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In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate - AQA - GCSE Chemistry - Question 4 - 2015 - Paper 3
Question 4
In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Hard water can be softened... show full transcript
Worked Solution & Example Answer:In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate - AQA - GCSE Chemistry - Question 4 - 2015 - Paper 3
Step 1
Ion exchange
Answer
In the ion exchange method, hard water containing calcium and magnesium ions passes through a resin column. The resin is made of sodium ions that can exchange with the calcium and magnesium ions in the hard water. As the hard water flows through the column, the calcium and magnesium ions are removed, and sodium ions replace them, resulting in softened water. This method is effective but requires periodic replenishment of the resin to maintain effectiveness.
Step 2
Adding sodium carbonate (washing soda)
Answer
In this method, sodium carbonate is added to hard water. The sodium carbonate reacts with the calcium ions present in the hard water to form calcium carbonate, which precipitates out of the solution, effectively softening the water. This method is simple and does not require special equipment, but the resulting calcium carbonate can create residues, and the process can also lead to the continuous removal of calcium ions as it precipitates.
Step 3
Compare the advantages
Answer
The ion exchange method offers continuous softening and is efficient in removing hardness, however, it requires maintenance of the resin. In contrast, adding sodium carbonate is straightforward and easy to perform without special equipment, but can lead to residue build-up and might not be as efficient for ongoing softening. Therefore, the choice of method can depend on the specific needs of the water treatment situation.