Questions 1
Topic – 12.1 Nitrogen and sulfur
(a) (i) Explain the lack of reactivity of nitrogen gas, N₂(g).
(ii) Covalent bonds can be σ bonds or π bonds. Complete Table 1.1 to show the number of σ and π bonds in a molecule of N₂ and to describe how the orbitals overlap to form σ and π bonds
(b) (i) A sample of Al reacts with an excess of Cl₂. State the oxidation number of Al in the product of the reaction.
oxidation number of Al ……………………………………………..
(ii) State what determines the maximum oxidation number of the Period 3 elements in their oxides.
(c) Separate samples of aluminium oxide, Al₂O₃, and phosphorus(V) oxide, P₄O₁₀, react with an excess of NaOH(aq) at room temperature.
(i) Give the state of Al₂O₃ and P₄O₁₀ at room temperature.
(ii) Write an equation for the reaction of each oxide with an excess of NaOH(aq) at room temperature.
Al₂O₃ + …………………………………………………………………………………………………………….
P₄O₁₀ + ……………………………………………………………………………………………………………
(d) The oxide of silicon reacts with calcium oxide in an addition reaction to produce calcium silicate, CaSiO₃. The oxidation number of calcium in CaSiO₃ is +II.
(i) Deduce the oxidation number of silicon in calcium silicate.
(ii) Calcium oxide can be made from calcium carbonate in a single-step reaction. Identify the type of reaction that occurs.
▶️Answer/Explanation
Ans:
(a)(i) M1 (N₂ molecules /molecule(s) of N₂) have a strong triple (covalent) bond
M2 (N₂ molecules /molecule(s) of N₂) are non-polar
(b)(i) (+)III
(ii) number of outer / valence electrons
(c)(i) both states shown as solid
(ii) M1 correctly balanced equation for aluminium oxide
Al₂O₃ + 2NaOH + 3H₂O → 2NaAl(OH)₄
M2 correctly balanced equation for P4O10 and an excess of NaOH
\(P_4O_{10} + 12NaOH→ 4Na_3PO_4 + 6H_2O\)
(d)(i) (+)IV
(ii) thermal decomposition
Questions 2
Topic – 7.1 Chemical equilibria: reversible reactions, dynamic equilibrium
\(N_2(g)\) reacts with \(H_2(g)\) in the Haber process, as shown in reaction 1.
Table 2.1 shows the different conditions used to produce three equilibrium mixtures, A, B and C. 
(a) Describe and explain the change, if any, to the percentage yield of NH₃(g) produced in B compared to A.
(b) (i) Describe and explain the change, if any, to the percentage yield of NH₃(g) produced in C compared to A.
(ii) Describe and explain the change to the rate of the forward reaction that occurs to establish the equilibrium in C compared to A. You do not need to refer to the Boltzmann distribution in your answer.
(c) (i) Write an expression for the equilibrium constant, \(K_p\), for reaction 1. State the units.
(ii) Equilibrium mixture D is made when 1.0mol of \(N_2(g)\) and 3.0mol of \(H_2(g)\) are added to a sealed container at 750°C and 1000 atm and left to reach equilibrium. This mixture contains 1.16mol of NH₃(g). Calculate the mole fraction of NH₃(g) in D.
(iii) The mole fraction of \(N_2(g)\) is 0.625 in a new equilibrium mixture, E. Calculate the partial pressure of \(N_2(g)\) in E when the total pressure is 1000 atm.
(d) When oxides of nitrogen escape into the atmosphere they may be involved in:
• formation of acid rain from sulfur dioxide
• formation of photochemical smog.
(i) Identify the role of NO and \(NO_2\) in the formation of \(H_2SO_4\) from \(SO_2\) in the atmosphere to produce acid rain. Use relevant equations to support your answer.
(ii) Outline how NO and \(NO_2\) may contribute to the formation of photochemical smog.
