Calculate the percent by mass.

Question

Calculate the percent by mass of zinc in the post-1982 pennies using the following information: the total mass of each penny is 2.500 g, the density of copper is 8.96g/mL, the density of zinc is 7.14g/mL, and the mass of a penny if it were 100% copper would be 3.11g.

Answer 1

Let's find the volume of the penny first.

3.11 g x 1 ml/8.96 g = 0.347 mls

let x = mls Cu

let 1-x = mls Zn

(8.96 g/ml)(x mls Cu) + (7.14 g/ml)(1-x mls Zn) = 0.347 ml

solve for x and multiply it by 8.96 g/ml to get g of Cu and divide that by 2.500 g to get % Cu

Subtract %Cu from 100% to get % Zn