Common Ion Effect

The question pertains to the coagulating power of ions, which is a concept in colloidal chemistry. The coagulating power of an ion is important in determining how it can cause the aggregation of colloidal particles, leading to the settling or precipitation of the colloid.

Explanation:

1. According to the Hardy-Schulze rule, the coagulating power of an ion is directly related to both the magnitude and the sign of the charge on the ion.
2. The rule states that ions with higher charges are more effective at coagulating colloids than ions with lower charges. This is because higher charge causes a greater neutralization of the opposite charge on the colloidal particles, leading to aggregation.
3. The sign of the charge is also crucial. The ion must have a charge sign opposite to that of the colloidal particles. For example, positively charged ions are needed to coagulate colloids made up of negatively charged particles, and vice versa.

Analysis of Options:

• Option 1: The magnitude of the charge on the ion alone – While magnitude is important, it is not the only factor as the sign of the charge is also crucial.
• Option 2: Both magnitude and sign of the charge on the ion – Correct. Both factors influence the coagulating power, as explained by the Hardy-Schulze rule.
• Option 3: Size of the ion alone – Irrelevant in this context as coagulation depends more on charge factors.
• Option 4: The sign of charge on the ion alone – The sign alone is insufficient without considering the magnitude.

Conclusion: The correct answer is that the coagulating power of an ion depends on both the magnitude and the sign of the charge on the ion.