a) iii) To another portion of the filtrate, add 2 drops of barium nitrate followed by 1 cm^3 of 2M nitric acid.
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Here are the observations and inferences for the tests on solid M:
a) iii) To another portion of the filtrate, add 2 drops of barium nitrate followed by $\text{1 cm}^{3}$ of 2M nitric acid.
| Observations | Inferences |
| :----------------------------------------- | :---------------------------------------------------------------------- |
| A white precipitate forms. | $\boxed{\text{Sulfate ions } (\text{SO}_{4}^{2-}) \text{ are present.}}$ |
b) Dry the residue using a filter paper.
i) Using a clean spatula, transfer about half of the residue in a dry test tube, heat the residue strongly and test the gas produced using moist blue and red litmus papers.
| Observations | Inferences |
| :------------------------------------------------------------------------ | :---------------------------------------------------------------------- |
| A colorless gas is produced. The gas turns moist blue litmus paper red. Moist red litmus paper remains red. | $\boxed{\text{An acidic gas is produced, likely carbon dioxide } (\text{CO}_{2}). \text{ Carbonate is present.}}$ |
ii) Place the remaining residue in a dry test tube. Add 2M nitric acid until all the solid dissolves. Retain the mixture for test (iii) below.
| Observations | Inferences |
| :------------------------------------------------------------------------ | :---------------------------------------------------------------------- |
| The white residue dissolves with effervescence to form a colorless solution. | $\boxed{\text{The residue is a carbonate or sulfite.}}$ |
