Question

A 55 g sample of impure zinc reacts with exactly 129 cm3 hydrochloric acid which has a density of 1 .18 g/cm3 and contains 35.0% HCl by mass. What is the percent metallic zinc in the sample? assume the impurity is inert to HCl. Please show all work and the answer.

Answer 1

the reaction is

Zn + 2HCl ---> ZnCl2 + H2

we know that

mass = density x volume

given

density = 1.18

volume = 129

so

mass of HCl sample = 1.18 x 129

mass of HCl sample = 152.22 g

now

% mass = mass of HCl x 100 / mass of HCl sample

so

35 = mass of HCl x 100 / 152.22

mass of HCl = 53.277 g

now

we know that

moles = mass / molar mass

so

moles of HCl = 53.277 / 36.461

moles of HCl = 1.461207528

now

consider the reaction

Zn + 2 HCl --> ZnCl2 + H2

we can see that

moles of Zn reacted = 0.5 x moles of HCl

so

moles of Zn reacted = 0.5 x 1.461207528

moles of Zn reacted = 0.730603763

now

mass = moles x atomic mass

so

mass of Zn = 0.730603763 x 65.38

mass of Zn = 47.767

now

% Zn = mass of Zn x 100 / mass of sample

so

% Zn = 47.767 x 100 / 55

% Zn = 86.85

so

percent metallic zinc in the sample is 86.85 %