# How many more grams of KI will dissolve in 100 g of water at 40 °C than at 20°C?

##### 1 Answer
Mar 1, 2017

Here;s what I got.

#### Explanation:

Your tool of choice here will be the solubility graph for potassium iodide, $\text{KI}$, which looks like this

Now, this solubility graph expresses the solubility of potassium iodide per ${\text{100 cm}}^{3}$ of water, but you can use it as a measure of the salt's solubility per $\text{100 g}$ of water.

Notice that at ${40}^{\circ} \text{C}$, a saturated potassium iodide solution will contain about $\text{195 g}$ of dissolved potassium iodide.

At ${20}^{\circ} \text{C}$, on the other hand, a saturated potassium iodide solution will only contain about $\text{155 g}$ of dissovled potassium iodide.

These values can be found by tracing vertical lines starting from ${40}^{\circ} \text{C}$ and ${20}^{\circ} \text{C}$, respectively, until they intersect the solubility curve for potassium iodide. The values that correspond to these points represent the solubility of the salt in a saturated solution.

Therefore, you can say that a saturated solution of potassium iodide will hold $\text{40 g}$ more potassium iodide at ${40}^{\circ} \text{C}$ than at ${20}^{\circ} \text{C}$.

That is the case because

overbrace("195 g")^(color(blue)("solubility at 40"^@"C")) - overbrace("155 g")^(color(purple)("solubility at 20"^@"C")) = "40 g"