Question

A piece of brass weighs 12.9 g in air. Brass is an alloy of Zinc
and copper. When completely immersed in water it weighs
11.3 g. What is the mass of copper contained in the alloy?
Specific gravity of zinc and copper are 7.1 and 8.9
respectively.​

Answer 1

Answer:

ANSWER

Weight of brass in air = 12.9 g

weight of brass in water = 11.3 g

Weight of water displaced by brass = 12.9-11.3 = 1.6 g

Relative density of copper = 8.9= density of substance/density of water

Density f water = 1 g/cc

So, density of copper = 8.9 g/cc= Mass/ Volume

So, density of zinc = 7.1 g/cc

Volume of alloy = 1.6cc

Mass of copper in the alloy = x

Volume of alloy= Volume of copper + Volume of zinc

1.6=

8.9

x

+

7.1

12.9−x

Solving the above equation, x= 7.61 g

Answer 2

Answer:

7.61 g

Explanation:

Let :

Mass of copper in the alloy = m

= > Mass of zinc = ( 12.9 - m ) g

= > Volume of copper = m / 8.9

Volume of zinc = ( 12.9 - m ) / 7.1

Total volume of the alloy = m / 8.9 +  ( 12.9 - m ) / 7.1 .... ( i )

= > Apparent loss of weight of alloy = 12.8 - 11.3 = 1.6 g wt

Volume of water displaced by alloy = 1.6 / 1 = 1.6 cm³ ..... ( ii )

From ( i )  and  ( ii ) we get :

m / 8.9 +  ( 12.9 - m ) / 7.1 = 1.6

= > 7.1 m + 8.9 ( 12.9 - m ) = 1.6 × 8.9 × 7.1

= > m = 7.61 g

Therefore , mass of copper contained in the alloy is  7.61 g.