Carbon and silicon are elements in Group 14.
- (a)(i)Describe the lattice structure of solid C60.[2]
- (a)(ii)C60 sublimes (turns directly from solid to gas) at about 800 K. Diamond also sublimes but only above 3800 K. Explain why C60 and diamond sublime at such different temperatures.[4]
- (b)(i)State what is meant by the term hydrocarbon.[1]
- (b)(ii)Describe a test to indicate the presence of double bonds between carbon atoms in C60H18. Give the result of the test.[2]
- (c)(i)Name the type of reaction that occurred.[1]
- (c)(ii)Calculate the amount, in moles, of C60 that reacted. amount of C60 = .............................................. mol[1]
- (c)(iii)Calculate the amount, in moles, of hydrogen gas that reacted with the C60. amount of hydrogen gas = .............................................. mol[2]
- (c)(iv)Use your answers from (ii) and (iii) to deduce the molecular formula of the hydrocarbon, C60H2x. If you were unable to calculate the amount of hydrogen gas, assume that 0.00240 mol of hydrogen gas reacted. This is not the correct value for the amount of hydrogen gas that reacted. molecular formula = ..............................................[2]
- (d)(i)State the type of bonding and structure shown by silicon.[2]
- (d)(ii)When silicon reacts with magnesium, Mg2Si forms. Mg2Si is thought to contain the Si⁴⁻ ion. State the full electronic configuration of the Si⁴⁻ ion. 1s².[1]
- (d)(iii)Solid Mg2Si reacts with dilute hydrochloric acid to form gaseous SiH4 and a solution of magnesium chloride. Write an equation to show the reaction of solid Mg2Si with dilute hydrochloric acid. Include state symbols.[2]
- (d)(iv)Predict the shape of the SiH4 molecule.[1]
- (d)(v)SiH4 reacts spontaneously with oxygen to produce a white solid and a colourless liquid that turns anhydrous copper(II) sulfate blue. No other products are formed. Write an equation for the reaction of SiH4 with oxygen. State symbols are not required.[1]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.
- [2] simple molecular
- regular arrangement (of C60 molecules)
- [4] C60 has (weak) intermolecular / VdW / London / dispersion / id-id forces (and covalent bonds)
- diamond has covalent bonds
- (diamond's) bonds are stronger
- more energy required / lots of energy to break (covalent bonds in diamond)
- [1] (a molecule / compound that is made up of)
- carbon and hydrogen (atoms) only
- [2] add bromine (water) / Br2(aq)
- (brown to) colourless / decolourised
- [1] addition
- [1] (nc60 = 0.144 / 720 =) 2 × 10⁻⁴
- [2] PV = nRT
- Δn = (p1 - p2)V / RT
- Δn = (1.00 × 10⁵ – 2.21 × 10⁴).100 × 10⁻⁶ / 8.31 × 293
- = 0.00320
- [2] (C60:H2 =) 2.00 × 10⁻⁴ : 0.00320 or 1:16
- C60H32
- [2] giant (molecular)
- (each Si has four) covalent (bonds)
- [1] 1s² 2s² 2p⁶ 3s² 3p⁶
- [2] Mg2Si(s) + 4HCl(aq) → SiH4(g) + 2MgCl2(aq)
- species AND balancing
- state symbols
- [1] tetrahedral
- [1] SiH4 + 2O2 → SiO2 + 2H2O
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