What are materials made of? 2. When materials mix
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Solubility
 We compare how well solutes dissolve in solvents by measuring their solubility. The solubility of a solute is the maximum mass of the solute that you can dissolve in a specified mass of the solvent. For example, the solubility of salt in water is about 3 grams per 10 grams of water.
 Picture 2.12 When you heat water, small bubbles form as the gases come out of solution.

 How does temperature affect solubility? You can usually dissolve more solute in the same amount of solvent if you warm it up. This is because the solubility of most solids increases with temperature. This means that if you cool a solution down, less solute will dissolve in it. Some of the solute can no longer remain dissolved and it appears as solid crystals.
 What about gases? Temperature has the opposite effect on the solubility of gases. If you warm up a solution of a gas, it becomes less soluble. As the solution gets hotter you can see bubbles of gas appear. These were dissolved when the solution was cooler and now they are coming out of solution.
 Bubbles in the water You can see this when you heat water in a pan. Bubbles of air appear as the water warms up. The air was dissolved in the water when it was cold. But now that the water is hot, it can no longer stay in solution. So it appears as bubbles. Try not to confuse this with the bubbles you see when the water eventually boils. These are bubbles of steam formed as the liquid water changes into a gas.
 Question 13 Pour yourself a glass of water from the tap. It will have air dissolved in it. Stand the glass of water on a warm window sill for a while. a) What happens? b) Explain why this happens.