Playing with Solubility 2

Chemistry Level 2

If a 150 g $\ce{KNO3}$ solution contains 68 g of $\ce{KNO3}$ , what is the amount (in grams) of $\ce{KNO3}$ crystal that will separate out if I cool down the solution to $20^\circ\text{C}$ ?

The solubility of $\ce{KNO3}$ is $30\text{ g}/100\text{ g}$ water at $20^\circ\text{C}$ .

The answer is 43.4.

1 solution

Chew-Seong Cheong
Feb 4, 2016

If the $\ce{150 g \space KNO3}$ solution has $\ce{68 g}$ of $\ce{KNO3}$ then there is $150 - 68 = \ce{82 g}$ of water.

At $20^\circ C$ the solubility of $\ce{KNO3}$ is $\dfrac{\ce{30 g}}{\ce{100 g}}$ , therefore, $\ce{82 g}$ of water can dissolve $\dfrac{30}{100} \times 82 = 24.6 \text{ g}$ of $\ce{KNO3}$ .

Therefore, the amount of $\ce{KNO3}$ crystals that separates out is $68 - 24.6 = \boxed{43.4} \text{ g}$ .

Playing with Solubility 2

The answer is 43.4.

1 solution

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