Question

The zinc within a copper-plated penny will dissolve in hydrochloric acid if the copper coating is filed down in several spots (so that the hydrochloric acid can get to the zinc). The reaction between the acid and the zinc is as follows: 2H+(aq)+Zn(s)→H2(g)+Zn2+(aq). When the zinc in a certain penny dissolves, the total volume of gas collected over water at 25 ∘C was 0.953 L at a total pressure of 752 mmHg .

Answer 1

Answer: 0.0746 grams of hydrogen

Explanation:

To calculate the mass of hydrogen :

(Vapor pressure of water is 23.78 mmHg at 25 ∘C )

$2H^+(aq)+Zn(s)\rightarrow H_2(g)+Zn^{2+}(aq)$

According to avogadro's law, 1 mole of every substance occupies 22.4 L at NTP, weighs equal to the molecular mass and contains avogadro's number $6.023\times 10^{23}$ of particles.

According to the ideal gas equation:

$PV=nRT$

P = Total Pressure = 752 mm Hg

pressure of hydrogen = Total Pressure - Vapor pressure of water =  (752 -23.78 )mm Hg = 728.22 mm Hg =  0.958 atm   (760mmHg=1atm)

V= Volume of the gas = 0.953 L

T= Temperature of the gas = 25°C = 298 K  

R= Gas constant = 0.0821 atmL/K mol

n= moles of gas= ?

$n=\frac{PV}{RT}=\frac{0.958\times 0.953}0.0821\times 298}=0.0373moles$

Mass of $H_2=moles\tims {\text {molar mass}}=0.0373mol\times 22g/mol=0.0746g$

Thus 0.0746 grams of hydrogen is collected.