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Which Ions Cause Hardness in Water?

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Chemistry Investigation Which Ions Cause Hardness in Water? Objective of Investigation The objective of this investigation is to find out which ions out of the following cause hardness in water: Na+ Cl- Ca2+ Mg2+ K+ NO3- SO42- Fe2+ Prediction Due to the fact that I have already learnt that hard water is caused by calcium ions and magnesium ions, such as in the case of temporary hard water being caused by calcium hydrogen carbonate, I am certain that the subsequent experiment will echo those facts. It would also be logical to assume that the ions that cause hard water would be linked, or be similar in some way. As they would obviously share the same properties in causing hard water, one would assume that they would share other properties. Apart from causing hard water, calcium and magnesium also share other properties. They are in the same group in the periodic table, and thus their properties are in fact very similar. As they are in the same group, then their ions will both have the same charge, in this case, 2+. ...read more.


Also, from work done on another method of softening hard water, ion exchange, I am certain that sodium ions do not cause hard water. On a basic level, ion exchange works by simply exchanging the ions that cause hard water (Calcium for example) for Sodium ions. As Sodium ions do not cause hard water, scum would no longer be formed if soap was added. As Sodium is not a cause of hard water, and it is a positive ion with a 1+ charge, I would say that all other ions with a 1+ charge are not causes of hard water. Therefore I have so far predicted that ions which cause hard water will have a 2+ charge, and those ions with a 1+ charge are not causes of hard water. That means that I have predicted the effect that 5 of the ions I will be testing will have on the hardness of water. The 3 ions that I have not accounted for are all negatively charged. This means that they will not fit into the equation of the reaction between soap and the hard water causing salt. ...read more.


Therefore in scum there must be 1 hard water causing ion to 2 stearate ions. Therefore it is obvious that hard water is not caused by anions, of any strength of charge, as they just simply won't form an ionic bond with another anion, in this case stearate. Thus to summarise my prediction, I predict that out of the ions I was assigned to test, the following will cause hard water: Mg2+ Ca2+ Fe2+ Basically, all cations with a charge of 2. Plan As I can obviously not test each ion for the property of causing hard water individually, ionic compounds consisting of two of the said ions shall have to be used. Obviously as each compound will be ionic, one ion will be a cation, and one will be an anion. As the method that is being used to determine whether or not an ion causes hard water is just simply whether or not soap will lather when added to a sample of a solution of an ionic compound, if the soap didn't lather, and formed a scum, it would be hard to determine which ion was the cause of hard water without prior knowledge. However, ...read more.

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