CIE iGCSE Co-Ordinated Science C9.5 Corrosion of metals Exam Style Questions Paper 3
Question
(a) (i) An iron nail rusts when it is exposed to damp air.
Rusting involves the oxidation of iron.
State what is meant by the term oxidation.
(ii) Describe one method used to prevent the iron nail from rusting.
Explain how this method prevents the iron nail from rusting.
method …………………………………………………………………………
explanation …………………………………………………………………………
(b) Complete the sentence.
Metal ores are a finite resource and therefore, metals need to be ……………………………… .
(c) Iron is a transition element.
Put a tick (3) in the boxes next to all the correct statements about iron.
(d) Steel is an alloy of iron.
(i) Suggest why steel is used for making cars instead of pure iron.
(ii) Table 2.1 shows the percentage composition of stainless steel.
Calculate the mass of iron contained in 80 kg of stainless steel.
mass of iron = ……………………………………………. kg
(e) Iron is malleable.
State the meaning of malleable.
▶️Answer/Explanation
Ans : 2(a)(i) gain of oxygen ;
2(a)(ii) paint it ;
stops contact with air and water ; etc.
2(b) recycled ; OWTTE
2(c) iron acts as a catalyst ;
iron forms coloured compounds ;
2(d)(i) stronger ;
2(d)(ii) iron % 65 ;
80 × 65 / 100 = 52 (kg) ;
2(e) can be shaped or bent ;
Question
(a) State the name given to mixtures made from a metal with other elements.
(b) Iron is an element in Period 4 of the Periodic Table.
State the name of the collection of metals in Period 4 that contains iron.
(c) Describe the test used to identify iron(II) ions and give the observation for a positive result.
test ………………………………………………………………….
observation …………………………………………………….
(d) State the two substances that react with iron to make rust.
1 …………………………………………………………………………
2 ……………………………………………………………………….
(e) An isotope of iron has a proton number of 26 and a nucleon number of 58.
(i) Deduce the number of neutrons and the number of electrons in this isotope of iron.
neutrons = ………………………………………………………
electrons = ………………………………………………………
(ii) State the meaning of the term isotope.
(f) A teacher reacts dilute hydrochloric acid with four metals.
The observations are shown in Table 11.1.
Place the four metals in order of their reactivity from the most reactive to the least reactive.
most reactive ……………………………………………………………………..
least reactive ………………………………………………………………………
▶️Answer/Explanation
Ans : 11(a) alloy ;
11(b) transition elements / metals ;
11(c) aqueous sodium hydroxide ;
green precipitate ;
11(d) oxygen ;
water ;
11(e)(i) neutrons = 32 ;
electrons = 26 ;
11(e)(ii) atoms of the same element that have different numbers of neutrons ;
11(f) lithium calcium iron silver lithium and / or silver correct ;
all else correct ;
Question
(a) Fig. 11.1 shows iron rusting.
(i) Iron rusts when two other substances are present. State the names of these two substances.
▶️Answer/Explanation
Answer: Oxygen and water.
Explanation: Rusting of iron is a chemical reaction that occurs when iron is exposed to both oxygen and water. The reaction forms iron oxide, commonly known as rust.
(ii) Describe and explain one method used to prevent the rusting of iron.
▶️Answer/Explanation
Answer: Painting or coating the iron with a protective layer.
Explanation: Painting or coating the iron creates a barrier that prevents oxygen and water from coming into contact with the iron surface, thus preventing rusting. This method is commonly used in industries and for household items like gates and railings.
(b) Stainless steel is an alloy of iron.
State one use for stainless steel.
▶️Answer/Explanation
Answer: Cutlery (knives, forks, spoons).
Explanation: Stainless steel is widely used in cutlery because it is resistant to rust and corrosion, making it durable and hygienic for food preparation and consumption.
(c) Solid iron melts at 1538 °C to become liquid (molten) iron.
Describe one difference in the properties of a solid compared to a liquid.
▶️Answer/Explanation
Answer: A solid has a fixed shape, while a liquid takes the shape of its container.
Explanation: In a solid, the particles are tightly packed and have a fixed arrangement, giving the solid a definite shape. In a liquid, the particles are less tightly packed and can move around, allowing the liquid to flow and take the shape of its container.
