The Na2CO3 used in step 5 of Figure 3 is necessary to:

• A. increase the solubility of metal salts in water
• B. precipitate metal ions by forming insoluble carbonates
• C. neutralize excess acid in the solution
• D. act as an oxidizing agent to convert metal ions to higher oxidation states

Answer: (B)

Verified step by step guidance

1. Understand the role of \( \text{Na}_2\text{CO}_3 \) (sodium carbonate) in aqueous solutions, particularly in reactions involving metal ions.
2. Recall that sodium carbonate can react with metal ions to form metal carbonates, many of which are insoluble in water and precipitate out of solution.
3. Recognize that increasing solubility of metal salts is not the function of \( \text{Na}_2\text{CO}_3 \); instead, it tends to remove metal ions from solution by precipitation.
4. Consider the possibility of neutralizing excess acid: while \( \text{Na}_2\text{CO}_3 \) is a base and can neutralize acids, in this context its primary role is related to metal ion precipitation rather than acid neutralization.
5. Note that \( \text{Na}_2\text{CO}_3 \) is not an oxidizing agent, so it does not change the oxidation state of metal ions; its main function is to precipitate metal ions by forming insoluble carbonates.