Question

The labels have fallen off three bottles containing powdered samples of metals; one contains zinc, one lead, and the other platinum. You have three solutions at your disposal: \(1 \mathrm{M}\) sodium nitrate, \(1 \mathrm{M}\) nitric acid, and \(1 \mathrm{M}\) nickel nitrate. How could you use these solutions to determine the identities of each metal powder? [Section 4.4]

Short answer

To identify the metal powders, use the provided solutions and observe the reactions. First, test each metal with \(1\mathrm{M}\) sodium nitrate: zinc and lead will react and form a precipitate, while platinum will not react. Second, test each metal with \(1\mathrm{M}\) nitric acid: zinc will react more vigorously than lead, and both will produce hydrogen gas. Platinum will not react with sodium nitrate, zinc will react more vigorously with nitric acid than lead, and both zinc and lead will react with nickel nitrate.

Step-by-step solution

Observe the reactivity series

Recall the reactivity series for metals: the higher the metal is in the series, the more likely it is to react. Zinc is more reactive than lead, which in turn is more reactive than platinum.

Test each metal with sodium nitrate

Mix a small sample of each metal with the \(1\mathrm{M}\) sodium nitrate solution. Since zinc and lead are more reactive than sodium, they will react and form a precipitate, whereas platinum will not react. Zinc reaction: \(Zn(s) + 2NaNO_3(aq) \rightarrow Zn(NO_3)_2(aq) + 2Na(s)\) Lead reaction: \(Pb(s) + 2NaNO_3(aq) \rightarrow Pb(NO_3)_2(aq) + 2Na(s)\) The metal that does not react with sodium nitrate is platinum.

Test each metal with nitric acid

Mix a small sample of each metal with the \(1\mathrm{M}\) nitric acid solution. Both zinc and lead will react with nitric acid, forming a nitrate salt and hydrogen gas. However, the rate of reaction differs between zinc and lead. Zinc reaction: \(Zn(s) + 2HNO_3(aq) \rightarrow Zn(NO_3)_2(aq) + H_2(g)\) Lead reaction: \(Pb(s) + 2HNO_3(aq) \rightarrow Pb(NO_3)_2(aq) + H_2(g)\) The metal that reacts more vigorously with nitric acid is zinc, while the one that reacts less vigorously is lead.

Test each metal with nickel nitrate

Although this step is not necessary, it acts as a confirmation. Mix a small sample of each metal with the \(1\mathrm{M}\) nickel nitrate solution. Platinum will not react with nickel nitrate, while zinc and lead will form a precipitate. To summarize, you can identify the metal powders in the bottles by observing their reactions with the given solutions: platinum will not react with sodium nitrate, zinc will react more vigorously with nitric acid than lead, and both zinc and lead will react with nickel nitrate.