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Which ions cause hardness in water?

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Investigation Which ions cause hardness in water? Aim: I want to find out what ions cause hardness in water and the reasons as to why certain ions have an effect and others don't. Background information: Calcium hydrogen carbonate is the main cause of hard water. It forms when rain falls on rocks of limestone and chalk. These are made of calcium carbonate, which is not soluble in water. But rainwater contains carbon dioxide dissolved from the air, which makes it acidic. So it reacts with the rocks to form calcium hydrogen carbonate which is soluble and ends up in our taps. This reaction is: H20(l) + C02(g) + CaC03 - Ca(HCO3)2(aq) (Information taken from Complete Chemistry Book-Oxford University.) ...read more.


I also know that soap can be used to soften hard water, the chemical equation for this is: CaSO4+ 2C17H35COONa=Ca (C17H35COO)2+Na2SO4 (Calcium Sulphate+ Sodium Stearate= Calcium Stearate+ Sodium Sulphate) I think that the ions most likely to cause hardness are probably the 2+ ions because the cations seem to be the only thing that is having an affect on the situation. Method: The apparatus I will need to use is minimum, a test-tube, pipette and a measuring cylinder. I have to measure 6 ml of the chosen compound e.g. iron sulphate, to do this I will need to use a pipette to make sure that the measurements are very accurate. I need to measure 2 ml of Sodium Stearate (soap solution), which is to be added. ...read more.


Compounds with a cation charge of one were only present in soft water; anions were present in both hard and soft water, which by observation means that they have no affect. So by the evidence claimed only compounds with a cation charge of two produce scum. Evaluation: The results I obtained were all correct; there were no signs of anomalous results. As there were only two possible outcomes this made it easier to get the right result. I did each experiment twice to make sure that nothing could have gone wrong, to improve the experiment I could have used equipment that can measure the amount of scum or lather produced; also I could look into the effect of temporary hard water. ...read more.

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