Questions 1
(a)Topic -3.1 Electronegativity and bonding
(b)Topic -3.7 Dot-and-cross diagrams
(c)Topic -1.4 Ionisation energy
(d)Topic -7.2 Brønsted–Lowry theory of acids and bases
(e)Topic -7.2 Brønsted–Lowry theory of acids and bases
The Pauling electronegativity values of elements can be used to predict the chemical properties of compounds. Use the information in Table 1.1 to answer the following questions.
(a) (i) Define electronegativity.
(ii) O and S are in Group 16. Explain the difference in the Pauling electronegativity values of O and S.
(b) (i) LiH is an ionic compound. Draw a dot‑and‑cross diagram of LiH. Include all electrons.
(ii) Suggest the shape of a molecule of \(H_2S\).
(c) (i) Write an equation that represents the first ionisation energy of H.
(ii) Explain why there is no information given in Table 1.1 for the second ionisation energy of H.
(iii) Give the full electronic configuration of \(S^{2+}\)(g).
(d) \(CO_2\) and \(SO_2\) are acidic gases.
(i) Write an equation for the reaction of \(SO_2\) with \(H_2O\).
(ii) Write an equation for the reaction of \(SO_2\) with NaOH.
(iii) Construct an equation for the reaction of \(CO_2\) with \(Mg(OH)_2\).
(e) (i) Complete Table 1.2 by placing a tick (✓) to show which of the compounds have molecules with an overall dipole moment.
(ii) At 150°C and 103kPa, all of the compounds listed in Table 1.2 are gases. Under these conditions, 0.284g of one of the compounds occupies a volume of \(127cm^3\). Use this information to calculate the \(M_r\) of the compound. Hence, identify the compound from those given in Table 1.2. Show your working.
▶️Answer/Explanation
Ans:
(a)(i) power of an atom to attract electrons to itself
(ii) • O lower nuclear charge / lower proton number
• O has (one) fewer shell than S / less shielding
• greater attraction (for nucleus) in O
(ii) non-linear
(i) \(H(g) → H^+(g) + e^–\)
(ii) H (cannot undergo second ionisation because it only) has one electron / \(H^+\) has no electron
(iii) \(1s^2 2s^2 2p^6 3s^2 3p^2\)
(d)(i) \(SO_2 + H_2O → H_2SO_3\)
(ii) \(SO_2 + 2NaOH → Na_2SO_3 + H_2O\)
(iii) \(CO_2 + Mg(OH)_2 → MgCO_3 + H_2O\)
Questions 2
(a)Topic -27.1 Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
(b)Topic -27.1 Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
(c)Topic -27.1 Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
(d)Topic -7.2 Brønsted–Lowry theory of acids and bases
The Group 2 elements Mg to Ba are all silvery‑white reactive metals.
(a) (i) Draw a labelled diagram to show the bonding and structure of the Group 2 metals at room temperature.
(ii) Explain why Mg has a higher electrical conductivity than Na.
(b) Write an equation for the reaction of magnesium with cold water.
(c) Identify a single reagent that can be used to distinguish separate samples of dilute \(Mg(NO_3)_2(aq)\) and dilute \(Ba(NO_3)_2(aq)\). Explain your answer.
(d) (i) Describe what is observed when \(SrI_2(aq)\) reacts with concentrated sulfuric acid.
(ii) Compound X, an anhydrous Group 2 bromide, is dissolved in water and titrated against aqueous silver nitrate. A solution containing 0.250g of X requires \(33.65cm^3\) of \(0.0500moldm^{–3}\) \(AgNO_3(aq)\) for complete reaction. Identify X. Show your working.
▶️Answer/Explanation
Ans:
(ii) Mg has more delocalised \(e^–\) (than Na)
(b) \(Mg + 2H_2O → Mg(OH)_2 + H_2\)
(c) reagent = any named/formula of soluble sulfate OR H₂SO₄
OR any named/formula of soluble hydroxide
BaSO₄ insoluble (& MgSO₄ soluble)
OR (Ba(OH)₂ soluble &) Mg(OH)₂ insoluble
(d)(i) white precipitate
yellow solid effervescence / misty fumes
(dark) grey solid / purple gas rotten egg smell
(ii) moles of AgNO₃ =\(\frac{33.65}{1000}\times 0.0500 (= 1.68(25) \times 10^{–3}\))
moles of X = ½ × moles of AgNO₃ = 0.250 ÷ \(M_r\)(X) ∴ \(M_r\)(X) = 297.2 1
Ar of Group 2 element is 297.2 – 2(79.9) = 137.4 AND X is BaBr₂.
Questions 3
(a)Topic -14.2 Alkenes
(b)Topic -17.1 Aldehydes and ketones
(c)Topic -14.1 Alkanes
(d)Topic -5.1 Enthalpy change, ΔH
Alkenes undergo an addition reaction with a 1:1 mixture of CO and H₂ to form aldehydes. Fig. 3.1 shows the reaction of propene with a 1:1 mixture of CO and H₂.
(a) (i) Define addition reaction.
(ii) Aldehydes A and B are structural isomers. State the type of structural isomerism shown by A and B.
(iii) Name A.
