1. Hydrogen Collection Over Water
14.23 mL of H2 gas is produced at 23.5C by the following reaction. If atmospheric pressure is torr, how much Zn(s) is consumed?
Reduction
Oxidation
2 HCl(aq) Zn(s)  ZnCl2(aq) H2(g)
65.39
T = _____
23.5C
H2(g)
gramsZn
H2O(g)
V = _____
14.23 mL
MolesZn
P = _____ ?
n = _____
Problem: The pressure in the collection tube is due to both H2O(g) and H2(g)
HCl(aq)
We need the pressure of H2(g)
Zn(s)

2. Dalton’s Law of Partial Pressures
Total Pressure
H2 Partial Pressure
H2O Partial Pressure =
Ptot = PH PH2O
i.e. the total pressure is also ATMOSPHERIC PRESSURE
Patm = PH PH2O
Rearrange.....
PH = Patm PH2O
748.2 torr (barometer)
More Info Required

3. Partial Pressure of H2O @ 23.5 C (Provided on Exams)
T= 23C PH2O = 21.1 torr
T= 24C PH2O = 22.4 torr
T= 23.5C
PH2O = torr
P = 1.3 torr
1.3 torr 2
= torr
PH2O = 21.1 torr torr = torr

4. Dalton’s Law of Partial Pressures
Total Pressure
H2 Partial Pressure
H2O Partial Pressure
Ptot = PH PH2O
i.e. the total pressure is the sum of all non-reactive gas partial pressures.
Total pressure = atmospheric pressure
Patm = PH PH2O
PH = Patm PH2O -
748.2 torr (barometer)
21.75 torr
More Info Required
PH = torr

5. Hydrogen Collection Over Water
65.39
2 HCl(aq) Zn(s)  ZnCl2(aq) H2(g)
T = _____
23.5C
H2(g)
gramsZn
H2O(g)
V = _____
14.23 mL
MolesZn
P = _____
torr
n = _____
Problem: The pressure in the collection tube is due to both H2O(g) and H2(g)
HCl(aq)
We need the pressure of H2(g)
Zn(s)

6. Hydrogen Collection Over Water
65.39
2 HCl(aq) Zn(s)  ZnCl2(aq) H2(g)
T = _____
23.5C K
H2(g)
3.664  10-2
gramsZn
H2O(g)
V = _____ L
14.23 mL
 10-4
MolesZn
atm
P = _____
torr
n = _____
 10-4
mols
1 mol Zn: 1 mol H2
n =
P V
R T
( atm)
( L) =
( (L atm)/(mol K))
( K)
HCl(aq)
n =  10-4 moles H2
Zn(s)