Posted by Yuli on Thursday, November 24, 2011 at 12:14am.
A student generates H2(g) over water using the reaction between zinc and hydrochloric acid
Zn(s)+ 2HCl(aq)> ZnCl2(aq)+ H2(g)
Data:
Mass of vial and zinc 15.5082
mass of vial 15.3972
mass of zinc 0.111
final burette reading 45.30mL
barometric pressure: Patm 100.6kPa
temperature of trapped gas 24.3C
vapour pressure of water at 24.3 C: PH2O 3.004kPa
diff in solution lvls inside and outside burette 162mm H2O
I got 95.968 kPa of H2 since you said im allowed 4 sigfig i used 95.97 does that seem right?
and for the second part i got 297.5K im really not sure what am doing here the formulas i was trying to use were
atm = H2+ H2O+ lvldiff
H2= atm lvldiffH2O

chemistry  DrBob222, Thursday, November 24, 2011 at 12:45am
Let's see. I said we should take
100.6 kPa  vp H2O  water diff or
100.6  3.004  1.5876 = 96.008 kPa which rounds to 96.00 to 4 s.f. How does that stack up with the formula you are using.
atm = H2 + H2O + v or
H2 = atm  H2O  v or
H2 = 100.6  3.004  1.5876 = 96.008 and it rounds to 96.00 kPa. (I didn't use a formula; I just reasoned it out but I'm glad to see that reasoning and the formula gets the same thing. Check your math. I don't believe 95.968 kPa is correct.

chemistry  Yuli, Thursday, November 24, 2011 at 12:55am
how would you calculate the temperature of H2 in kelvin? and the moles that H2 produced? do you know a formula for that? could you please explain it to me thanks for all your help so far i've understood everything thanks to you.

chemistry  DrBob222, Thursday, November 24, 2011 at 1:20am
Your post says temperature of trapped gas is 24.3 C. In kelvin, that is 273.15+24.3 = 297.45. I would round that to 297.4; however, when I'm doing calculations, I can make "rounding" errors; therefore, I leave all of the numbers in my calculator and go to the next calculation. I also carry one more place than I'm allowed to avoid rounding errors, then round at the very end of all calculations.You can calculate moles H2 from PV = nRT. You know P now, you know V(must be in liters), you know R (it's 8.314 if you use P in kPa) and you know T in kelvin. Solve for n.

chemistry  Yuli, Thursday, November 24, 2011 at 1:52am
I did all my questions but there is this last one i don't get. Calculate the number of moles of zinc that must have reacted( assume that Zn is limiting and the yield of H2 gas is 100%) how do you do this? could you help me with this last one please?

chemistry  DrBob222, Thursday, November 24, 2011 at 12:49pm
moles Zn = grams Zn/atomic mass Zn
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