NZIC 2015 Assessment Schedule for Chemistry 3.5 AS 91391: DEMONSTRATE UNDERSTANDING OF THE PROPERTIES OF SELECTED GANIC COMPOUNDS Question Evidence Achieved Merit Excellence 1(a) (2)-methylpropanoyl chloride TWO correct Names and / or structure. (b) (i) (c) 3-chlorobutanal Constitutional isomers have the same molecular formula (same number of each type of atom) but the atoms have a different order of attachment. There a number of ketone and aldehyde isomers with the formula C 4 H 7 OCl that will be a correct answer. Position of Cl and carbonyl group can change and aldehydes can include a branched carbon chain. Two examples are: CH C CH CH 2 CH Cl O Cl O Definition correct Isomer correct ONE isomer drawn correctly with 3D arrangements of groups around asymmetric carbon. Correct 3D arrangements drawn, representing molecules that are enantiomers. ALL steps in the correct order. (d) 2-W 3-U 4-S 5-V 7-T (e) Aldehydes react with Tollens reagent and ketones don t. The reaction is redox, Ag + reduced to Ag (silver mirror) and aldehydes oxidised to carboxylic acids. Ketones are not able to be oxidised. With NaBH 4 both aldehydes and ketones are reduced to alcohols but aldehydes will produce a primary alcohol (functional group is on the end of the chain) and ketones will produce a secondary alcohol. FOUR out of FIVE letters in correct order ONE oxidation or reduction reaction recognised Recognises redox reactions of either aldehydes or ketones with either Tollens or NaBH 4 Aldehydes or ketones with both NaBH 4 and Tollens Compares the similarities and differences of both aldehydes and ketones with both Tollens and NaBH 4 1a 2a 3a 4a 3m 4m 1e one part well explained or both part partially explained 1e both parts comprehensively explained
Question Evidence Achieved Merit Excellence 2(a) Diol and diacid (i) (iii) In the reation, the diol and diacid (or acid chloride), water (or HCl) molecules are repeatedly removed/eliminated. Since there are functional groups at both ends of the reacting molecules a long chain molecule of repeating units known as a polymer is formed. Both acidic and basic hydrolysis of Mylar produce the same alcohol (ethan-1,2-diol). In contrast, acidic hydrolysis requires H 2 O / H + or HCl(aq) and produces the diacid, whereas basic hydrolysis requires H 2 O / OH or NaOH(aq) and produces the carboxylate ion/salt. or Defines condensation or polymerisation. One correct structure. Two products linked to the type of hydrolysis products of one reaction correctly linked to the type of hydrolysis and reagent or conditions. Compares and contrasts hydrolysis of polymer to give salt / acid and diol. Reagents with conditions and structures correct. (b) (i) Secondary alcohol oxidised to a ketone with K 2 CrO 7 /H + and ketones do not react with blue litmus. CHCHCH * CH3 C 3 CH + CHCH CH 2 major minor OH (I and III have chiral carbons (so rotate polarised light) but for 1 the two elimination products (both major and minor as drawn) have no cis-trans isomerism) One secondary alcohol structure drawn Either indicates a chiral carbon recognises elimination products 2 All 3 possible isomers drawn One isomer selected and linked to elimination products All 3 isomers recognised AND correct isomer chosen with correct structures for elimination products
1a 2a 3a 4a 2m 3m 2e with minor error or omission, 2e 3
Q Evidence Achieved Merit Excellence 3 (a) Reagent 1: Cr 2 O 2-- 7 /H + or MnO 4 (/H + ) Reagent 2: SOCl 2 /PCl 3 /PCl 5 Reagent 3: SOCl 2 /PCl 3 /PCl 5 Reagent 4: NH 3 (alc) TWO reagents TWO products correct Product 1: COOH Product 2: COCl Product 3: CH 2 Cl Product 4: CH 2 NH 2 One conversion correct, with reagents and conditions, products of the first step for both branches correct All steps and products correct (b)(i) (c) Alternatively: Reagent 1: SOCl 2 /PCl 3 /PCl 5 Reagent 2: NH 3 (alc) Reagent 3: Cr 2 O 7 2-- /H + or MnO 4 (/H + ) Reagent 4: SOCl 2 /PCl 3 /PCl 5 Product 1: CH 2 Cl Product 2: CH 2 NH 2 Product 3: COOH Product 4: COCl Use red litmus paper. Butanamine is a base so will turn red litmus blue. Butanamide will not react with red litmus. Add a drop of water to each of the solutions. With butanoic acid no reaction will be observed, as butanoic acid will dissociate slowly in water. The resulting solution will turn blue litmus red. With butanoyl chloride, a vigorous reaction will be observed as acyl chlorides are very reactive. A substitution reaction occur with water, forming butanoic acid and hydrochloric acid which is observed as white misty fumes which turn damp blue litmus paper red. Add a sample of each liquid in turn to 1 ml of water and shake. Only one liquid, butanoic acid, will readily dissolve in the water (it can form H-bonds with the mater molecules). The other two liquids will form two layers with water. Careful heating of the remaining liquids will see one more easily vaporised than the other. Cyclohexane is non-polar so would be expected to have a lower boiling point than the polar pentan-3-one molecules so will vaporise/boil at a lower temperature. ONE correct reagent. Correct observation for ONE compound. Correct solubility observation for ONE compound. Correct boiling point observation for ONE compound. Identifies both chemical tests and distinguishes between one pair of compounds. Two correct observations of solubility or boiling point linked to structures of the molecules. BOTH pairs of compounds distinguished with reagents, conditions and observations linked to species and type of reaction. Correct observations for all three species in solubility and boiling point comparison linked to the structures of the molecules a workable sequence 4
1a 2a 3a 4a 2m 3m 2e 3e Cut Scores Not Achieved Achievement Achievement with Merit Achievement with Excellence Score range 0 7 8 13 14 18 19 24 5