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Difficulty: EasySolubility Calculations and Concentration Determination

If the solubility of sodium hydroxide (NaOH\text{NaOH}) in water at 25∘C25^\circ\text{C} is 0.50 mol/dm30.50\text{ mol/dm}^3, what is its concentration in g/dm3\text{g/dm}^3? [Na=23,O=16,H=1][\text{Na} = 23, \text{O} = 16, \text{H} = 1]

  1. 20.0 g/dm320.0\text{ g/dm}^3Answer
  2. B
    40.0 g/dm340.0\text{ g/dm}^3
  3. C
    80.0 g/dm380.0\text{ g/dm}^3
  4. D
    0.0125 g/dm30.0125\text{ g/dm}^3

Answer

The concentration of sodium hydroxide in g/dm3\text{g/dm}^3 is 20.0 g/dm320.0\text{ g/dm}^3.
To convert concentration from mol/dm3\text{mol/dm}^3 to g/dm3\text{g/dm}^3, multiply the molar concentration by the molar mass of the solute. For NaOH\text{NaOH}, the molar mass is 23+16+1=40 g/mol23 + 16 + 1 = 40\text{ g/mol}. Multiplying 0.50 mol/dm30.50\text{ mol/dm}^3 by 40 g/mol40\text{ g/mol} yields 20.0 g/dm320.0\text{ g/dm}^3.

Step-by-Step Solution

1
Calculate the molar mass of sodium hydroxide (NaOH\text{NaOH}).
Molar mass of NaOH=23+16+1=40 g/mol\text{Molar mass of NaOH} = 23 + 16 + 1 = 40\text{ g/mol}.
Molar mass is required to convert concentration from moles per cubic decimetre to grams per cubic decimetre.
2
Convert molar solubility to mass concentration using the formula: Concentration in g/dm3=Molar concentration in mol/dm3×Molar Mass\text{Concentration in g/dm}^3 = \text{Molar concentration in mol/dm}^3 \times \text{Molar Mass}.
Concentration in g/dm3=0.50 mol/dm3×40 g/mol=20.0 g/dm3\text{Concentration in g/dm}^3 = 0.50\text{ mol/dm}^3 \times 40\text{ g/mol} = 20.0\text{ g/dm}^3.
Multiplying the amount of substance per volume by mass per mole yields mass per unit volume.

Key Concept

Conversion between molarity (mol/dm³) and mass concentration (g/dm³)
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Topics

Solubility Calculations and Concentration Determination

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