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CIE iGCSE Co-Ordinated Science C6.1 Physical and chemical changes Exam Style Questions Paper 4

CIE iGCSE Co-Ordinated Science Paper 4 - All Chapters

Question

Iron is extracted from hematite by reduction of iron(III) oxide in a blast furnace.
(a) Iron(III) oxide reacts with carbon monoxide.
Complete the equation for the reduction of iron(III) oxide.
\( \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow \text{……} + \text{……} \)
(b) The iron made in the blast furnace is an alloy containing about 90–95% iron.
Fig. 8.1 shows pure iron and the iron made in the blast furnace.
(i) Complete the sentences.
Pure iron is an element because ………………………………
Iron from the blast furnace is a mixture because ………………………………
(ii) Iron from the blast furnace is harder than pure iron.
Explain why. Use Fig. 8.1 to help you.
(iii) Pure iron is very malleable.
Explain why. Use Fig. 8.1 to help you.
(c) Calcium carbonate, \( \text{CaCO}_3 \), is added to the blast furnace to remove impurities.
(i) The calcium carbonate is heated to make calcium oxide, CaO.
The equation for the reaction is shown.
\( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)
State the name of the type of reaction that occurs.
(ii) The calcium oxide reacts with silicon dioxide, \( \text{SiO}_2 \), which is an impurity in the iron ore, to make calcium silicate.
\( \text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3 \)
Calculate the minimum mass of calcium oxide needed to remove 720 tonnes of silicon dioxide.
\( [A_r: \text{Ca}, 40; \text{O}, 16; \text{Si}, 28] \)
(iii) Fig. 8.2 shows the structure and bonding in silicon dioxide.
The structure and bonding is similar to diamond.
State the type of structure and bonding in silicon dioxide.
Choose from the list.
• giant ionic
• giant covalent
• giant metallic
• simple covalent

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

• Topic C9.6 — Extraction of metals / Blast furnace (Part (a))
• Topic C9.3 — Alloys and their properties (Part (b)(i), (b)(ii) & (b)(iii))
• Topic C6.1 — Physical and chemical changes / Thermal decomposition (Part (c)(i))
• Topic C3.2 — Relative masses / Stoichiometry (Part (c)(ii))
• Topic C2.6 — Giant covalent structures (Part (c)(iii))

▶️ Answer/Explanation

(a) \( \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \)

Carbon monoxide reduces iron(III) oxide to iron metal, being oxidised to carbon dioxide. The equation is balanced with 2 Fe, 3 C, and 6 O atoms on both sides.

(b)(i) Pure iron is an element because it is made of only one type of atom. Iron from the blast furnace is a mixture because it contains two elements (iron and carbon/silicon) that are not chemically combined.

An element consists of identical atoms, while a mixture contains different substances that are not chemically bonded together.

(b)(ii) Iron from the blast furnace is harder because the atoms are different sizes, which prevents the layers of atoms from sliding over each other (unlike in pure iron where all atoms are the same size).

The different-sized atoms in the alloy disrupt the regular arrangement of layers, making it harder for them to slip past one another.

(b)(iii) Pure iron is malleable because layers of atoms can slide / move / slip over each other when a force is applied.

The regular, identical layers of atoms in pure iron can easily slide past one another, allowing the metal to be hammered or bent into shape.

(c)(i) Thermal decomposition

Calcium carbonate breaks down into calcium oxide and carbon dioxide when heated, which is a thermal decomposition reaction.

(c)(ii) Mass of CaO = 672 tonnes

\( M_r(\text{CaO}) = 40 + 16 = 56 \)
\( M_r(\text{SiO}_2) = 28 + (2 \times 16) = 60 \)
\( \text{Mass of CaO} = \frac{56}{60} \times 720 = 672 \text{ tonnes} \)
The mole ratio between CaO and SiO₂ is 1:1, so the mass of CaO needed is proportional to the ratio of their formula masses.

(c)(iii) Giant covalent

Silicon dioxide has a giant covalent structure similar to diamond, where each silicon atom is bonded to four oxygen atoms in a tetrahedral arrangement.

Question

A student heats three substances X, Y and Z in a water-bath. Table 2.1 shows the state of the three substances before heating, during heating and after cooling.
(a) Draw one line from substance X and one line from substance Y to show the arrangement of the particles before heating.
(b) Describe the difference in the movement of the particles in a solid and in a liquid.
(c) Explain how we know that the change to substance X is a physical change and not a chemical change.
(d) Substance Z is the ionic compound sodium chloride, NaCl. Draw a dot-and-cross diagram to show the ionic bonding in sodium chloride.
(e) Fig. 2.1 shows the electrolysis of concentrated aqueous sodium chloride. Complete the three labels on Fig. 2.1 to show the products made.

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

• Topic C1.1 — States of matter, particle theory (Parts (a), (b))
• Topic C6.1 — Physical and chemical changes (Part (c))
• Topic C2.4 — Ions and ionic bonds (Part (d))
• Topic C4.1 — Electrolysis (Part (e))

▶️ Answer/Explanation

(a) X (solid before heating) connects to the regular, closely-packed particle diagram; Y (liquid before heating) connects to the closely-packed, disordered particle diagram.

X is a solid before heating, so its particles are arranged in a regular pattern.
Y is already a liquid before heating, so its particles are close together but randomly arranged.

(b) Solid: particles vibrate about fixed positions. Liquid: particles move around/slide over each other.

In a solid, particles only vibrate in place and cannot change position.
In a liquid, particles have enough energy to move past one another while staying close together.

(c) It is reversible and no new substance is formed.

Melting and solidifying are reversible processes, unlike a chemical change.
Since substance X returns to a solid identical to the original on cooling, no new substance has been formed.

(d) \(\text{Na}^{+}\) has no outer electrons shown (transferred away); \(\text{Cl}^{-}\) shows 8 outer electrons (7 of its own plus 1 from Na, shown as a cross).

Sodium loses one electron to form \(\text{Na}^{+}\), leaving an empty outer shell.
Chlorine gains that electron to form \(\text{Cl}^{-}\), giving it a full outer shell of 8 electrons.
Square brackets with charges (+ and −) are drawn around each ion.

(e) Anode (top left): chlorine; Cathode (top right): hydrogen; Bottom outlet: sodium hydroxide.

Chlorine gas is released at the positive electrode (anode).
Hydrogen gas is released at the negative electrode (cathode).
Sodium hydroxide solution remains/forms in the electrolyte and drains from the bottom.

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