Solubility curves are graphs that show how much solute can dissolve in 100 g of water. Usually, many substances are shown on a single solubility curve. On the solubility curve above, nine different substances are shown.
On all solubility curves, temperature is on the x-axis, because it is the independent variable. It is the variable that we can control. The dependent variable goes on the y-axis. This is the variable that responds to the independent variable. Solubility is on the y-axis. Note that the solubility is measured as the grams of solute in 100 g of water.
Notice on the solubility curve that for most substances, the solubility increases as the temperature increases. For which substance is this not true?
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Solubility curves tell us at what point a solution is saturated, unsaturated, or supersaturated. Any point that falls on the line or curve for a solute would be a point of saturation. Any point that falls below the line or curve for a solute would represent an unsaturated solution. Any point that falls above the line or curve for a solute would represent a supersaturated solution.
For the questions below, an amount of solute is given and the temperature is stated. If all of the solute could be dissolved in 100 g of water at the given temperature, would the resulting solution be unsaturated, saturated, or supersaturated? Use the solubility curve:
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1. 60 g KCL at 70 °C
2. 10 g KCLO3 at 60 °C
3. 80 g NaNO3 at 10 °C
4. 70 g CaCl2 at 20 °C
For the questions below, a solute and temperature are given. Tell approximately how many grams of each solute must be added to 100 g of water to form a saturated solution at the given temperature.
5. Pb(NO3)2 at 10 °C
~ 46 g
6. Ce2(SO4)3 at 50 °C
7. NaCl at 20 °C
8. K2Cr2O7 at 50 °C
Which solution is more concentrated?
9. At 10 °C: a saturated solution of KNO3 or a saturated solution of CaCl2.
a saturated solution of CaCl2
10. At 50 °C: a saturated solution of KNO3 or an unsaturated solution of NaNO3 consisting of 90 g of the solute dissolved in 100 g of water.
Answer</summaryan unsaturated solution of NaNO3 consisting of 90 g of the solute dissolved in 100 g of water
11. If 115 g KNO3 are added to 100 g of water at 35 °C, how many grams do not dissolve?
115 g are added. From the graph, ~54 g of KNO3 will dissolve in 100 g of water at 35 degree C
12. What mass of KCl would be needed to form a saturated solution if the KCl was dissolved in 200 g of water at 80 °C?
~52 g of KCl will dissolve in 100 g of water at 80 degree C
To determine how much will dissolve in 200 g of water at 80 degree C, multiply that by 2, or set up a ration and cross multiply.
52 g KCl/100 g H2O = x g KCl/200 g H2O = 104 g KCl