Question

6a. make a claim as to why sodium carbonate caused this change.

Explanation:

Sodium carbonate is a base. In chemical reactions, it can react with acids to neutralize them, or with certain metal - ions to form precipitates. Depending on the context of the "change" (e.g., a change in pH, formation of a solid), its basic nature and reactivity with other substances in the system can cause the observed change.

Answer:

Sodium carbonate is a base and can react with acids or certain metal - ions, causing the observed change depending on the reaction system.