Question

Identify the spectator ions in the following molecular equation.
KBr(aq) + AgNO3(aq) → AgBr(s) + KNO3(aq)
I'm not sure what the rules are for assigning oxidation numbers.

Answer 1

This problem doesn't require you to know anything about oxidation numbers. It is a simple double displacement reaction. As you probably know, when ionic compounds are dissolved in water (denoted by "aq"), many dissociate into their component ions. Sometimes, as in this case, the ions will react with each other to form a product that is not soluble in water and so will form a solid precipitate instead (denoted by "s").

In your case, the solid precipitate is AgBr. However, KNO3 is still aqueous, meaning it remains dissolved. The ions effectively remain dissociated, even though we write them together as a single compound. Because they are not involved in a reaction, we call them spectator ions. Therefore, the spectator ions are K+ (aq) and NO3- (aq).

Answer 2

thank you!