Problem 7 - Chemistry: The Central Science in SI Units, Global Edition

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]

Step-by-Step Solution

Answer

To identify the metal powders, perform reactions with the given solutions and observe their behavior: 1. React samples with 1M sodium nitrate: - Zinc forms zinc nitrate and sodium. - Lead and Platinum do not react. 2. React samples with 1M nitric acid: - Zinc and Lead form zinc nitrate and lead nitrate with hydrogen gas, respectively. - Platinum does not react. 3. React samples with 1M nickel nitrate: - Zinc forms zinc nitrate and nickel. - Lead and Platinum do not react. Finally, identify the metal powders based on reactivity: - Zinc reacts with all three solutions. - Lead reacts only with nitric acid. - Platinum does not react with any solution.

Step 1: Understanding the Reactivity Series

The Reactivity Series of metals is a list of elements organized by their reactivity, with the most reactive metals at the top and least reactive at the bottom. The order of reactivity for the given metals in this exercise is: Zinc > Lead > Platinum. Platinum being the least reactive metal will not react with any of the given solutions while zinc being the most reactive will react with most of them.

Step 2: Reacting with Sodium Nitrate

Add a portion of each metal powder to three separate test tubes. Then add 1M sodium nitrate solution to each test tube. Observe the reactions: - Zinc will react with sodium nitrate to form zinc nitrate and sodium. - Lead will not react with sodium nitrate since its reactivity is lower. - Platinum will not react with sodium nitrate as it's the least reactive.

Step 3: Reacting with Nitric Acid

Add a portion of each metal powder to three new test tubes. Then add 1M nitric acid solution to each test tube. Observe the reactions: - Zinc will react with nitric acid to form zinc nitrate and hydrogen gas. - Lead will react with nitric acid to form lead nitrate and hydrogen gas. - Platinum will not react with nitric acid due to its low reactivity.

Step 4: Reacting with Nickel Nitrate

Add a portion of each metal powder to three new test tubes. Then add 1M nickel nitrate solution to each test tube. Observe the reactions: - Zinc will react with nickel nitrate to form zinc nitrate and nickel. - Lead will not react with nickel nitrate since its reactivity is lower. - Platinum will not react with nickel nitrate as it's the least reactive.

Step 5: Identifying the Metal Powders

Based on the observations from the reactions with the three solutions, we can determine the identities of the metal powders: - Zinc will react with all three solutions (sodium nitrate, nitric acid, and nickel nitrate). - Lead will only react with nitric acid. - Platinum will not react with any of the solutions. Thus, by observing which metal powder reacts with which solutions, we can identify the contents of the three bottles.

Key Concepts

Metal Identification

To identify metals when their labels have fallen off can be tricky but possible by using simple chemical tests. In this exercise, we are tasked with identifying zinc, lead, and platinum using three different solutions. The key here is to understand each metal’s reactivity and how they respond to certain chemicals. By observing reactions that occur or don't occur, you can determine which metal is which.

It's important to carefully observe these tests and record any noticeable changes like bubbling, change in color, or absence of any reaction. Each metal will show distinct reactions based on its chemical properties, which you can use to deduce its identity.

Chemical Reactions

Chemical reactions are processes where substances change into new forms by breaking and forming bonds. In these experiments, the reactions help reveal the identity of unknown metals based on their different reactivity with sodium nitrate, nitric acid, and nickel nitrate.

Here's what happens in each case:

• With sodium nitrate, zinc reacts, while lead and platinum do not.
• With nitric acid, both zinc and lead react, producing hydrogen gas, but platinum remains unreactive.
• With nickel nitrate, zinc reacts by swapping places with nickel, highlighting its higher reactivity compared to nickel and platinum.

Understanding these interactions helps us see the chemical principles in play, such as how metals react based on their position in the Reactivity Series.

Metal Reactivity

Metal reactivity affects how metals engage in chemical reactions, a concept central to identifying our unknown metal powders. The Reactivity Series orders metals by their eagerness to donate electrons and form positive ions (cations). In general, the higher a metal on the series, the more reactive it is.

Zinc sits higher than lead and platinum on this scale, making it more reactive. This is why zinc readily reacts with all of the solutions tested. In contrast, lead shows reactivity only with nitric acid, pointing to its moderate position in the series. Platinum, being at the bottom of the reactivity scale, doesn't react with the provided solutions, highlighting its noble nature. These relative differences in reactivity guide us to distinguish one metal powder from another effectively.

Solutions and Solubility

Understanding solutions and solubility is key when considering chemical reactions. Solutions like sodium nitrate, nitric acid, and nickel nitrate enable metals to show their reactivity. In this experiment:

- **Solutions** act as a medium for reactions to occur. They provide ions that can participate in chemical changes with the metal powders.

- **Solubility** determines how much of a substance will dissolve in a solution. But, in this context, it’s more about the metal’s ability to interact with the solution rather than dissolve directly.

When a metal reacts with the solution, such as zinc with nitric acid, the metal appears to dissolve as it forms a new soluble compound, like zinc nitrate. These transformations, visible as changes in the test tubes, help us conclude which metal is present based on its solubility and reactivity.