Chemistry · May / June 2020 · Paper 12 · Question 4

The diagram shows two experiments. [Experiment 1: Al³⁺(aq) — no precipitate; add a few drops of NaOH(aq) → precipitate formed; add an excess of NaOH(aq) → ?] [Experiment 2: Cu²⁺(aq) — no precipitate; add a few drops of NaOH(aq) → precipitate formed; add an excess of NaOH(aq) → ?] What are the results of adding an excess of NaOH(aq) in each experiment? key ✓ = precipitate remains ✗ = precipitate dissolves

1. Aexperiment 1: ✓ ; experiment 2: ✓
2. Bexperiment 1: ✓ ; experiment 2: ✗
3. Cexperiment 1: ✗ ; experiment 2: ✓
4. Dexperiment 1: ✗ ; experiment 2: ✗

As printed in the paper