(iv) The complete reaction of propene with a 1:1 mixture of CO and H₂ produces A and B only. The product mixture contains 96% A and 4% B. Calculate the mass of A produced in this reaction when \(5.00×10^3 kg\) of propene is used.
(b) A and B show reactions typical of aliphatic aldehydes.
(i) A undergoes a nucleophilic addition reaction with a mixture of HCN and KCN, forming compound C. Complete the diagram to show the mechanism for this reaction. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. Draw the structure of the organic intermediate.
(ii) Table 3.1 shows information about three experiments involving B. Complete Table 3.1. 
(iii) B, C₄H₈O, is oxidised by acidified potassium manganate(VII). Complete the equation for this reaction. Use [O] to represent one atom of oxygen from the oxidising agent.
(iv) C is a chiral molecule. Circle any chiral centres in the structure of C shown in Fig. 3.2.
(c) When propene reacts with CO and an excess of H₂, an alkane and a mixture of alcohols are formed instead. The alcohols are isomers of each other. Suggest the molecular formulae of the alkane and the alcohols that are formed under these conditions.
molecular formula of alkane ………………………………………………………………………………………..
molecular formula of alcohols ………………………………………………………………………………………
(d) The reaction of ethene, C₂H₄, with a 1:1 mixture of CO and H₂ is shown in equation 1.
equation 1 C₂H₄(g) + CO(g) + H₂(g) \(\rightleftharpoons \) CH₃CH₂CHO(g)
At atmospheric pressure a cobalt‑based catalyst is used in this reaction.
(i) State and explain the effect of using a catalyst on this reaction.
(ii) Explain why the yield of CH₃CH₂CHO(g) increases when the overall pressure of the reaction mixture is increased.
(iii) Use the information in Table 3.2 to calculate the enthalpy change, \(ΔH_r\), of the reaction in equation 1.
equation 1 C₂H₄(g) + CO(g) + H₂(g) \(\rightleftharpoons \) CH₃CH₂CHO(g)
(iv) The reaction mixture is cooled to collect CH₃CH₂CHO as a liquid. Identify all types of van der Waals’ forces that are present between molecules of CH₃CH₂CHO.
▶️Answer/Explanation
Ans:
(a)(i) (a reaction where) two (or more) compounds / reagents / molecules form (only) one product
(ii) position(al isomerism)
(iii) butanal
(iv) 96% × (5000 / 42.0) × 72.0 = 8230 or 8229 (kg)
(ii) acidified K₂Cr₂O₇
Tollens’ reagent
no reaction
(iii) C₄H₈O + [O] → C₄H₈O₂
(c) alkane C₃H₈
alcohols C₄H₁₀O
(d)(i) increases the rate of reaction
by providing an alternative reaction pathway of lower \(E_a\)
(ii) equilibrium moves to right/products where fewer moles / smaller amount of gas
(iii) –187 –(–111) –(+52)
= –128 (kJ mol–1)
(iv) instantaneous dipole—induced dipole / id—id
AND permanent dipole—permanent dipole / pd—pd
Questions 4
(a)Topic -14.1 Alkanes
(b)Topic -13.2 Characteristic organic reactions
(c)Topic -13.2 Characteristic organic reactions
(d)Topic -22.1 Infrared spectroscopy
Fig. 4.1 shows some reactions of compound D, 2‑bromobutane.
(a) (i) State the reagent and conditions used to form E in reaction 1.
(ii) Draw the structure of one repeat unit of the addition polymer that forms from E.
(iii) E also forms when F is heated strongly in the presence of an Al₂O₃ catalyst. Write an equation for this reaction.
(b) (i) Predict what is observed in reaction 2.
(ii) Identify the yellow precipitate and the organic ion formed in reaction 3.
yellow precipitate …………………………………………………………………………………………………
organic ion ………………………………………………………………………………………………………….
(c) (i) State the type of reaction that occurs in reaction 4.
(ii) Reaction 5 is similar to the reaction of LiAlH₄ with carboxylic acids to form alcohols. Suggest the role of LiAlH₄ in reaction 5.
(d) (i) Fig. 4.2 shows the infrared spectrum of one of the compounds D, E, F, G or H.
Use information from Table 4.1 (on page 14) to identify which of the compounds D, E, F, G or H produces the infrared spectrum in Fig. 4.2. Explain your answer.
(ii) In the mass spectrum of D, the relative abundance of the molecular ion peak is 3.4. Predict the relative abundance of the M+2 peak for D. Explain your answer.
▶️Answer/Explanation
Ans:
(a)(i) NaOH in alcohol / ethanol AND heat (under reflux)
(iii) C₄H₁₀O / CH₃CH(OH)C₂H₅ → C₄H₈ / CH₃CHCHCH₃ + H₂O
(b)(i) cream(-coloured) / off-white precipitate (forms)
(ii) \(CHI_3\) / iodoform / tr(i)iodomethane
\(CH_3CH_2CO_2^–\)/ propanoate
(c)(i) substitution
(ii) reducing agent
(d)(i) G
(absorption at) 2200–2250 \((cm^{–1})\) AND C≡N 1
(ii) 3.4 AND relative abundance of \(^{79}Br:^{81}Br\) ≅ 50:50 OR 1:1