TOPIC 13 ANSWERS & MARK SCHEMES QUESTIONSHEET 1 ALKANES

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1 QUESTIONSHEET 1 ALKANES a) (i) UV light / temperatures > 500 ºC (ii) CH 4 (g) + Cl 2 (g) Cl(g) + HCl(g) Cl(g) + Cl 2 (g) Cl 2 (l) + HCl(g) Cl 2 (l) + Cl 2 (g) CHCl 3 (l) + HCl(g) CHCl 3 (l) + Cl 2 (g) CCl 4 (l) + HCl(g) (State symbols are not essential.) (iii) Chloromethanes are as readily attacked by chlorine as methane itself Therefore, as they accumulate, they become chlorinated (iv) Fractional distillation (v) Use a limited amount of chlorine / excess of methane (vi) Use excess of chlorine b) Reason Isomerism (i) Cl Cl (½) 1, 2 Dichloroethane (½) CHCl 2 (½) 1,1 Dichloroethane (½) (ii) (iii) CHCl 2 Cl (½) 1,1,2 Trichloroethane (½) CCl 3 (½) 1,1,1 Trichloroethane (½) CHCl 2 CHCl 2 (½) 1,1,2,2, - Tetrachloroethane (½) CCl 3 Cl (½) 1,1,1,2 Tetrachloroethane (½) (Names must be correctly related to formulae to qualify for marks.) Quality of Language: the correct use of at least 3 technical terms such as: excess, isomerism (isomers), limited, fractional distillation, substituted.

2 QUESTIONSHEET 2 ALKENES a) 2C 3 H 6 + 9O 2 6CO 2 + 6H 2 O b) (i) Hydrogen and a nickel catalyst at 150ºC (ii) Bromine CH3 CH C CH Br Br (iii) Hydrogen bromide (show both isomers produced) CH C Br H C Br (2) c) (i) C 2 H 4 O C 2 H 5 OH (ii) CH OH CH CH OH

3 QUESTIONSHEET 3 SUBSTITUTION REACTIONS OF HALOALKANES a) (i) 1-bromopropane Br (ii) 2-bromobutane CHBr (iii) 2-bromo-2-methylpropane ( ) 3 CBr b) (i) Aqueous NaOH / KOH Heat / boil under reflux (ii) KCN Conditions Boil under reflux (not just reflux ) with KCN in alcoholic solution / aqueous alcohol Equation Br + KCN CN + KBr Name Butanenitrile NH 3 Conditions Heat (½) in a sealed tube (½) with alcoholic NH 3 Equation Br + NH 3 NH 2 + HBr Or NH 3 + Br - Name Propylamine Or propylammonium bromide (iii) Nucleophilic substitution c) (i) C 2 H 5 Cl < C 2 H 5 Br < C 2 H 5 I (ii) Decrease in bond dissociation enthalpy from C Cl to C I

4 QUESTIONSHEET 4 HALOALKANES: SUBSTITUTION VERSUS ELIMINATION a) Name of main product Butan-2-ol Type of reaction Nucleophilic (½) subsitution (½) Equation CHBr + KOH CH(OH) + KBr b) Names and formulae But-1-ene =CH and but-2-ene CH=CH Type of reaction Elimination Equation CHBr + KOH =CH / CH=CH + KBr O c) Boil / heat (in contrast to warm ) with concentrated alcoholic / ethanolic KOH d) NaOH / Ca(OH) 2 / Na 2 CO 3 / Ag 2 O e) Elimination has a relatively high activation energy and cannot occur at all at room temperature

5 QUESTIONSHEET 5 OXIDATION OF ALCOHOLS a) Primary alcohol(s) B (½) butan-1-ol (½) D (½) 2-methylpropan-1-ol (½) Secondary alcohol(s) A (½) butan-2-ol (½) Tertiary alcohol(s) C (½) 2-methylpropan-2-ol (½) Allow marks for names even if classification is wrong. b) (i) Propan-1-ol is oxidised via propanal to propanoic acid (ii) Propan-2-ol is oxidised to propanone (iii) Butan-1-ol is oxidised to butanal which distils out as formed (iv) 2-Methylpropan-2-ol is a tertiary alcohol and resists oxidation (v) Why Na 2 Cr 2 O 7 is added to butan-1-ol To ensure that the oxidising agent is never present in excess Why the product can be distilled out Aldehydes / butanal have a low boiling point compared with related alcohols / butan-1-ol

