A student was trying to identify the ions present in a dilute aqueous solution - HSC - SSCE Chemistry - Question 30 - 2021 - Paper 1

The procedure involves several tests aimed at identifying the ions. However, its effectiveness is debatable due to certain limitations:

Sodium Chloride Test

The first test with aqueous sodium chloride shows no visible reaction, indicating that either the cation is not sodium, or the tested anion does not form a precipitate with the chloride ions. This test does not provide substantial information about the nature of the ions present.

Silver Nitrate Test

In the second test, adding silver nitrate produced a brown precipitate, which is indicative of the presence of silver ions. However, the precipitate dissolving upon the addition of dilute hydrochloric acid suggests that the anion could be hydroxide or acetate. This test is appropriate for analyzing the anions, though it is unable to differentiate between hydroxide and acetate accurately. More specific tests would be needed to ascertain which ion is present conclusively.

Sodium Sulfate Test

The final test with concentrated aqueous sodium sulfate yielding a white precipitate is useful in indicating the presence of barium or calcium. However, since both barium and calcium hydroxides form white precipitates, this test alone would not help in distinguishing between the two cations.

Conclusion

Overall, the procedure is insufficient for definitively identifying all ions in the solution. While some ions are suggested by the color of precipitates, the overlap between ions (like barium and calcium, and the ambiguity between hydroxide and acetate) indicates that further specific tests are necessary. A flame test could have been used to conclusively identify the presence of certain cations, providing a more reliable method of identification.