Question

A piece of brass weighs 12.9 g in air. When completely immersed in water it weighs 11.3 g. What is mass of copper contained in the alloy?

Relative density of copper and zinc are 8.9 and 7.1 respectively.

Answer 1

Mass of brass in air = 12.9 g

Mass of brass in water = 11.3 g

Mass of water displaced = 13.9 - 11.3 = 1.6 g

relative density of copper = 8.9

Relative density of zinc = 7.1

Relative density = density of substance/ density of water

Density of copper = 8.1 g/cc

Which can be written as Mass/ Volume = 8.1 g/cc

Similarly Density of zinc = 7.9 g/cc

and volume of alloy = 1.6 cc

Let x be the mass of copper is alloy

Hence, alloy contains the substances

Volume of alloy = Volume of copper + Volume of zinc

1.6 = x/8.9 + (12.9 - x)/7.1

1.6 = 7.1x + 8.9(12.9 - x)

x = 7.614 g

Mass of copper is 7.614 g.