Question

What mass of KCl will produce a saturated solution in 500.0g of water at 20°C? The molar solubility of KCl at this temperature is 0.456 mol/100.0g

Answer 1

Given:

Weight of water used= 500g

Temperature= 20°C

Solubility = 0.456mol/100g

To Find:

mass of KCl (solute) used = m =?

Solution:

We know the expression for solubility,

solubility (in g/100g) = mass of solute/mass of solvent × 100 ------(1)

Now we know the,

solubility = 0.456mol/100g, this represents that 0.456 mole of solute is able to dissolve in 100 g of solvent we can convert it into ___g/100g, by multiplying the molar mass of solute.

Thus, 0.456mol/100g = 0.456 × 74.5g/mol = 33.972 g/100g

33.972 g/100g represents that 33.972 g of solute is required per 100g of solvent to make a solution saturated at 20°C.

mass of solvent (water/H2O) = given weight = 500g

Mass of solute (KCl) = given weight = m

putting values in equation-(1)

$33.972 = \dfrac{m}{500} \times 100$

m = 169.86g

Hence, 169.86g of KCl will produce a saturated solution in 500g of water