Question

How many grams of solid KCl would be obtained if 100mL of a solution with a 0.5M solution of KCl was evaporated to dryness?

I know that the answer is 3.73 grams. But I have no idea on how to work this out.

Answer 1

Answer on Question #43524 - Chemistry - Inorganic Chemistry

Question:

How many grams of solid KCl would be obtained if 100 mL of a solution with a 0.5 M solution of KCl was evaporated to dryness?

Answer:

$$\text{molarity} = \frac{\text{moles of solute}}{\text{liter of solution}}$$

From this equation we calculate moles of solute of KCl in 100 mL of 0.50 M.

$$\text{moles of solute} = \text{molarity} \times \text{liter of solution} = 0.5 \mathrm{M} \times 0.1 \mathrm{L} = 0.05 \text{ moles}$$

Now we calculate mass of 0.05 moles of KCl which left after evaporation of 100 mL of a solution with a 0.5 M of KCl.

$$\theta = \frac{m}{M}$$

where $\theta$ – is number of moles of KCl, $m$ – is mass of KCl, $M$ – is molecular mass of KCl.

$$M(KCl) = 39.0983 + 35.453 = 74.5513 \approx 74.55 \frac{g}{mole}$$

So mass of KCl is:

$$m = \frac{\theta \times M}{mole \times 74.55} \frac{g}{mole} = 3.7275 \frac{g}{g} = 3.73 \frac{g}{g}$$

Answer: mass of KCl is 3.73 g

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