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July 26, 2014

Posts by DrBob222


Total # Posts: 43,174

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

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

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.

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.

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

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.

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?

Chemistry
Your post isn't clear.

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.

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 ...

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...

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

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.

chemistry
What numbers do you get for 4.4/15 = ? 2/15 = ? 3.7/15 = ?

chemistry
And your answers were?

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.

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

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.....

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

oops---Chemistry
I might believe 8 days but not 8 min.

Chemsitry
A--> 2B Kc 2B --> A K'c = 1/Kc

Chemistry
Yes but that's too many significant figures.

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.

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 ...

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 heatin...

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

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.

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...

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

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....

Chemisrty
See your other post.

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

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

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

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. (H...

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 Y...

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

Chemistry
Same procedure. mols HCl = grams/molar mass Then M = mols/L solution.

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

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

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.

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 p...

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.

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 = ?

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

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

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

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.

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

Chemestry
How many g Na2SO4 do you have?

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........

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.

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.

Chemistry
That looks ok to me.

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 ...

Chemistry
dG = dGo + RTlnQ

Chemistry
dGrxn = dGo + RTln Q

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...

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).

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

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.

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

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) Subs...

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

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 = ?

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.

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.

Chemistry
Use the Henderson-Hasselbalch equation. Post your work if you get stuck.

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

chemistry
Xgas = n gas/total mols gas.

chemistry
Let's call these r1 and r2 for reagent 1 and reagent 2. So r1 is C7H6O3 and r2 is C4H6O3. You made a typo in the equation. You typed an = sign for a + sign. C7H603+C4H6O3=C9H8O4+HC2H3O2 a. Which reactant is limiting? mols r1 = grams/molar mass = estimated 1.45 mols r2 = g/...

chemistry
Read my response. Next to last sentence. "Now convert 3 mols CH3OH to grams. g = mols x molar mass. This is the theoretical yield (that is 100% yield)."

chemistry
Which is the limiting reagent? CO + 2H2 ==> CH3OH mols CO = gram/molar mass = approx 3 mols H2 = approx 53 Convert mols CO to mols CH3OH using the coefficients in the balanced equation. That's 3 x (1 mol CH3OH/1 mol CO) = approx 3 Do the same for H2 to CH3OH. That's...

Chemistry URGENT
The balancing is ok I think but the formula are not. NaCl +AgNO3 >>> NaNO3 + AgCl(s) This is ok. BaCl2 + H2SO4 >>> BaSO4 + Cl2H(s) hydrochloric acid is HCl, not Cl2H Na2CO3 + CaCl >>> 2NaCl(s) +CO3Ca calcium chloride is CaCl2 NaOH + HNO3 >>>...

Chemistry URGENT
You asked parts of this yesterday and Bob Pursley answered. pH = -log(H^+) or (H^+) = 10^-pH So pH = 12.2 means (H^+) = 10^-12.2 and pH = 4.6 means (H^+) = 10^-4.6 and I've written them this way because that's the question and we're told to express them this way. B...

Chemistry
millimols CO3^= = 100 x 0.6 = 60 millimols Ba^++ = 500 x 0.06 = 30 ......Ba^++(aq) + CO3^=(aq) --> BaCO3(s) I......30......................... added..............60............ C.....-30.........-30............+30 E.......0..........30.............30 So this results in a co...

chemistry
Use PV = nRT. If that 1700 c means degrees celsius, don't forget to convert that to kelvin. If you are using 8.31 for R, you must use P in kPa. 1 atmosphere = 101.325 kPa.

Chemistry
I can't see the photo but a d orbital has a value of 2 for ell (I can't write the script ell and the lower case l looks like (OK, ALMOST like) the number 1).(see 1 vs l) s orbitals have ell = 0 p orbitals have ell = 1 d orbitals have ell = 2

Chemistry
(1/wavelength) = R(1/9 - 1/25) The 9 is 3^2 and the 25 is 5^2. R = 1.0973E7

Chemistry
wavelength = h/mv m = mass in kg v = velocity in m/s

Chemistry
1.29 g/cc x 25 cc x 0.381

chemistry
I think I did this last night. I would look first at calculating how much (Ag^+) must be to ppt AgCl. You have Ksp for AgCl and you have Cl- from KCl, that allows you to determine exactly how much Ag^+ is needed to ppt Agcl. Anything over that and AgCl will ppt. The question a...

