When 0.40 g of impure zinc reacted with an excess of hydrochloric acid, 127 mL of hydrogen was collected over water at 10 degress C The external pressure was 737.7 Torr.

Question

a) What volume would the dry hydrogen occupy at 1.00 atm and 298 K ?

b) What amount (in moles) of H2 was collected?

c) What is the percentage purity of the zinc, assuming that all the zinc present reacted completely with HCl and that the impurities did not react with HCl to produce hydrogen? The vapor pressure of water at 10 degrees C is 9.21 Torr.

Answer 1

Zn + 2HCl ==> H2 + ZnCl2
a.
(P1V1/T1) = (P2V2/T2)
P1 = 737.7-9.21 = ?
P2 = 760
V1 = 127 mL
V2 = ?
T1 = 10 C changed to K
T2 = 298K

b.
Use PV = nRT
For P use P1 from above (convert to atm).
V use V1 from above(convert to L)
T use T1 from above (in kelvin).
Solve for n.

c.
Convert mols H2 to mols Zn.
g Zn = mol Zn x atomic mass Zn.

%Zn = (g Zn/mass sample)*100 = ?

Answer 2

85.4%

Answer 3

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