What is “hard water”? Deionised water The higher the dissolved mineral content of water, the “harder” it is. Common mineral ions found in water include calcium 1 (Ca2+) and magnesium (Mg2+). Mineral ions dissolve in rainwater as it runs over rocks because it is slightly acidic. This means that the hardness of water varies from place to place, 2 depending on the kinds of rocks that are present: in Wales, for example, the water is very very soft, whilst in the East Midlands Repeat 1 it is extremely hard. You can see how hard or soft a sample of water is because the mineral ions react with soap – forming Repeat 2 scum on the surface of the water – and so delaying the formation of a lather. Water hardness can be temporary – where dissolved hydrogen Why did you test and compare your findings to a sample of carbonates are precipitated as carbonates on boiling – or permanent – deionised water? where no precipitation happens after boiling and sulphates or chlorides are present. Having read the paragraph above, write out the conclusions you Why is it important to repeat the experiment? have drawn from the experiment above. Conclusions:
Deionised water 1 2 Repeat 1 Repeat 2 Why did you test and compare your findings to a sample of deionised water? Why is it important to repeat the experiment? What is “hard water”? The higher the dissolved mineral content of water, the “harder” it is. Common mineral ions found in water include calcium (Ca2+) and magnesium (Mg2+). Mineral ions dissolve in rainwater as it runs over rocks because it is slightly acidic. This means that the hardness of water varies from place to place, depending on the kinds of rocks that are present: in Wales, for example, the water is very very soft, whilst in the East Midlands it is extremely hard. You can see how hard or soft a sample of water is because the mineral ions react with soap – forming scum on the surface of the water – and so delaying the formation of a lather. Water hardness can be temporary – where dissolved hydrogen carbonates are precipitated as carbonates on boiling – or permanent – where no precipitation happens after boiling and sulphates or chlorides are present. Having read the paragraph above, write out the conclusions you have drawn from the experiment above. Conclusions: