CIE iGCSE Co-Ordinated Science C7.3 Preparation of salts Exam Style Questions Paper 3
Question
ammonium nitrate
carbon dioxide
lead bromide
sodium chloride
sulfur dioxide
Each compound may be used once, more than once or not at all.
State which compound:
State three general physical properties of solid metals.
Table 2.1 shows the percentage composition of duralumin.
Explain why duralumin does not have a precise melting point.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C2.1 — Elements, compounds and mixtures (Part (a)(i))
• Topic C7.3 — Preparation of salts (Part (a)(ii))
• Topic C7.2 — Oxides (Part (a)(iii))
• Topic C10.2 — Air quality and climate (Part (a)(iv))
• Topic C9.6 — Extraction of metals (Part (a)(v))
• Topic C9.1 — Properties of metals (Part (b))
• Topic C9.3 — Alloys and their properties (Part (c))
▶️ Answer/Explanation
(a)(i) lead bromide
Lead has a \(2+\) charge and bromide has a \(1-\) charge.
Two bromide ions balance one lead ion, giving \(\text{PbBr}_2\).
(a)(ii) ammonium nitrate
Ammonium salts react with alkalis to release ammonia gas on heating.
Ammonium nitrate is the only ammonium salt in the list.
(a)(iii) carbon dioxide / sulfur dioxide
Non-metal oxides dissolve in water to form acidic solutions.
Both \(\text{CO}_2\) and \(\text{SO}_2\) are non-metal oxides, so either is accepted.
(a)(iv) carbon dioxide
\(\text{CO}_2\) absorbs infrared radiation reflected from the Earth’s surface.
This traps thermal energy in the atmosphere, contributing to the greenhouse effect.
(a)(v) aluminium oxide
Bauxite is the ore from which aluminium is extracted.
Its main component is aluminium oxide, \(\text{Al}_2\text{O}_3\).
(b) Any three from: conducts heat, conducts electricity, malleable, high melting/boiling point
Solid metals share physical properties due to metallic bonding.
Free-moving delocalised electrons allow good thermal and electrical conductivity.
The regular layered structure allows metals to be bent or hammered into shape (malleable).
(c)(i) 19 kg
Aluminium makes up 95% of the alloy by mass.
Mass of aluminium \( = \dfrac{95}{100} \times 20 = 19 \, \text{kg}\).
(c)(ii) Duralumin is not a pure substance
Duralumin is a mixture (alloy) of aluminium, copper and magnesium, not a single pure substance.
Each component metal has a different melting point.
The mixture therefore melts gradually over a range of temperatures rather than at one fixed point.
Question
Draw one straight line from each word to its correct description.
Fig. 2.1 shows the apparatus the student uses.
Calculate the rate at which carbon dioxide is made in \(\text{cm}^3/\text{s}\).
State the number of different elements present in calcium carbonate.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topics C2.1, C2.4, C12.3 — Elements/compounds/mixtures, Ions and ionic bonds, Chromatography (Part (a))
• Topic C12.1 — Experimental design (Part (b)(i))
• Topic C7.3 — Preparation of salts (Part (b)(ii))
• Topic C12.5 — Identification of ions and gases (Part (b)(iii))
• Topic C6.2 — Rate of reaction (Parts (b)(iv), (b)(v))
• Topic C2.1 — Elements, compounds and mixtures (Part (b)(vi))
▶️ Answer/Explanation
(a)
Ion is an atom that has gained or lost electrons.
Sodium is an element in Group I of the Periodic Table.
Solute is a substance that dissolves in a solvent.
Chromatography is a technique used to separate dyes.
Sulfur is used in the production of sulfuric acid.
(b)(i) Measuring cylinder
Apparatus A is used to collect and measure the volume of gas produced by downward displacement of water.
Its graduated scale allows the volume of carbon dioxide to be read directly.
(b)(ii) Calcium chloride
Calcium carbonate reacts with hydrochloric acid to form a calcium salt.
Since hydrochloric acid is used, the salt formed is calcium chloride.
(b)(iii) Bubble the gas through limewater; it turns milky/cloudy
Carbon dioxide is tested for by bubbling the gas through limewater.
A positive result is shown by the limewater turning milky or cloudy.
(b)(iv) 1.8 cm³/s
Rate = volume ÷ time.
Rate = \(\dfrac{90 \, \text{cm}^3}{50 \, \text{s}} = 1.8 \, \text{cm}^3/\text{s}\).
(b)(v) Lower temperature of acid; lower concentration of acid (or decrease surface area)
Reducing the temperature of the acid slows down particle collisions, reducing the rate.
Reducing the concentration of the acid also lowers the frequency of successful collisions.
Alternatively, decreasing the surface area of the calcium carbonate would reduce the rate.
(b)(vi) 3
The formula \(\text{CaCO}_3\) contains calcium (Ca), carbon (C), and oxygen (O).
This gives a total of 3 different elements.