Aluminium salts are used to clean water entering a water works but must be removed before the water is supplied to homes. What chemical could be added to a sample of the water to check that all the aluminium has been removed?

To check if all the aluminium has been removed from the water, you could add a chemical called Eriochrome Cyanine R. This chemical is a complexometric indicator used for the detection of aluminium ions in water.

Here are the steps:

1. Take a sample of the treated water.
2. Add a few drops of Eriochrome Cyanine R to the water sample.
3. If the aluminium has been completely removed, the solution will remain clear.
4. If there is still aluminium present, the solution will turn blue.

This is because Eriochrome Cyanine R forms a blue complex with aluminium ions, making it easy to visually detect the presence of aluminium in the water.

To check if all the aluminium has been removed from the water, you can add a chemical called Eriochrome Cyanine R. This chemical is a complexometric indicator used for the detection of aluminium ions in water. Here are the steps:

1. Take a sample of the water that has been treated to remove aluminium salts.
2. Add a few drops of Eriochrome Cyanine R to the water sample.
3. If aluminium is present, the solution will turn blue. If the water remains clear, it indicates that all the aluminium has been successfully removed.

Please note that this is a qualitative test and will only indicate the presence or absence of aluminium, not the exact amount. For a quantitative analysis, more sophisticated methods like atomic absorption spectroscopy or inductively coupled plasma mass spectrometry would be needed.