Video Transcript
Select the spectator ions in the following reaction: two AgNO3 aqueous plus (NH4)2CrO4 aqueous react to produce Ag2CrO4 solid plus two NH4NO3 aqueous. (A) Ag+ and CrO4 2−, (B) Ag+ and NH4+, (C) NO3− and NH4+, (D) NO3− and CrO4 2−, or (E) NO3− and Ag+.
To answer this question, we need to determine which ions are the spectator ions in the given reaction. Spectator ions are ions that exist as a reactant and product in an ionic equation but do not take part in the chemical reaction. To determine which ions are spectator ions, let’s take a closer look at the reactants and products of this equation.
The reactants, silver nitrate and ammonium chromate, are both ionic compounds. In addition, both substances are aqueous or dissolved in water. When these substances are dissolved in water, they separate into their component ions. So, when the two aqueous compounds are initially combined, four types of ions are present in the solution. These ions are free to react and combine with one another. Looking at the reaction equation, we can see that a solid, silver chromate, is formed. This insoluble product is known as a precipitate. The reaction also produces ammonium nitrate, which is aqueous.
As silver chromate is insoluble in water, it will not separate into its component ions, but ammonium nitrate is soluble in water. So, after the ions have reacted, there will still be ammonium and nitrate ions present in the solution. So we can see that although a reaction has occurred, the ammonium and nitrate ions did not take part in the chemical reaction. Therefore, these ions are the spectator ions. So the spectator ions for the given reaction are NO3− and NH4+, answer choice (C).
