posted by Yuli on .
A student generates H2(g) over water using the reaction between zinc and hydrochloric acid
Zn(s)+ 2HCl(aq)---> ZnCl2(aq)+ H2(g)
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- lvldiff-H2O
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.
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.
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.
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?
moles Zn = grams Zn/atomic mass Zn