NESA Chemistry Analysis of Inorganic Substances

Which pair of ions produce different colours in a flame test?

A student is presented with two clear colourless solutions. One contains Pb$^{2+}$ and the other Na$^+$ ions.

Which ion can be added to the solutions to identify the solutions?

A student attempted to determine the % w/w of sulfate in a sample of solid fertiliser. They used the procedure described below.

1. Weigh a clean, dry beaker.
2. Add fertiliser to the beaker and weigh again.
3. Add 250 mL of distilled water and stir thoroughly.
4. Add 20 mL of 0.1 mol L$^{-1}$ BaCl$_2$ solution.
5. Filter out the BaSO$_4$ precipitate, using distilled water to ensure all of the solid is transferred from the beaker to the filter paper.
6. Put the filter paper and precipitate onto a weighed watch glass and leave them to dry for 20 minutes in the sun.
7. Weigh the watch glass, the filter paper and the precipitate.
8. Calculate the % w/w.

Justify TWO changes that can be made to the procedure to ensure more accurate results.

A water sample contains at least one of the following anions at concentrations of $1.0 \text{ mol L}^{-1}$.

• bromide (Br$^-$)
• carbonate (CO$_3^{2-}$)

Outline a sequence of tests that could be performed in a school laboratory to confirm the identity of the anion or anions present. Include expected observations and TWO balanced chemical equations in your answer.

The following procedure is proposed to test for the presence of lead(II) and barium ions in water at concentrations of $0.1\text{ mol L}^{-1}$.

1. Add excess $0.1\text{ mol L}^{-1}$ sodium sulfate solution. If a precipitate is produced, then barium ions are present.
2. Filter any precipitate produced.
3. Add excess $0.1\text{ mol L}^{-1}$ sodium bromide solution to the filtrate. If a precipitate is produced, then lead(II) ions are present.

Explain why this procedure gives correct results when only barium ions are present, but not when both barium and lead(II) ions are present. Include ONE balanced chemical equation in your answer.