JAMB - Chemistry (2012 - No. 16)
Potassium trioxochlorate (V)has a solubility of 1.5 mol dm -3 at 45 oC.On cooling this solution to a temperature of 20 oC, the solubility was found to be 0.5 mol dm -3. What mass of KCIO 3 was crystalized out?
[K = 39, Cl = 35.5 O =16]
[K = 39, Cl = 35.5 O =16]
1.00g
10.00g
12.25g
122.50g
Explanation
Given:
Solubility of KClO\(_3\) @ 45\(^0\)C = 1.5 moldm\(^{-3}\)
Solubility of KClO\(_3\) @ 20\(^0\)C = 0.5 moldm\(^{-3}\)
Difference in Solubility = 1.5 moldm\(^{-3}\) - 0.5 moldm\(^{-3}\) = 1.0 moldm\(^{-3}\)
Recall that Solubility = \(\frac{mass}{Molar mass}\times 1 dm^3\)
Also, Molar mass of KClO\(_3\) = 39 + 35.5 + (16 x 3) = 122.5g
Solubility = \(\frac{mass}{Molar mass}\times 1 dm^3\)
1.0 = \(\frac{mass}{122.5}\times 1 dm^3\)
Mass = 1.0 x 122.5 = 122.5g
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