Question | Answer |
Who checks the purity and the safety of our water? | Analytic chemists |
What is qualitative analysis? | The investigation of the kind of substances present in a sample |
What is quantitative analysis? | The measuring of the amount of each substance present in a sample |
What are cations? | Positive ions |
What are anions? | Negative ions |
What are ionic compounds made of? | Cations and anions |
What does water often contain? (dissolved) | Ionic compounds |
How do analytic chemists indentify unknown ionic compounds? | By carrying out tests for each ion |
What is needed to identify a compound? | Both the anion and the cation |
What must an ion test give? | Positive results with only one type of ion |
What can be used to detect some metal cations? | A flame test |
What flame colour is calcium? | Brick red |
What flame colour is sodium? | Yellow |
What flame colour is potassium? | Lilac |
What flame colour is copper? | Green/blue |
How can you test for other cations? | By adding a few drops of sodium hydroxide solution to the unknown substance |
Why does adding a few drops of sodium hydroxide solution to an unknown substance work? | Because many metal hydroxides are insoluble, so a precipitate reaction can occur |
What is the colour of the solid formed by the precipitation of aluminium? | White (when excess sodium hydroxide is added, the precipitate redissolves to form a colourless solution) |
What is the colour of the solid formed by the precipitation of calcium? | White (when excess sodium hydroxide is added, the precipitate remains the same) |
What is the colour of the solid formed by the precipitation of copper(II)? | Pale blue |
What is the colour of the solid formed by the precipitation of iron(II)? | Green |
What is the colour of the solid formed by the precipitation of iron(III)? | Brown (rust) |
How will the name of the precipitate formed be formed? | It will be a solid hydroxide of the solution |