(b) The labels on a bottle of hydrochloric acid and a bottle of sodium hydroxide
have fallen off. Describe two tests that can be carried out in a laboratory
to differentiate the contents of the bottles. For each test, describe how it is
carried out and state what would be observed for the acid and the alkali.

test 1:
test 2:

Explanation:

Flame tests for metal ions

There are several different tests to detect and identify the ions in compounds. It is important that the test for any ion is unique.

Flame tests

Different metal ions produce different flame colours when they are heated strongly. This is the basis of flame tests. To carry out a flame test:

dip a clean wire loop into a solid sample of the compound being tested

put the loop into the edge of the blue flame from a Bunsen burner

observe and record the flame colour produced

A sample is held in a Bunsen burner flame and burns red.

Carrying out a flame test

The table shows the flame test colours for six common metal ions.

Lithium, Li+Red

Sodium, Na+Yellow

Potassium, K+Lilac

Calcium, Ca2+Orange-red

Barium, Ba2+Green

Copper, Cu2+Blue-green

Worked example

A sample of an ionic compound produces an orange-red flame test colour. Identify the metal ion present.

The metal ion is calcium, Ca2+.

Each metal ion produces a different flame test colour.

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

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