Cambridge Secondary (7-9). Stage 9. MCE Science. Student Book - Unit 6: Displacement Reactions

Heavy metal contamination in water poses risks to humans and ecosystems. Displacement reactions can remove less reactive toxic metals from solution using a more reactive metal. Besides cleaning water sources, what are the benefits of using displacement reactions to deal with heavy metal contamination?

Think of two objects. One is made of a shiny metal (such as silver jewellery) and the other rusts easily (such as iron nails). What do you think causes the bright metal to stay shiny and the other metal to rust? Think about the environmental factors and the nature of the metal itself.

Think of two objects. One is made of a shiny metal (such as silver jewellery) and the other rusts easily (such as iron nails). Is there a way to predict which metals will rust and which will stay shiny?

Figure 6.3 shows a rocket being launched by the reaction of zinc with sulfur.



Why do you think it is helpful to represent the reaction using a word equation?

Figure 6.3 shows a rocket being launched by the reaction of zinc with sulfur.



Why is it helpful to write a symbol equation for this reaction?

Write the following description as a word equation.

Iron reacts with oxygen in the air and rust is formed.

Write the following description as a word equation.

Adding sodium oxide to water produces sodium hydroxide.

Write the following description as a word equation.

Iron can react with sulfur when they are heated together. The reaction forms a substance called iron sulfide that smells like rotting eggs.

Write the following description as a word equation.

Zinc and sulfur react to form zinc sulfide.

Look at these symbol equations. Which of these match with which of the word equations you wrote earlier?

Word descriptions: **1a** iron + oxygen → iron oxide; **1b** sodium oxide + water → sodium hydroxide; **1c** iron + sulfur → iron sulfide; **1d** zinc + sulfur → zinc sulfide.

**a** $\mathrm{Zn+S\rightarrow ZnS}$

**b** $\mathrm{Na_2O+H_2O\rightarrow2NaOH}$

**c** $\mathrm{4Fe+3O_2\rightarrow2Fe_2O_3}$

**d** $\mathrm{Fe+S\rightarrow FeS}$

Sodium and water react to form sodium hydroxide and hydrogen. Write the word equation for this reaction.

Sodium and water react to form sodium hydroxide and hydrogen. What are the reactants?

Sodium and water react to form sodium hydroxide and hydrogen. What are the products?

When calcium carbonate is heated, it breaks down into calcium oxide and carbon dioxide. Write the word equation for the reaction.

When calcium carbonate is heated, it breaks down into calcium oxide and carbon dioxide. Write the symbol equation for the reaction.

You have learnt that some metals react with water while others do not. Using the concept of displacement and the reactivity series below, explain why magnesium reacts with steam but copper does not.

Understanding how reactive an element is helps you choose safe experiment materials. It also helps you predict the reaction intensity to avoid hazardous situations. Can you think of another reason why understanding reactivity is important for safety? In pairs, discuss your ideas.

Your teacher demonstrates the following investigation. Two test tubes A and B each contain 10 ml of freshly prepared copper sulfate solution. A cleaned grey iron nail is immersed in B; a second nail is kept on white paper for comparison. After 20 minutes the immersed nail is removed and placed beside the other nail. Wear suitable gloves and safety goggles; do not touch or ingest chemicals.



Record your observations.

Your teacher demonstrates the following investigation. Two test tubes A and B each contain 10 ml of freshly prepared copper sulfate solution. A cleaned grey iron nail is immersed in B; a second nail is kept on white paper for comparison. After 20 minutes the immersed nail is removed and placed beside the other nail. Wear suitable gloves and safety goggles; do not touch or ingest chemicals.



What does the brown coating on the iron nail tell you about the reaction?

Your teacher demonstrates the following investigation. Two test tubes A and B each contain 10 ml of freshly prepared copper sulfate solution. A cleaned grey iron nail is immersed in B; a second nail is kept on white paper for comparison. After 20 minutes the immersed nail is removed and placed beside the other nail. Wear suitable gloves and safety goggles; do not touch or ingest chemicals.



What colour change do you observe in the copper sulfate solution?