem.
April 26, 2014

chemistry
M each = mols/L = ? Substitute M of each into the Keq expression for H2 + S2 ==> 2H2S and solve for Keq.
April 26, 2014

Chemistry 2
You also listed Ka wrong. That's 1.8E-5. acetic acid is HAc = HC2H3O2 millimols HAc = mL x M = 30 x 0.1 = 3 millimols NaOH = 3 ........HAc + NaOH ==> NaAc + H2O I.......3.......0........0.....0 add.............3............. C......-3......-3........3......3 E.......0...
April 26, 2014

Chemistry 2
If this is a mixture you didn't post all of the problem.
April 26, 2014

oops---Chemistry
I might believe 8 days but not 8 min.
April 26, 2014

Chemsitry
A--> 2B Kc 2B --> A K'c = 1/Kc
April 26, 2014

Chemistry
Yes but that's too many significant figures.
April 26, 2014

Chemistry
Several things can change the equilibrium (shift to left or right) but only change in T can change the numberical value of Kp or Kc.
April 26, 2014

Chemistry URGENT
#2 is right. #1 I'm unsure exactly what is being asked. I think I responded to this question within the last few days but I interpreted the question then as being one of accuracy/precision of weighing. I thought they were after the precision of balances et al. I don't ...
April 26, 2014

Chemistry URGENT
I can't believe the numbers are right for all entries. For example, when I look at 23410.2-21789.6 for mass after first heating ( a loss of 1620.7) then loss after second heating of 2116.6 that's 21789.8-2116.6 = that's 19,673.2 which is unbelievable between ...
April 26, 2014

chemistry
2HCl ==> H2--not balanced mols H2 needed = grams/molar mass = 200/2 = 100 mols So you will need 200 mols HCl. g HCl = mols HCl x molar mass HCl
April 26, 2014

Chemistry URGENT
If things are what you show then mass NaCl is 5.0000 and the extra zeros are necessary to show the number of significant figures. There is no indication for the use of the 8.4 nor the units.
April 26, 2014

chemistry URGENT
Both student A and student B get a 100 for accuracy. If the correct value is 2.63 and both obtained 2.63 then both are about as accurate as you can get. I would suggest that errors for both are random but I don't think you can tell that from the data. I think random errors...
April 26, 2014

chemistry URGENT
I think you are right with #1. I can't answer 2 and 3 because I don't know the correct value.
April 26, 2014

chemistry
I think you meant to say the freezing point depression constant is -1.86 degree C/m for water. (The normal freezing point is 0.00 C) mols Na2SO4 = grams/molar mass = approx 0.035 but you need to do it more accurately. molality = mol/kg solution = approx 0.035/0.045 = approx 0....
April 26, 2014

Chemisrty
See your other post.
April 26, 2014

oops--Chem
I did work it; however, I didn't post it. Here is is. http://www.jiskha.com/display.cgi?id=1398473570
April 25, 2014

Chem
I did work it; however, I didn't post it. Here is is.
April 25, 2014

Chem
I worked this for you earlier. I'll look for it if you can't find it.
April 25, 2014

chemistry urgent!
Reactions go to completion for one of just a few reasons. 1. A ppt (insoluble material) is formed. You need to know the solubility rules to know what is soluble and what isn't. Here is a simplified table. http://en.wikipedia.org/wiki/Solubility_chart 2. A gas is formed. (...
April 25, 2014

College Chemistry
I worked this earlier today but with different numbers. 3.00 mols NaCl mols AgNO3 = M x L = 0.9L x 0.5M = 0.45 .........AgNO3 + NaCl ==> AgCl I.......0.45..................... add.............3.00............ C.......-0.45..-0.45......+0.45 E.........0.....2.55.......0.45 ...
April 25, 2014

Chem
H2A + 2NaOH ==> Na2A + 2H2O mols NaOH = M x L = ? mols H2A = 2 x mols NaOH from the coefficients in the balanced equation. mols H2A = grams H2A/molar mass H2A
April 25, 2014

Chemistry
Same procedure. mols HCl = grams/molar mass Then M = mols/L solution.
April 25, 2014

Chemistry
In what units? molarity? 27.08 what? grams? mol = grams/molar mass Then M = mols/L solution.
April 25, 2014

Chemistry
NH4Cl + Na2SO3 no reaction NH4Cl + NaOH --> NH3 + H2O + NaCl Na2SO3 + BaCl2-->BaSO3 + 2NaCl Na2SO3 + NaOH -->I don't believe this will react. H2SO4 + BaCl2-->2HCl + BaSO4 BaCl2 + 2NaOH -->Ba(OH)2 + 2NaCl
April 25, 2014

chemistry
You want 315 mL of 0.620M = 0.315*0.620 = mols ethanol needed. mol = g/molar mass to give you grams, then use the density to calculate volume (mL) ethanol. Then to make this solution, you must add H2O to make a total volume of 315 mL.
April 25, 2014

chemistry
This isn't any chemistry I've seen. You want to make $1000 in sales (Is that in 1 month?). At $100 each you must sell 10 to get the $1000. The machine needs 6 parts for a product so you must have 10*6 = 60 parts. 10 workers can make 39 parts in a month so you need 60 ...
April 25, 2014

chemistry
AgNO3 + NaCl ==> AgCl(s) + NaNO3 You start with 3.0 mols NaCl. Add 200 mL x 1.5M AgNO3 = 0.300 mols. You will form 0.3 mols AgCl. You will have 2.7 mols NaCl unreacted.
April 25, 2014

