Science 8th grade
UNIT 8: Mixtures 8.6 Solubility
Science 8th grade
UNIT 8: Mixtures 8.6 Solubility
Solutions, solvents and solutes
A solution is made when a solute is dissolved in a solvent. A concentrated solution has more particles of the solute dissolved in it than a dilute solution.
A solid that dissolves in a solvent such as water is said to be soluble. Sodium chloride (common salt) and sugar are soluble.
A solid that will not dissolve in water is insoluble. Iron filings are insoluble.
If you keep on adding a soluble solid to a beaker of water, there comes a point when no more of the solid will dissolve. You have made a saturated solution.
Some soluble substances are more soluble than others. If you have $100cm$ of water, you would be able to dissolve a lot of sodium chloride in it, but only a tiny bit of lead chloride, Sodium chloride has a greater solubility than lead chloride.
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Activity 8.6 (Solubility in water)
SE: In this activity you will use the various solutes provided and investigate their solubility in water. You will use water at room temperature.
1) Place a measured volume of water in a number of test tubes. Use a different test tube for cach of the solutes.
2) Add the first solute to the water. Count how many spatulas you add until no more will dissolve.
3) Repeat for the other solutes.
4) Record your results in a table
Questions
${A_1}$: Which was the most soluble of the solutes you used?
${A_2}$: Which was the least soluble of the solutes you used?
${A_3}$: In this investigation you used spatulas as a measure of the quantity of solute added. Suggest another way of measuring the solute used which would improve the accuracy of the results.
Solubility
To compare the solubility of different solutes you must measure how much of cach solute will dissolve in $100g$ of the solvent.
| Solubility / grams of solute in $100g$ of water at ${20^ \circ }C$ | Solute |
| 36 | sodium chloride |
| 32 | copper sulfate |
| 74 | calcium chloride |
| 7 | potassium chlorate |
| 1 | lead chloride |
Questions
1) What is a saturated solution?
2) How much potassium chlorate would dissolve in $200g$ water at ${20^ \circ }C$?
SE: 3) Use the data in the table to draw a bar chart to show the solubility of the various solutes in water at ${20^ \circ }C$.
Temperature and solubility
Most solutes will dissolve more quickly and easily in hot water than in cold water.
You can also dissolve a greater mass of the solute in hot water than in the same volume of cold water. In other words, as temperature increases, the solubility of most solutes also increases.
For example, if you have $100g$ of water at ${20^ \circ }C$, you can dissolve $204g$ of sugar in it. If you hear the water to ${80^ \circ }C$, you can dissolve $362g$ of sugar in it.
Questions
4) How much sugar can be dissolved in $250g$ of water at ${20^ \circ }C$?
5) How much more sugar can be dissolved if the $250g$ of water is heated to ${80^ \circ }C$?
Water is not the only solvent. Some substances that are insoluble in water will dissolve in other solvents. Some types of ink are soluble in alcohol but not water.