Question

To make a saturated solution, 36 g of sodium
chloride is dissolved in 100 g of water at 293 K. Find
its concentration at this temperature.
​

Answer 1

Mass of solute = 36 g

Mass of solvent = 100 g

∵ Mass of Solution = Mass of Solvent + Mass of Solute,

∴ Mass of Solution = 100 g + 36 g = 136 g

We know,

w/w% concentration = (Mass of Solute)/(Mass of Solution) × 100%

∴ Concentration = (36 g)/(136 g) × 100%

⟹ Concentration = 0.264 × 100%

⟹ Concentration = 26.4%. (Answer.)

More:-

• w/v% of concentration = (Mass of Solute)/(Volume of Solution) × 100% — Usually used in Pharmacies and Medical purposes.
• v/v% of concentration = (Volume of solute)/(Volume of Solution) × 100%.

Answer 2

As we can see in the question, the mass of solute and mass of solvent is given in the question. So, we will have to calculate the mass percentage of the solution.

Also, we should know about what the saturated solution is. It is a solution at which the maximum amount of solute can be dissolved under the particular temperature and pressure at which the solution exists.

Mass Percentage:

When the mass of both the solute and the solvent is given in grams, it is always convenient to express the concentration in terms of mass percentage.

Mass of solute (sodium chloride) =36g

Mass of solvent (water)= 100g

Percent by $Mass =\dfrac{\text{Mass of Solute}}{\text{Mass of Solvent}}\text{x 100}$

Therefore, $Concentration of solution =\dfrac{36}{126}\text{x100} =\dfrac{36}{126}\text{x100} =26.47% (w/w)$

As per the given calculation, the concentration of this saturated solution at this temperature= 26.47%.

Also, if temperature increases, solubility also increases and if it decreases solubility also decreases. It infers that solubility is directly proportional to the temperature.