Question

Which of the following solutions have the same concentration?

(i) \[\ce{20 g of NaOH in 200 mL of solution}\]

(ii) \[\ce{0.5 mol of KCl in 200 mL of solution}\]

(iii) \[\ce{40 g of NaOH in 100 mL of solution}\]

(iv) \[\ce{20 g of KOH in 200 mL of solution}\]

Answer 1

(i) \[\ce{20 g of NaOH in 200 mL of solution}\]

(ii) \[\ce{0.5 mol of KCl in 200 mL of solution}\]

Explanation:

(i) The number of moles is given by the following formula,

Moles = `"Mass"/"Molar mass"`  ......(1)

So, the number of moles of \[\ce{NaOH}\] is calculated, by using equation (1) as follows,

Moles of NaOH = `(20 g)/((40 g)/(mol)` = 0.5 mol

The molarity (M) is given by the formula:

M = `n/V_((L))`

On substituting the values in the above equation:

M_NaCH = `(0.5  mol xx 1000)/(200  L)` = 2.5 mol L^–1

(ii) The molarity is given by the formula:

M = `n/V_((L))`

On substituting the values in the above equation:

M_KCl = `(0.5  mol xx 1000)/(200  L)` = 2.5 mol L^–1