Solutions

Aim: To understand the concept of solutions At the end of this section you will know: Terms, solvent, solute, solution + examples (2) Difference between melting and dissolving Terms suspension, dilute, concentrated Explain concentration with particle theory. Saturated solution, solubility with temp.+e.g.(2) How solubility is measured. How to graph solubility against temperature (solubility curve). Must be able to read graph. Crystallisation, different type of solutes/ solvents (3) Dangers of other solvents (3)

Keywords

Solutions  Clear mixtures in which parts are too small to be seen and do not settle.  Consist of 2 parts:  Solvent: does the dissolving e.g water, nail varnish remover.  Solute: is dissolved e.g. sugar, nail varnish  Solution = mixture of solute and solvent

Examples of Solutions Minerals are solutions of carbon dioxide, sugar, and flavorings dissolved in water. An alloy is a solid solution of metals.

What increases how much dissolves?  Crushing the solute  Heating the solvent, if you are dissolving a solid in a liquid  Stirring the solution

What is a suspension?  When a finely divided solid is scattered throughout a liquid you have a suspension.  Any liquid you have to shake before use is a suspension. e.g milk of magnesia, milk, mud and water.

Concentrated Solutions Concentrated solutions have more solute and less solvent. e.g Orange juice or blackcurrent juice you buy in the supermarket to dilute for drinking.

Dilute Solutions 1)`When a solution has little solute and alot of solvent it is called a dilute solution. 2)In the large beaker there are very few solute molecules so it is a dilute solution 3)So how can a dilute solution be made more concentrated?

Dilute Solutions ANSWER 1)Add more solute. 2)Evaporate some of the solvent. 3)In the diagram the copper sulphate solution is made more concentrated by adding more copper sulphate.

Saturated, unsaturated, or supersaturated?  solutions hold the maximum amount of solute at a given temperature  solutions are not holding as much as possible at that temperature  solutions are holding more than they should be able to at the given temperature.

This solution is saturated. It is holding all it can, and we can see some undisolved solute.

Solubility and Solubility Curves From copper sulfate experiment you will have noticed that the copper sulfate dissolved easier in hot water than cold water. It is clear that the higher the temperature the more substance that dissolves. Solubility = the mass of a substance in grams that will dissolve in 100g of solvent at a fixed temperature. Solubility is different for different substances at the same temperature.

Solubility Curve Looking at the curve for Potassium Nitrate you can see that as the temperature rises the solubility rises rapidly. For Sodium Chloride the rise in solubility with temperature is much slower.

Using Solubility Curves Use the results in the table opposite to draw a solubility curve graph for Copper Sulfate. Put temperatute on the horizontal axes Put solubility of copper sulfate / 100g of water on the vertical axes. Temp/ o CCuSO 4 /100g water

Solubility Curve Graph

Graph Questions How much Copper Sulfate (CuSO 4 ) dissolves at 65 o C If the solution is cooled from 80 o C to 20 o C how much copper sulfate is put out solution to form crystals? ANSWERS At 65 o C 43g of copper sulfate will dissolve in 100g of water. At 80 o C 56g of copper sulfate dissolves. At 20 o C only 20g of copper sulfate dissolves. So if the solution is cooled 56 g – 20 g will come out of solution that is 36 g of crystals.

Solubility Curve Graph 56g At 80 o C 20g at 20 o C

Crystallisation Crystallisation is the formation of crystals when a hot saturated solution is cooled or when solvent is evaporated from the solution. Copper Sulphate crystals

Other types of solutions Solutions are not always a solid solute in a liquid solvent e.g. Fizzy drinks contain carbon dioxide (gas) dissolved in water. Whiskey and other alcoholic drinks contain alcohol (liquid) dissolved in water. Marshmallows contain air (gas) dissolved in sugar pastes (solid) Other solvents Alcohol, chloroform, white spirit are solvents.

Dangers of other solvents Solvents used in paint are flammable. Solvents used in glue are extremely poisonous and can cause damage to the brain, liver and other parts of the body.