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Comparing the solubility's of copper sulphate, sodium chloride and potassium nitrate.

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Introduction

Comparing the solubility's of copper sulphate, sodium chloride and potassium nitrate Comparing the solubility's of copper sulphate, sodium chloride and potassium nitrate Background Information Molecular solids (sugar) and ionic solids (salts) both dissolve in water. However, they both dissolve in different ways. The intermolecular forces holding molecules of sugar together are relatively weak so when sugar is placed in water these bonds are broken and individual C12H22O11 molecules are released into solution. It takes energy to break bonds between C12H22O11 molecules and it also takes energy to break the hydrogen bonds in water. These hydrogen bonds have to be disrupted in order to insert a sugar molecule into the substance. The energy needed for this is produced by the forming of bonds between slightly polar sucrose molecules and polar water molecules. This process works so well between sugar and water that up to 800g of sugar can dissolve in 1 litre of water. The positive and negative ions in ionic solids (or salts) are held together by the strong force of attraction between particles with opposite charges. When a salt dissolves in water the ions are released and become associated with the polar solvent molecules. ...read more.

Middle

3. Potassium Nitrate - Colourless crystals. May ignite combustible materials. (KNO3) May evolve toxic fumes. Prediction Below is information from a data booklet: Copper Sulphate - 1.39 � 10� moles dissolve in 100g of water. Sodium Chloride - 6.15 � 10� moles dissolve in 100g of water. Potassium Nitrate - 3.75 � 10� moles dissolve in 100g of water. Working out the quantities that will dissolve in grams shows that according to this information 29.12g of copper sulphate will dissolve, 35.98g of sodium chloride will dissolve and 37.88g of potassium nitrate will dissolve in 100g of water. I carried out some preliminary tests that showed that more of the salts dissolved as we increased the temperature. Obviously these tests could be accurate, as I did not have time to plan them carefully. However, they do show that as the temperature was increased, the solubility also increased. Having looked at the information given by the data booklet and my own preliminary work, I think that as the temperature increases the solubility of all the salts will increase. Equipment 3 boiling tubes, a burette, a thermometer, ceramic mat, Bunsen burner Method Weigh out about 10g of copper sulphate and record its mass. ...read more.

Conclusion

Again take a new boiling tube and place the potassium nitrate in it. Repeat the method above taking readings from the same volumes of distilled water. Now repeat the whole experiment another two times and average the readings you get. Ignore any readings which are completely different to the other two as these will probably be due to an error. Now work out the solubility of each salt at different temperatures per 100g of water. For instance if 10g of copper sulphate dissolves in 20cm� of water then the solubility of copper sulphate at the temperature you recorded will be 50g per 100g of water. Once you have worked out all the solubility's at different temperatures you can plot a solubility curve graph. Put solubility per 100g water on the vertical axis and temperature on the horizontal axis. Plot the points for each salt and join them with a line of best fit. Now you should have three separate solubility curves on the same graph. Sources of Error Human error -it is very hard to tell the exact temperature at which crystals come out of the solution, so mistakes here are probable. To reduce the chance of error use the same thermometer and the same person taking the readings. ...read more.

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