6 QUESTIONSHEET 6 OTHER REACTIONS OF ALCOHOLS a) (i) OH = O (ii) ºC (iii) Elimination (of water) / dehydration (iv) Catalyst / dehydrating agent (v) Oxidation of the alcohol (vi) Al 2 O 3 / pumice / kaolin b) (i) Add PCl 5 at room temperature Or PCl 3 and boil under reflux Then distil off 1-chlorobutane (ii) Add NaBr / KBr and concentrated H 2 / H 3 PO 4 Or concentrated hydrobromic acid Or red phosphorus and bromine Heat / boil under reflux Then distil off 1- bromobutane (iii) Add methanoic acid and a little concentrated H 2 Heat / boil under reflux Then distil off butyl methanoate Accept HCl(g) dissolved in butan-1-ol instead of conc. H 2 c) (i) OH + PCl 5 Cl + POCl 3 + HCl Or 3 OH + PCl 3 3 Cl + H 3 PO 3 (ii) OH + NaBr Br + NaH O Or OH + HBr Br O Or 3 OH + PBr 3 3 Br + H 3 PO 3 (iii) HCOOH + OH ž HCOO O

7 QUESTIONSHEET 7 TEST QUESTION I a) Compound Structural formula IUPAC name A B C D E F G OH CHO CH = CH(OSO 2 OH) CHBr CH(OH) CO Propan-1-ol Propanal Propene Isopropyl hydrogen sulfate * 2-Bromopropane Propan-2-ol Propanone * Or 1-Methylethyl hydrogen sulfate. Award for each correct formula and for each name. b) B is an aldehyde (½) G is a ketone (½) Aldehydes are oxidised by Tollens reagent which becomes reduced to silver Ketones are resistant to oxidation

8 QUESTIONSHEET 8 TEST QUESTION II a) (i) Reagent Bromine water / other bromine solution Observation Br 2 is decolourised / changes colour from red to colourless Equation ( ) 3 CH = + Br 2 ( ) 3 CHBr Br (ii) Reagent Phosphorus pentachloride / PCl 5 Observation Misty white fumes Equation OH + PCl 5 Cl + POCl 3 + HCl Or Reagent Ethanoic acid and conc. sulfuric acid (and heat) Observation Smell of pear drops Equation COOH + OH COO O (iii) Reagents Both the above Observation Br 2 (aq) remains brown / red (½) No fumes with PCl 5 (½) Equation No reactions b) (i) To liberate halide ions from covalent halides (ii) To avoid precipitating silver oxide (iii) From 1-chloropropane From 1-bromopropane From 1-iodopropane White precipitate (½) of AgCl (½) Off-white / cream precipitate (½) of AgBr (½) Yellow precipitate (½) of AgI (½) (iv) White precipitate / AgCl is readily soluble in dilute aqueous ammonia Cream precipitate / AgBr is soluble only in concentrated aqueous ammonia Yellow precipitate / AgI is insoluble in both dilute and concentrated aqueous ammonia

9 QUESTIONSHEET 9 TEST QUESTION III a) n (alkene) = 224/22400 = 0.01 mol n (Br 2 ) = 3.20/160 = 0.02 mol 1 mol alkene 2 mol Br 2 ; hence 2 C = C bonds b) (i) Compound Structural formula IUPAC name X Y Z BrCH = CH Br Br Br OH OH 1,4-Dibromobut-2-ene 1,4-Dibromobutane Butane-1,4-diol (Award for each correct formula and for each name.) (ii) Step A Reagent Hydrogen Conditions Nickel catalyst Heat Or Platinum catalyst Room temperature Step B Reagent Aqueous NaOH / KOH Conditions Heat / boil under reflux Step C Reagents Na 2 Cr 2 O 7 (aq) / K 2 Cr 2 O 7 (aq) and dilute H 2 Conditions Heat / boil under reflux c) = CH CH = (Allow = C = CH )

10 QUESTIONSHEET 10 TEST QUESTION IV a) (i) Stage 1 Reagent NaBr + conc. H 2 / conc. HBr(aq) Conditions Heat / boil under reflux Equation CH(OH) + NaBr CHBr + NaH O Or CH(OH) + HBr CHBr O Stage 2 Reagent Zn + dil. H 2 / NaBH 4 / other reducing agent Conditions Boil under reflux Equation CHBr + [H] + [Br] (ii) Stage 1 Reagent Conc. H 2 Or Al 2 O 3 / pumice / kaolin Conditions C Or 350 C Equation CH(OH) CH = O Stage 2 Reagent H 2 Conditions Ni / Pt catalyst Equation CH = b) Stage 1 Reagent Br 2 * Conditions UV light Equation + Br 2 Br + HBr Stage 2 Reagent NaOH(aq) Conditions Heat / boil under reflux Equation Br + NaOH OH + NaBr *Allow Cl 2 instead of Br 2, although in practice Cl, being a gas, would be difficult to handle.

11 QUESTIONSHEET 11 TEST QUESTION V a) (i) Bromine and uv light (ii) Bromine (2) any other incorrect conditions e.g. uv light (-1) (iii) hydrogen, nickel or platinum, 150ºC - 300ºC (iv) Steam (or water), phosphoric acid, about 300ºC b) (i) H C (ii) C