Brass is a substitutional alloy consisting of a solution of copper and zinc. a particular sample of red brass consisting of 79.0% cu and 21.0% zn by mass has a density of 8740 kg/m3.what is the molality and molarity of zn in the solid solution?

The molality and molarity of zinc in the solution is 4.07 m and 28.11 M respectively.

Explanation:

Solute is the substance which is present in smaller proportion in a mixture and solvent is the substance which is present in larger proportion in a mixture.

We are given:

(m/m) % of Cu = 79 %

This means that 79 g of copper is present in 100 grams of alloy.

(m/m) % of Zn = 21 %

This means that 21 g of zinc is present in 100 grams of alloy.

As, zinc is present in smaller proportion. So, it is solute and copper is the solvent.

To calculate molality of the zinc, we use the equation:

where,

= Given mass of solute (Zinc ) = 21 g

= Molar mass of solute (Zinc) = 65.3 g/mol

= Mass of solvent (copper) = 79 g

Putting values in above equation, we get:

To calculate volume of a substance, we use the equation:

Density of solution =

(Conversion factors used are:  1 kg = 1000 g &    )

Mass of solution = 100 g

Putting values in above equation, we get:

To calculate the molarity of solution, we use the equation:

We are given:

Molar mass of zinc = 65.3 g/mol

Volume of solution =     (Conversion factor:    )

Mass of zinc = 21.0 g

Putting values in above equation, we get:

Hence, the molality and molarity of zinc in the solution is 4.07 m and 28.11 M respectively.