Question

A piece of brass ( alloy of copper and zinc) weighs 12.9 gram in air. When completely immersed in water it weighs 11.3 gram. What is the mass of copper contained in the alloy. Relative densities of copper and zinc are 8.9 and 7.1 respectively

Answer 1

The mass of copper in the alloy is 7.614 gms.

Explanation:

Mass of water displaced = 12.9 - 11.3 = 1.6 g

=> volume of water displaced = mass / density = 1.6/1 = 1.6

we know that relative density = density of substance / density of water

Since density of water = 1

=> density of copper = 8.9

let the mass of copper in 12.9 grm of allow is x

So water displaced by the copper portion of alloy = x/8.9

Similarly,

density of zinc = 7.1

and mass of zinc in allow = 12.9 - x

=> water displaced by zinc = (12.9- x)/7.1

Hence total water displaced by the alloy,

x/8.9  +  (12.9-x)/7.1   = 1.6

Solving we get,

x = 7.614 gms

Hence mass of copper in the alloy is 7.614 gms.

Answer 2

Answer:

The answer is 7.61grams