After filtering, how are traces of soluble salt removed from the precipitate?

• A. Wash the filter paper with distilled water
• B. Rinse with strong acid
• C. Dissolve the precipitate and re-precipitate
• D. Dry it immediately without washing

Answer: (A)

The key idea is that washing with water takes advantage of solubility. Any soluble salt impurities will dissolve in the water, and as you rinse, these dissolved substances are carried away through the filter, leaving the insoluble precipitate behind on the filter paper. Using distilled water is important because it doesn’t introduce extra ions that could contaminate the purified solid. If you used something acidic, the precipitate might dissolve or react; drying without washing would leave soluble impurities on the solid, and dissolving and re-precipitating is a more involved purification step not needed here.