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CIE iGCSE Co-Ordinated Science C9.4 Reactivity series Exam Style Questions Paper 3

CIE iGCSE Co-Ordinated Science Paper 3 - All Chapters

Question

(a) Fig. 7.1 shows the arrangement of atoms in pure aluminium metal and in a mixture of aluminium and magnesium.
(i) State the name used to describe a mixture of metals.
(ii) Calculate the percentage of magnesium atoms in the mixture of metals shown in Fig. 7.1.
(b) The metals in the list are extracted from their ores.
copper
iron
magnesium
potassium
sodium
Identify one metal from the list that is not able to be extracted from its ore by heating with carbon.
(c) A student investigates the reaction, if any, of four metals W, X, Y and Z with dilute hydrochloric acid.
The student places pieces of the different metals into separate test-tubes containing dilute hydrochloric acid.
Bubbles of gas are observed as shown in Fig. 7.2.
The four metals are copper, iron, magnesium and zinc.
Use the information in Fig. 7.2 and your knowledge of the reactivity series to identify the metals W, X, Y and Z.
(d) The symbol equation for one of the reactions observed in Fig. 7.2 is
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
(i) Complete the word equation for this reaction.
………………………….. + hydrochloric acid → ………………………….. + …………………………..
(ii) State what (aq) means in the symbol equation.

Most-appropriate topic codes (Cambridge IGCSE Coordinated Sciences 0654):

• Topic C9.3 — Alloys and their properties (Part (a)(i))
• Topic C9.3 — Alloys and their properties (Part (a)(ii))
• Topic C9.4 — Reactivity series (Part (b))
• Topic C9.4 — Reactivity series (Part (c))
• Topic C3.1 — Formulas (Part (d)(i))
• Topic C3.1 — Formulas (Part (d)(ii))

▶️ Answer/Explanation

(a)(i) alloy
An alloy is a mixture of a metal with other elements. Alloys often have improved properties compared to pure metals, such as increased strength.

(a)(ii) 3 magnesium atoms out of 20 total or 3/20; 15(%)
The diagram shows 3 magnesium atoms (dark) out of 20 total atoms. Percentage = (3/20) × 100 = 15%.

(b) sodium or magnesium or potassium; more reactive than carbon / higher than carbon in the reactivity series
Metals above carbon in the reactivity series cannot be extracted by reduction with carbon because they form stable compounds that carbon cannot reduce. Sodium, magnesium, and potassium are all more reactive than carbon.

(c) W magnesium; X zinc; Y iron; Z copper
Magnesium is the most reactive and produces bubbles most vigorously. Zinc reacts moderately. Iron reacts slowly. Copper does not react with dilute hydrochloric acid as it is below hydrogen in the reactivity series.

(d)(i) magnesium + hydrochloric acid → magnesium chloride + hydrogen
The word equation shows the reactants and products using their names. Magnesium displaces hydrogen from hydrochloric acid forming magnesium chloride and hydrogen gas.

(d)(ii) aqueous or (in) solution or dissolved in water
The state symbol (aq) indicates that the substance is dissolved in water to form an aqueous solution.

Question

(a) The list shows six metals.
aluminium       calcium       iron       magnesium       platinum       sodium
Identify the metal from the list that is:
(i) extracted from bauxite
(ii) an alkali metal
(iii) the main element in steel
(iv) used as inert electrodes in electrolysis.
(b) A student investigates the reaction between dilute hydrochloric acid and magnesium. The symbol equation for this reaction is:
\[\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\]
(i) Name one product from this reaction.
(ii) The concentration of the dilute hydrochloric acid used is \(36.5 \, \text{g/dm}^3\). The experiment is repeated using acid with a concentration of \(73.0 \, \text{g/dm}^3\).
State the effect on the rate of reaction. Explain your answer.
(iii) Name a metal in the reactivity series that is more reactive than magnesium.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C9.6 — Extraction of metals (Part (a)(i))
• Topic C8.2 — Group I properties (Part (a)(ii))
• Topic C9.1 — Properties of metals (Part (a)(iii))
• Topic C4.1 — Electrolysis (Part (a)(iv))
• Topic C7.1 — Characteristic properties of acids (Parts (b)(i), (b)(ii), (b)(iii))
• Topic C9.4 — Reactivity series (Part (b)(iii))

▶️ Answer/Explanation

(a)(i) aluminium

Bauxite is the main ore of aluminium. Aluminium is extracted from bauxite by electrolysis because it is a reactive metal.

(a)(ii) sodium

Sodium is an alkali metal found in Group I of the Periodic Table. The other alkali metals include lithium and potassium.

(a)(iii) iron

Steel is an alloy made primarily of iron with small amounts of carbon and other elements such as chromium and nickel.

(a)(iv) platinum

Platinum is used as an inert electrode in electrolysis because it is unreactive and does not participate in the reaction.

(b)(i) magnesium chloride / hydrogen

The products of the reaction between magnesium and hydrochloric acid are magnesium chloride (a salt) and hydrogen gas.

(b)(ii) effect on rate of reaction: increases

Explanation: The concentration of the acid has doubled from \(36.5 \, \text{g/dm}^3\) to \(73.0 \, \text{g/dm}^3\). Increasing the concentration means there are more reactant particles per unit volume. This leads to a higher frequency of successful collisions between magnesium atoms and hydrogen ions, thereby increasing the rate of reaction.

(b)(iii) calcium / sodium / potassium

Calcium, sodium and potassium are all more reactive than magnesium in the reactivity series. These metals react more vigorously with dilute acids and water compared to magnesium.

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