The amount of a substance that will dissolve in a solvent is affected by the temperature of the solvent. We can see the effect of temperature on the solubility of solutes by looking at graphs which we call solubility curves. A solubility curve shows the amount of a solute which dissolves to produce a saturated solution at any given temperature.
We can use solubility curves to predict how much solute will form when we cool a hot solution down.
There are 2 main factors which affect the solubility of gases - temperature and pressure. Gases behave in the opposite way to solids when they dissolve in water. As the temperature increases, the amount of gas that will dissolve in a certain volume of water decreases when we keep the pressure constant. On the other hand, if we keep the temperature constant, the solubility of a gas increases as we increase the pressure.
Solubility Curves 2
There are lots of examples of the way that solubility affects our lives every day. In the kitchen we often need to dissolve solids like sugar in water. This is made easier by heating the water to increase the solubility of the solid.
Outside our homes, the artificial fertilisers that we put on the soil are very soluble in water. They dissolve in rainwater and can contaminate rivers, lakes and reservoirs. The nitrate ions in these fertilisers can be very bad for babies and some adults. This means that nitrate levels in drinking water must be carefully monitered by the water companies who supply water to our homes and schools.
Oxygen dissolved in water is essential to keep animals living in water alive. When we pump hot water from the cooling towers of power stations into rivers it contains no chemical pollution.
However, the warm water from the power station increases the temperature of the water in the river. This reduces the amount of oxygen dissolved in it. We call this thermal pollution. It can be very bad for wildlife living in the river, especially fish.
Solubility Curves 3
Another example of the importance of dissolved gases is the fizzy drinks that many of us enjoy. The carbonated water we use to make them is produced by dissolving Carbon Dioxide in water at high pressures before bottling or canning the drink. When we open the can or bottle and release the pressure, the gas comes out of the solution and provides us with the fizz.
Lemonade, Cola and other sparkling drinks that have been allowed to stand a while are not very fizzy. Thats because the have warmed up and a lot of the Carbon Dioxide has come out of the solution.