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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) \[\ce{20 g of KOH in 200 mL of solution}\]
Solution
(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:
MNaCH = `(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:
MKCl = `(0.5 mol xx 1000)/(200 L)` = 2.5 mol L–1
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