▶️Answer/Explanation
Ans:
(a) 58% / no change / stays the same AND catalysts don’t affect yield / iron is a catalyst
(b)(i) less yield (in C than A) AND (as) exothermic (forward reaction)
(ii) (increase in temperature / energy from A to C (so))
M1 more collisions with particles that have \(E>E_a\) AND increase frequency of effective collisions
M2 (initial) rate (of the forward reaction) increases
(c)(i) M1 \(K_p = (pNH_3)^2 / (pN_2)(pH_2)^3\)
M2 \(atm^{–2}\)
(ii) M1 correct amount \(N_2\) at equilibrium = 1 – 1.16 / 2 = 0.42
AND correct amount \(H_2\) at equilibrium = 3.0 – (1.16 × 3 / 2) = 1.26
M2 express amount of ammonia as a mol fraction in terms of total amount of \(N_2 + H_2 + NH_3\) at equilibrium = 1.16 / \((N_2 + H_2 +1.16)\) = 0.408 OR 0.41
(iii) 0.625 × 1000 = 625 (atm)
(d)(i) M1 catalyst
M2 2 equations to show the catalytic activity of \(NO_2\) in formation of \(SO_3\) from \(SO_2\)
SO₂ + NO₂ → NO + SO₃
2NO + O₂ → 2NO₂
M3 describe production of \(H_2SO_4\) from \(SO_3\) and water (can be shown in an equation).
SO₃ then reacts with (rain)water / moisture / water vapour to make sulfuric acid / \(H_2SO_4\) OR \(SO_3 + H_2O→ H_2SO_4\)
(ii) M1 unburned hydrocarbons combine with NO and /\( NO_2\)
M2 to form PAN / peroxyac(et)yl nitrate
Questions 3
Topic – 23.4 Gibbs free energy change, ΔG
(a) Write an equation to show the reaction for the standard enthalpy change of formation of \(H_2O\). Include state symbols.
(b) Water is one of the products in the reaction of \(B_2O_3\) and \(NH_3\), as shown in reaction 2.
reaction 2 \(B_2O_3 + 2NH_3 → 2 BN + 3H_2O\)
Table 3.1 shows information about the standard enthalpy change of formation, \(ΔH _f^{\theta}\), of some substances.
Calculate the enthalpy change, ∆H, for reaction 2 using the data from Table 3.1.
(c) Boron carbide is a hard crystalline solid that has a melting point greater than 2000°C.
(i) Suggest the structure and bonding in boron carbide.
(ii) 100g of pure boron carbide contains 78.26g of boron. Calculate the empirical formula of boron carbide. Show your working.
▶️Answer/Explanation
Ans:
(a) \(H_2 (g) + ½O_2 (g)→ H_2O(l)\)
M1 correct equation only
M2 correct state symbols based on this equation
(b) ∆H = –(–1264) – (2 × –46) + (2 × –134) + (3 × –286) = (+)230 \(kJ mol^{–1}\)
M1 correct expression in terms of all 4 enthalpy changes of formation AND correct stoichiometry (as described in given equation)
M2 correct calculation based on figures given
(c)(i) giant (molecular and) covalent
(ii) M1 gives the correct expression or calculates mol B compared to mol C
78.26 / 10.8 (= 7.246 / 7.25 mol B) AND 21.74 / 12 (=1.81(2) mol C)
M2 Find B : C ratio AND use this to state empirical formula
7.246 to 7.25 / 1.817 to 1.82 = 3.99 to 3.98 mol B : 1 mol C
(so) \(B_4C\) OR \(CB_4\)
Questions 4
Topic – 15.1 Halogenoalkanes
(a) NH₃(g) reacts with HCl (g) to produce NH₄Cl(s), as shown.
NH₃(g) + HCl → NH₄Cl(s)
Draw a diagram to show the ionic, covalent and coordinate bonding present in a formula unit of NH₄Cl(s) .
(b) An exothermic reaction occurs when NH₄⁺(aq) is added to OH⁻(aq).
(i) Identify the type of reaction.
(ii) Construct an ionic equation for the reaction of NH₄⁺ and OH⁻.
(c) Substitution reactions of NH₃ and OH⁻ with halogenoalkanes both involve a lone pair of electrons.
(i) Name the role of NH₃ and OH⁻ in these reactions.
(ii) Suggest which species, NH₃ or OH⁻, is more reactive during these reactions. Explain your answer.
(d) When 2-bromo-2-methylpropane reacts with OH⁻, two mechanisms, \(S_N1\) and \(S_N2\), both occur. The \(S_N2\) mechanism has a slower rate. Fig. 4.1 shows the reaction pathway diagram for the \(S_N1\) mechanism. Sketch a graph on Fig. 4.1 to show the reaction pathway for the \(S_N2\) mechanism.
