What volume of copper (density 8.96 g/cm3) would be needed to balance a 2.52 cm3 sample of lead (density 11.4 g/cm3) on a two-pan laboratory balance?

Question

What volume of copper (density 8.96 g/cm3) would be needed to balance a 2.52 cm3 sample of lead (density 11.4 g/cm3) on a two-pan laboratory balance?

Answer 1

Your goal here is to have the same number of grams on each side of the balance.

Density (g/cm3) = mass (g) / Volume (cm3) ; therefore mass = density x Volume.

Since we want the masses of copper and lead to be equal, we can use the above equation for each to get:

(density of copper)x(Volume of copper) = (density of lead)x(Volume of lead) ; plug numbers in

(8.96 g/cm3)x(Volume of copper) = (11.4 g/cm3) x (2.52 cm3) ; multiply the right side and divide by 8.96 on both sides

Volume of copper = 3.21 cm3

Logic Check: Since copper is less dense, it makes sense we would need more of it to have the same mass.