Chemistry
If you added 18.01 mL of 0.1M NaOH you added 0.01801 x 0.1 = ? mols NaOH Then (NaOH) = mols/L = 0.001801/0.02801 = ? You may have added 0.4503 mols for all I know since you posted only part of the experiment, but mols NaOH in that particular part is 0.1 x 0.0180 = ?
April 25, 2014

Chemistry
You added how may mols NaOH? That's M x L = mols. What final volume do you have. You added 18.01 mL and 10 mL so total volume is 28.01 mL. Convert that to L., then M = mols/L
April 25, 2014

Chemistry
I don't know the question. Could this be the molar mass they want? Molar mass MgNH4PO4.6H2O is 245.4.
April 25, 2014

Chemistry. Please
mols H2SO4 = M x L = ? mols Mg(OH)2 = mols H2SO4 (from the coefficients in the balanced equation). Mg(OH)2 + H2SO4 ==> MgSO4 + 2H2O
April 25, 2014

Chemistry. Please :(
1. What combustion reaction? 2. W + 2H2C2O4 ==> W(C2O4)2 + 2H2 Note: I would not think the above is the correct formula for tungsten oxalate but this was the only reference I could find. 3 mol W x (2 mol H2/1 mol W) = 6 mols H2 gas. mass = mols H2 x molar mass H2.
April 25, 2014

Chemistry
You have the equilibrium pressures, calculate Kp, then dGo = -R*T*lnK
April 25, 2014

Chemestry
How many g Na2SO4 do you have?
April 25, 2014

Chemistry
The problem doesn't tell us what the reaction is; i.e., is this K for A + B ==> C or for C ==> A + B. I am assuming it is for A + B ==> C Use dG = -RT*lnK and solve for Kc. Then .............A + B ==> C I..........0.30.0.40....0 C...........-x...-x.....x E...
April 25, 2014

Chemistry
For #2, I assume you have tables. HCl(l) ==> HCl(s) dSrxn = dSproduct - dSreactant That will give you dS/mol, then multiply by 5.20 mols.
April 25, 2014

Chemistry
dG = dH-TdS. At the melting point, dG = 0 (dG always 0 at equilibrium conditions) rearrange to dS = dH/T.. Boiling point don the same way but substitute dHvap for dHfus and different T.
April 25, 2014

Chemistry
That looks ok to me.
April 25, 2014

Chemistry
Q is the same form as K; i.e., concentrations in M of products over concentrations in M of reactants and raise each reagent to the power shown by the coefficients. In this case, you're dealing with pressures so it's partial pressure instead of concentrations. In other ...
April 24, 2014

Chemistry
dG = dGo + RTlnQ
April 24, 2014

Chemistry
dGrxn = dGo + RTln Q
April 24, 2014

Chemistry URGENT
The answer to A depends upon what kind of accuracy/precision you are looking for. I think 0.2 to 0.3 mg is pretty standard. So I would go with 3.0662 - 0.0002 = ? or on a bad day 3.0552-0.0003 = ? Frankly, that is in the neighborhood of 7% error and that isn't great but it...
April 24, 2014

chemistry
It appears to me that the answer is -0.268 kJ. The problem wants the answer in J which is -268 and in scientific notation that is -2.68E2 (without the J unit).
April 24, 2014

chemistry
What have you done those three times? Are you to calculate this from dG = dH - TdS or from standard S tables.
April 24, 2014

chemistry
You need to find the caps key on your keyboard and use it. What kind of concentration. Since you've listed grams solution instead of L of solution, you need the density or grams solvent. In any case you need mols K2SO4 and that is grams/molar mass.
April 24, 2014

chemistry
It would help if you asked a question. There is none here. Do you want grams MgCl2? If you have 0.050 kg solution that is 0.050 kg x (1000g/kg) = 50 g solution. If that is 4% MgCl2, then 50g solution x 0.04 = 2 g MgCl2
April 24, 2014

Chemistry
millimols KF = 1000 mL x 0.1M = 100 millimols HF - 1000 nK x 0.25 = 250 mmols KOH added = 54 .......HF + OH^- ==> F^- | H2O I......250...0......100 added.......54............... C......-54.-54.......+54 E......196...0........54........ Then pH = pKa + log (base)/(acid) ...
April 24, 2014

Chemistry
p*molar mass = density x R*T P is is atm or 779/760 = ? R = 0.08206 L*atm/mol*K T = 25C = 298 kelvin
April 24, 2014

Chemistry
You substituted M - 0.65 for acid, therefore, the 0.118 you have calculated is molarity acetate ion. M = mols/L 0.118 = mols/5.00 mols = 0.591 This is your error. grams = mols x molar mass or 0.591 x molar mass = ?
April 24, 2014

Chemistry
How much do you know about this. Post your work so far and tell us what your sticking point is.I can help you through it.
April 24, 2014

Chemistry
I worked this for you a day or so ago. Find that and you have it. Or post your work here and I can show you where you're going wrong.
April 24, 2014

Chemistry
Use the Henderson-Hasselbalch equation. Post your work if you get stuck.
April 24, 2014

chemistry
Use PV = nRT and solve for n = number mols HCl. The M HCl = mols HCl/L solution. Then pH = -log(HCl)
April 24, 2014

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