(d) Melting is one of the processes involved when a substance changes state.
Fig. 11.2 shows other processes involved when substances change state.
Identify processes A, B, and C.
▶️Answer/Explanation
Answer:
- A: Boiling
- B: Condensing
- C: Freezing
Explanation:
- Boiling (A): The process by which a liquid turns into a gas at its boiling point.
- Condensing (B): The process by which a gas turns into a liquid.
- Freezing (C): The process by which a liquid turns into a solid at its freezing point.
Question
Metal oxides are formed when metals and oxygen react. Fig. 2.1 shows how magnesium oxide is formed.
(a)(i) The reaction releases thermal (heat) energy. State the term used to describe a chemical reaction that releases thermal energy.
▶️Answer/Explanation
Answer: Exothermic
Explanation: An exothermic reaction is a chemical reaction that releases energy in the form of heat. In this case, the formation of magnesium oxide from magnesium and oxygen releases thermal energy, making it an exothermic reaction.
(ii) Balance the symbol equation for the formation of magnesium oxide.
▶️Answer/Explanation
Answer: \(2Mg + O_2 \rightarrow 2MgO\)
Explanation: The balanced equation shows that two magnesium atoms react with one oxygen molecule to form two magnesium oxide molecules, ensuring the conservation of mass.
(b) Describe two physical properties of magnesium.
▶️Answer/Explanation
Answer: Magnesium is malleable and a good conductor of electricity.
Explanation: Magnesium is a metal that can be easily shaped (malleable) and allows the flow of electric current (good conductor). These properties are typical of many metals.
(c) Excess aqueous hydrochloric acid is added to magnesium and to magnesium oxide as shown in Fig. 2.2.
(i) Magnesium and magnesium oxide both react with aqueous hydrochloric acid. Describe one difference and one similarity in the observations made.
▶️Answer/Explanation
Answer: Difference: Gas is released with magnesium but not with magnesium oxide. Similarity: Both solids dissolve to form a soluble product.
Explanation: Magnesium reacts with hydrochloric acid to produce hydrogen gas, while magnesium oxide does not produce gas. However, both reactions result in the formation of a soluble product, magnesium chloride.
(ii) One of the products made in both reactions in (c)(i) is the same. State the name of this product.
▶️Answer/Explanation
Answer: Magnesium chloride (MgCl₂)
Explanation: Both magnesium and magnesium oxide react with hydrochloric acid to form magnesium chloride as the product.
(d) Aqueous hydrochloric acid is added to copper and to copper(II) oxide. There is no reaction between the hydrochloric acid and copper.
Copper(II) oxide reacts and dissolves in the acid.
(i) Explain why there is no reaction between copper and dilute acid. Use ideas about the relative positions of elements in the reactivity series.
▶️Answer/Explanation
Answer: Copper is less reactive than hydrogen.
Explanation: In the reactivity series, copper is below hydrogen, meaning it cannot displace hydrogen from acids. Therefore, copper does not react with dilute acids.
(ii) Predict whether the solution formed when copper(II) oxide reacts with the acid is coloured or is colourless. Explain your answer.
▶️Answer/Explanation
Answer: The solution is coloured.
Explanation: Copper(II) oxide reacts with acid to form copper(II) ions, which are typically blue or green in solution, indicating that the solution will be coloured.
(e) Rust is formed when iron reacts with oxygen and another substance.
(i) State the name of the other substance that must be present for iron to rust.
▶️Answer/Explanation
Answer: Water (or water vapour)
Explanation: Rusting of iron requires both oxygen and water. Without water, the reaction cannot proceed.
(ii) Barrier methods are used to prevent rusting. Name one substance used in the barrier method of rust prevention.
▶️Answer/Explanation
Answer: Paint
Explanation: Paint acts as a barrier, preventing oxygen and water from coming into contact with the iron, thus preventing rust.
(iii) State one way, other than forming a barrier, that prevents iron from rusting.
▶️Answer/Explanation
Answer: Making it into an alloy (e.g., stainless steel)
Explanation: Alloying iron with other metals, such as chromium, creates stainless steel, which is more resistant to rusting.