Read the passage carefully and answer the Questions.
A homogeneous mixture of two or more than two components has uniform composition and properties. The binary solutions have two components, which may be solid, liquid or gas. The resultant solution has a larger amount of solvent and a smaller amount of solute. The amount of solute in a given amount of solvent decides the concentration of the resulting solution. The concentration can be expressed in various ways, like molarity, molality, normality and mole fraction.
Molarity of a solution containing 8 grams NaOH in one liter of water is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 0.20 mol/L
Molarity (M) is the number of moles of solute per litre of solution:
\( \displaystyle M = \frac{\text{moles of solute}}{\text{volume of solution in L}} \)
First the moles of NaOH, with molar mass \( 23 + 16 + 1 = 40\,\mathrm{g\,mol^{-1}} \):
\( \displaystyle n = \frac{8\,\mathrm{g}}{40\,\mathrm{g\,mol^{-1}}} = 0.2\,\mathrm{mol} \)
In a dilute solution like this, dissolving 8 g of NaOH hardly changes the volume, so the volume of the solution is taken as 1 L:
\( \displaystyle M = \frac{0.2\,\mathrm{mol}}{1\,\mathrm{L}} = 0.20\,\mathrm{mol\,L^{-1}} \)
So the molarity is 0.20 mol/L.