Chemistry URGENT/DR BOB
All of the above looks ok to me except for these two. NaHCO3(s) + HCl(ag) >>> NaCl +2CO +H20 NaHCO3 + HCl ==> NaCl + CO2 + H2O CaCO3(s) +HCl(ag) >>> CaCl +CO3H CaCO3 + 2HCl ==> CaCl2 + H2O + CO2

Chemistry
It's one mole to one mol; therefore, how many mols do you have in 3.82 g SA? That's mols SA = 3.82g/molar mass SA. Then mols AA = mols SA and g AA = mols AA x molar mass AA

chemistry
P1V1 = P2V2

SCIENCE PPPLLLLLSSSSS HELP!!!!!!!!!!
Igneous rock becomes sediment first, then upon being deposited and compacted when other layers form on top it becomes sedimentary rock.

Chemistry
I'm not sure this has a solution since there is no way to know the mole ratio between H2 produced and mols M consumed. I have assumed +2 metal and 1mol M to 1 mol H2 ratio to make MCl2 but it may not be that at all. M + 2HCl ==> MCl2 + H2 PV = nRT P = Ptotal - pH2O = 75...

chem
Come on shadow. The q1 is to get you from ice at -33.5 to zero. The q2 is to get you from solid ice to liquid water. The q3 is to get you from zero C to 100 C. And q4 is to get you from liquid water at 100 to steam at 100. The problem asks for heat need to go from -33.5 to ste...

chem
heat needed to raise T of solid water from -33.5 to solid water at zero C. q1 = mass ice x specific heat solid ice x (Tfinal-Tinitia) where Tfinal is zero and Tinitial is -33.5 q2 = heat need to melt ice; i.e., change solid water at zero C to liquid water at zero C. q2 = mass ...

chemistry
If that's the only information available to you I would suggest that you subtract 0.265-0.247 to find how much the radius decreases from period 6 to period 5 and subtract that difference from Rb to make an educated guess at K that's down one more period.

Chemistry
Can't answer. The change in pH depends upon the kind of acid or base. Weak bases/weak acids don't change the same way as strong acids/strong bases.

chemistry
Your posting leaves a little to be desired. It's quite difficult to interpret. For this problem, use the Henderson-Hasselbalch. Substitute the numbers and solve for pH.

science-chemistry
KHP + NaOH ==> NaKP + H2O mols KHP = grams/molar mass mols NaOH = mols KHP (from the 1:1 ratio inthe balanced equation.) M NaOH = mols NaOH/L NaOH. Withthe vinegar you didn't provide enough data but it's done this way. mL vn x M vin = mL NaOH x M NaOH.

Chemistry URGENT/DR BOB
Write an equation to show how acetic acid reacts with water to produce ions in solution. C2H4O2 + H2O >>>>>>> H3O + C2H3O You need to show the charges on the ions; i.e., H3O^+ + C2H3O^- Write an equation for the neutralization of HCl and NaOH. HCl + NaOH &...

chemistry
You didn't list k1 and k2 and the numbers in my text probably don't agree with the numbers in you text.

chemistry
.....H2C2O4 ==> H^+ + HC2O4^- I....0.35M......0......0 C.....-x........x......x E....0.35-x.....x......x Substitute the E line into k1 and solve for x = (H^+) = (HC2O4^-) .......HC2O4^- ==> H^+ + C2O4^= Write the k2 expression. You've just calculated that H^+ = HC2O4...

chemistry
What's K?

chemistry
Use the second order rate equation of (1/A) - (1/Ao) = kt and solve for A at the allotted time. That will give you NO2 also. Convert to mols NO2 and mols N2O4 and use PV = nRT to solve for P. Post your work if you get stuck.

chemistry
1.1655 g/mL x 1000 mL x %NaOH x 1/40 = 4.37M. Solve for %.

chemistry
144.2 pm = 1.442E-8 cm and that's the RADIUS. volume of sphere is (4/3)*pi*r^3. See if that gets you off on the right foot?

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