CIE iGCSE Co-Ordinated Science C11.1 Formulas and terminology Exam Style Questions Paper 4
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.1 — Formulas and terminology / Hydrocarbons (Part (a))
• Topic C11.3 — Fuels / Natural gas (Part (b))
• Topic C11.2 — Naming organic compounds (Part (c))
• Topic C11.7 — Polymers / Addition polymerisation (Part (d)(i) & (d)(ii))
• Topic C3.1 — Formulas / Balancing equations (Part (e))
▶️ Answer/Explanation
(a) Compound C is not a hydrocarbon because it contains oxygen; hydrocarbons contain only hydrogen and carbon.
Compound C has an -OH group (alcohol functional group), meaning it contains oxygen atoms in addition to carbon and hydrogen, so it is not a hydrocarbon.
(b) Natural gas
Compound D is methane (CH₄), which is the main constituent of natural gas, a fossil fuel formed from ancient organic matter.
(c) Propane
Compound B has the formula C₃H₈, which is the third member of the alkane homologous series, named propane.
(d)(i) The polymer structure is –[–CH₂–CH₂–]– with single bonds between carbon atoms:
Ethene monomers (compound A with C=C bond) join by breaking the double bond and forming single bonds between carbon atoms in a long chain.
(d)(ii) Difference 1: Addition polymerisation only occurs in unsaturated monomers (with C=C bonds), while condensation polymerisation involves different types of monomers.
Difference 2: Addition polymerisation only forms the polymer molecule, whereas condensation polymerisation forms the polymer and a small molecule (like water) per linkage.
Addition polymerisation uses monomers with double bonds; condensation polymerisation joins monomers with functional groups, releasing a by-product.
(e) \( \text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O} \)
Propane combustion requires 5 molecules of oxygen to produce 3 molecules of carbon dioxide and 4 molecules of water. The equation is balanced with 3 carbon, 8 hydrogen, and 10 oxygen atoms on both sides.
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C11.1 — Formulas and terminology (Part (a))
• Topic C11.7 — Polymers (Part (b), (c))
• Topic C12.5 — Qualitative analysis (Part (d))
• Topic C2.5 — Simple molecules and covalent bonds (Part (e))
▶️ Answer/Explanation
(a)(i) Molecular formula of X = C₆H₁₆N₂
The structural formula shows 6 carbon atoms (including two in the CH₃ groups at each end and four in the chain), 16 hydrogen atoms, and 2 nitrogen atoms (in the -NH₂ groups).
(a)(ii) Molecule X is not a hydrocarbon because:
It contains nitrogen atoms in addition to carbon and hydrogen. Hydrocarbons are compounds that contain only carbon and hydrogen atoms. Molecule X contains nitrogen (N) atoms, so it is not a hydrocarbon.
(b) Structure of nylon:
Nylon is a condensation polymer formed by the reaction between a dicarboxylic acid (molecule Y, which has -COOH groups at both ends) and a diamine (molecule X, which has -NH₂ groups at both ends). The polymer chain consists of repeating units joined by amide (peptide) bonds (-CO-NH-).
(c) Two differences between condensation and addition polymerisation:
(d) Test for carbon dioxide:
Test: Bubble the gas through limewater (calcium hydroxide solution).
Positive result: The limewater turns milky/cloudy due to the formation of insoluble calcium carbonate.
(e) Properties of simple molecular compounds:
✓ Low melting point
✓ Poor electrical conductivity when solid
Simple molecular compounds have weak intermolecular forces, so they have low melting and boiling points. They do not conduct electricity because they have no free ions or electrons to carry charge.