(e) (i) Complete Fig. 4.2 to show the mechanism for the \(S_N1\) reaction that occurs when CH₃CHBrC₂H₅ reacts with NH₃ to produce CH₃CH(NH₂)C₂H₅. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate 
(ii) Identify the inorganic product that forms in the reaction in Fig. 4.2.
(iii) Give the systematic name for the organic product CH₃CH(NH₂)C₂H₅.
(f) (i) Complete Table 4.1 by drawing the structural formula of the intermediate that is formed when 2-bromo-2-methylpropane reacts in an \(S_N1\) reaction. 
(ii) Identify the halogenoalkane in Table 4.1 that has the greater tendency to react using the \(S_N1\) mechanism. Explain your answer.
▶️Answer/Explanation
Ans:
1(a)
Correct representation or label showing
M1 (ionic bond between) NH₄⁺ and \(Cl^–\) AND 4 N—H covalent bonds OR 4 shared pairs of electrons in NH₄
M2 1 N—H coordinate bond OR arrow on bond/line in correct direction or only 1 bonding pair using the same symbol for electrons 1
(b)(i) acid–base reaction
(ii) NH₄⁺ + OH⁻ → NH₃ + H₂O
(c)(i) nucleophile
(ii) OH⁻ (more reactive because) negatively charged species more attracted to halogenoalkane and / or \(C^{\delta +}\) and / or intermediate and / or \(C^+\)
OR NH₃ (more reactive because) N electrons less tightly held
OR N is more able to donate (lp) electrons (to make the covalent bond)
OR N is less electronegative
ORA
(d)
(e)(i)M1 dipole and correct arrow on C—Br of 2-bromobutane
M2 lone pair on \(NH_3\) attacking C(+) of the intermediate drawn
M3 curly arrow showing bond between N—H breaking and pointing towards the N
(ii) NH₄Br / ammonium bromide
(iii) butan-2-amine OR butyl-2-amine
(f)(i)
(ii) M1 2-bromo-2-methylpropane AND more stable carbocation / \(C^+\)
M2 alkyl groups have an inductive effect (of alkyl groups)
AND 2-bromo-2-methylpropane has more / most alkyl groups attached (to \(C^+\)) / carbocation contains more alkyl groups
Questions 5
Topic – 14.1 Alkanes
(a) M reacts to form R by the addition of one reagent, as shown in Fig. 5.1.
Identify the reagent and conditions for this reaction.
(b) R is also made from M by two steps, as shown in Fig. 5.2. 
(i) Identify the reagents and conditions for steps 1 and 2 in Fig. 5.2.
step 1 ………………………………………………………………………………………………………………..
step 2 ………………………………………………………………………………………………………………..
(ii) Name the mechanism for step 1 in Fig. 5.2.
(c) The infrared spectrum of R is shown in Fig. 5.3.
Use the absorptions in the region above \(1500cm^{–1}\) in Table 5.1 when answering this question.
• Add F to Fig. 5.3 to identify the peak that is present in an infrared spectrum of both Q and R. Identify the bond that corresponds to the absorption for F.
………………………………………………………………………………………………………………………….
• Add G to Fig. 5.3 to identify the peak that is not present in an infrared spectrum of Q. Identify the bond that corresponds to the absorption for G.
(d) Y is made from Q in a three-step reaction.
(i) Draw the structure of W in the box in Fig. 5.4. [1]
(ii) In step 2, W is heated with HCl (aq) to produce X and an inorganic product. Identify the formula of the inorganic product.
(iii) In step 3, X reacts with reducing agent Z to produce Y. Complete the equation for the reaction of X with Z. Use a molecular formula to represent the organic product. Use [H] to represent one atom of hydrogen from Z.
…… \(C_8H_{12}O_4 + ……[H]\) …………………………………………………………………………..
(iv) Identify Z
▶️Answer/Explanation
Ans:
(a) cold dilute \(KMnO_4\) OR cold dilute potassium manganate(VII)
(b)(i) step 1 …..\(Br_2\) (in the dark)
step 2 …..NaOH(aq) + heat
(ii) electrophilic addition
(d)(i)W =
(ii) NH₄Cl
(iii) \(C_8H_{12}O_4 + 8[H] → C_8H_{16}O_2 + 2H_2O\)
(iv) LiAlH₄