Question

Hydrogen gas produced in the laboratory by the reaction of zinc and hydrochloric acid was 23) collected over water at 25°C. The barometric pressure at the time was 742.5 mm Hg. What is the pressure of dry hydrogen gas if the vapor pressure of water at 25'C is 23.8 mm Hg?
A) 760.0 mm Hg
B)718.7 mm Hg
C)742.5 mm Hg
D) 766.3 mm Hg
E) none of the above

Answer 1

Answer:

Explanation:

The balanced chemical reaction is:

$Zn+2HCl\rightarrow ZnCl_2+H_2$

According to Dalton's law, the total pressure is the sum of individual pressures.

$p_{total}=p_1+p_2$

As the hydrogen is collected over water, the total pressure will be sum of pressure of water and pressure of dry hydrogen.

$p_{total}=p_{H_2}+p_{H_2O}$

$p_{total}$ = 742.5 mm Hg

$p_{H_2}$ = ?

$p_{H_2O}$ = 23.8 mm Hg

Putting in the values:

$742.5=p_{H_2}+23.8$

$742.5-23.8=p_{H_2}$

$p_{H_2}=718.7mmHg$

Thus the pressure of dry hydrogen gas is 718.7 mm Hg