chem: mole calculation(15 pts)

1.) 5.2 g of zinc was heated with 250cm³ of dilute hydrochloric acid containing 18 g of hydrogen chloride per dm³ . Calculate the mass of zinc left.

Zn + 2HCl → ZnCl2 + H2
Mole ratio Zn : HCl = 1 : 2

Mass of HCl used = 18 x (250/1000) = 4.5 g
Molar mass of HCl = 1 + 35.5 = 36.5 g/mol
No. of moles of HCl used = 4.5/36.5 = 0.1233 mol
No. of moles of Zn reacted = 0.1233/2 = 0.0617 mol
Mass of Zn reacted = 0.0617 x 65.4 = 4.0 g

Mass of Zn left = 5.2 - 4.0 = 1.2 g


2.) Find the percentage by mass of hydrogen chloride contained in a 1.5 M hydrochloric acid .Given that the density of the acid is 1.026 g cm^-3 .

Consider 1 dm³ (1000 cm³) of the 1.5 M hydrochloric acid.
Mass of 1.5 M hydrochloric acid = 1000 x 1.026 = 1026 g
No. of moles of HCl = 1.5 x 1 = 1.5 mol
Mass of HCl = 1.5 x (1 + 35.5) = 54.75 g

% by mass of HCl = (54.75/1026) x 100% = 5.34%