Chapter U1.20, Problem 2E

Interpretation Introduction

Interpretation:

The role of zero charge rule to determine the chemical formula of an ionic compound needs to be explained.

Concept introduction:

Rule of zero charge states that a compound is neutral or there is no charge on it. It means total positive charges of cation must be counter balanced by total charge on anion in a compound.

Answer to Problem 2E

Number of cations and anions of an ionic compound should be such that total charge of the compound is zero.

Explanation of Solution

This can be explained by taking example of magnesium which has valency 2 and form magnesium cation (Mg + 2) by removal of 2 electrons.

Chlorine has 7 valence electrons and it produces chloride ion (Cl^-) by accepting 1 electron. So to make the neutral compound, one magnesium and two chlorine must combine to produce magnesium chloride (MgCl₂).

Similarly, potassium can gain 1 electron and chlorine can lose 1 electron. So make a neutral compound neutral, one potassium ion needs one chloride ion. Thus, formula is KCl.

Conclusion

Thus, the correct chemical formula can be predicted from the zero charge rule.