CIE iGCSE Co-Ordinated Science C3.1 Formulas Exam Style Questions Paper 3
Question
iron
magnesium
potassium
sodium
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
Topic codes:
• Topic C3.1 — Formulas (Part (a)(i) & (a)(ii))
• Topic C6.2 — Rate of reaction (Part (b)(i), (b)(ii), (b)(iv) & (c))
• Topic C12.4 — Separation and purification (Part (b)(iii))
• Topic C1.1 — Solids, liquids and gases (Part (c))
▶️ Answer/Explanation
(a)(i) 3 different elements
Calcium carbonate (CaCO₃) contains three different elements: calcium (Ca), carbon (C), and oxygen (O).
(a)(ii) 5 atoms
The formula CaCO₃ shows 1 calcium atom, 1 carbon atom, and 3 oxygen atoms. Total atoms = 1 + 1 + 3 = 5.
(b)(i) Stopwatch / timer / clock
To investigate the rate of reaction, the student needs to measure the time taken for the reaction to proceed. A stopwatch, timer, or clock is required to record time intervals.
(b)(ii) Carbon dioxide gas is lost from the conical flask.
The reaction produces carbon dioxide gas, which escapes from the open flask into the atmosphere. This loss of gas causes the total mass of the flask and its contents to decrease.
(b)(iii) Filtration
Filtration is used to separate an insoluble solid (unreacted calcium carbonate) from a liquid (calcium chloride solution). The solid remains on the filter paper as residue, and the solution passes through as filtrate.
(b)(iv) Two changes to increase the rate of reaction:
- Increase concentration of the acid — more acid particles per unit volume lead to more frequent collisions with calcium carbonate particles.
- Increase temperature of the acid — particles have more kinetic energy, leading to more frequent and more energetic collisions.
- Increase surface area of calcium carbonate — using powder instead of lumps exposes more particles to the acid, increasing collision frequency.
(c) A represents solid calcium carbonate because particles are touching and have a regular arrangement.
In a solid, particles are closely packed in a fixed, regular lattice structure. The strong forces between particles keep them in fixed positions, giving solids a definite shape and volume.
C represents carbon dioxide gas because particles are widely spaced and have a random arrangement.
In a gas, particles are far apart with no regular arrangement. They move rapidly and randomly in all directions, filling the available space. The weak forces between particles allow them to move freely.