CIE iGCSE Co-Ordinated Science C11.1 Formulas and terminology Exam Style Questions Paper 3
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.1 — Formulas and terminology (Part (a)(i))
• Topic C11.5 — Alkenes (Part (a)(ii) & (b)(i))
• Topic C11.7 — Polymers (Part (b)(ii))
▶️ Answer/Explanation
(a)(i) Ethene contains only carbon and hydrogen atoms.
Hydrocarbons are compounds that consist exclusively of carbon and hydrogen. Ethene has the formula \(\mathrm{C_2H_4}\), so it fits this definition.
(a)(ii) Correct displayed formula of ethene:
The structure must show a double bond between the two carbon atoms, with each carbon atom bonded to two hydrogen atoms. The double bond is essential because ethene is an unsaturated hydrocarbon.
(b)(i) from orange to colourless
Aqueous bromine (bromine water) is orange-brown. When added to an alkene such as ethene, it undergoes an addition reaction. The bromine adds across the double bond, and the orange colour disappears, forming a colourless dibromo compound.
(b)(ii) poly(ethene) ; monomers ; addition
Ethene molecules can join together in a polymerisation reaction to form poly(ethene) (also called polythene). The small ethene molecules are the monomers. Since this polymerisation involves the opening of the double bond and joining without loss of any small molecule, it is an example of addition polymerisation.
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.3 — Fuels (Part (a), (b))
• Topic C11.1 — Formulas and terminology (Part (c)(i), (c)(ii), (c)(iii), (c)(iv))
• Topic C11.4 — Alkanes (Part (c)(v))
• Topic C12.4 — Separation and purification (Part (b)(i), (b)(ii))
▶️ Answer/Explanation
(a)(i) Coal
Coal is a fossil fuel formed from the remains of ancient plants. Along with natural gas and petroleum, it is one of the three main fossil fuels.
(a)(ii) Methane
Natural gas is primarily composed of methane (CH₄), which makes up about 70–90% of its volume.
(b)(i) Fractional distillation
Fractional distillation is the process used to separate petroleum into different fractions based on their boiling points.
(b)(ii) No new substances are made / It is a separation process.
Fractional distillation is a physical change because it only separates the components of petroleum based on their boiling points. No chemical bonds are broken or formed, and no new compounds are created.
(b)(iii) Road surfaces / making roads
Bitumen is the thickest fraction obtained from petroleum distillation and is commonly used for surfacing roads and making roofing materials.
(c)(i) Octane is a hydrocarbon because it contains carbon and hydrogen atoms only.
Hydrocarbons are compounds that consist entirely of carbon and hydrogen atoms. Octane’s structure shows only carbon and hydrogen atoms bonded together.
(c)(ii) C₈H₁₈
Octane has 8 carbon atoms and 18 hydrogen atoms. The general formula for alkanes is CₙH₂ₙ₊₂, so for n=8, the formula is C₈H₁₈.
(c)(iii) Covalent bonding
Octane contains covalent bonds between its carbon and hydrogen atoms. These bonds are formed by sharing pairs of electrons between non-metal atoms.
(c)(iv) Octane contains only C–C single bonds / does not contain a C=C double bond.
Saturated hydrocarbons contain only single bonds between carbon atoms. Octane has all single bonds, making it saturated. Alkanes are saturated hydrocarbons.
(c)(v) carbon dioxide and water
Complete combustion of any hydrocarbon in excess oxygen produces carbon dioxide (CO₂) and water (H₂O) as the only products.