A Level Chemistry OCR A - PAPER 2 incorrect Questions & Answers

Which compound is used as a standard for NMR chemical shift measurements? a) Si(CH₃)₄ b) CDCl₃ c) D₂O d)CCl₄ - ANSWERSa) Si(CH₃)₄ which compound doesn't react with nucleophiles? a) CH₃CH₂CHO b) CH₃CHCH₂ c) CH₃CH₂COCH₃ d)CH₃CH₂CH₂Cl - ANSWERSb) CH₃CHCH₂ which molecule is not planar? a) C₂H₄ b) C₂H₆ c) H₂CO d) HCN - ANSWERSb) C₂H₆ ethanol can be prepared by different reactions which reaction has the lowest atom economy? a) C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ b) C₂H₄ + H₂O→ C₂H₅OH c) C₂H₅Br + H₂O → C₂H₅OH + HBr d) CH₃COOC₂H₅ + H₂O → C₂H₅OH + CH₃COOH - ANSWERSc) C₂H₅Br + H₂O → C₂H₅OH + HBr The breakdown of ozone is catalysed by NO radicals which equation is a propagation step in the mechanism for this process? a) NO + O₂ → N + O₃ b) NO + O₂ → NO₂ + O c) N + O₃ → NO + O₂ d) NO₂ + O → NO + O₂ - ANSWERSd) NO₂ + O → NO + O₂ benzene reacts with an organic reagent in the presence of a halogen carrier to form phenylethanone? which - ANSWERS how many straight-chain structural isomers of C₇H₁₅Cl? a) 1 b) 2 c) 3 d) 4 - ANSWERSb) 2 which statement supports the delocalised model for the structure of benzene? 1. all carbon-carbon bonds have the same length 2. the enthalpy change of hydrogenation of benzene is less exothermic than expected 3. bromine reacts with benzene less readily than with cyclohexene - ANSWERS1 & 2 & 3 a solid organic compound can be purified by recrystallisation? which statement(s) about recrystallisation is/are true? 1. organic compound is more soluble in hot solvent 2. the hot solution is cooled before the purified organic compound is collected 3. the melting point of the purified organic compound is lower than the impure compound - ANSWERSonly 1 & 2 explain why phenol is nitrated more readily than benzene? - ANSWERS(In phenol) a (lone) pair of electrons on O is(partially) delocalised/donated into the pi-system / ring Electron density increases/is higher (than benzene) (phenol) is more susceptible to electrophilic attack OR (phenol) attracts/accepts electrophile/HNO3 more OR (phenol) polarises electrophile/HNO3 more the rate of hydrolysis of a haloalkane depends on the halogen present? - ANSWERSthe weaker the bond the faster the reaction C-F bond is hydrolysed slowest C-I bond is hydrolysed faster than C-Br C-Br has shorter reaction time than C-Cl describe a chemical test to confirm that cinnamaldehyde and methlycinnamaldehyde contain a carbonyl group. how could the products of this test be used to distinguish between the two compound? - ANSWERS(Add) 2,4-dinitrophenylhydrazine AND orange/yellow/red precipitate Take melting point (of crystals) Compare to known values/database E/Z isomerism - ANSWERSthey have different priority groups draw apparatus of distillation - ANSWERSsee image don't forget antibumping granules heat source is water bath draw apparatus of reflux - ANSWERSsee image antibumping granules - no stopper which of these statements about carboxylic acid is true? 1. they react with sodium carbonate to form salts 2. they can be formed by hydrolysing nitriles 3. they react with amines to form amides - ANSWERS1, 2 & 3 why can a molecule form a condensation polymer - ANSWERSit has 2 different functional groups which can release molecules of water Contains a carboxylic acid and an alcohol group; (two) groups react together. to oxidise 2-methylpropan-1-ol to 2-methylpropanal, the student heated the starting material with acidified dichromate & distilled the product as it was formed explain why it was necessary to distil the product as it was formed - ANSWERSprevent further (full) oxidation of the aldehyde to carboxylic acid To remove the product (as it forms) a sample of aspirin is contaminated with salicylic acid recrystallization was used to purify the aspirin describe how recrystallisation is carried out using water as a solvent and explain why recrystallization successfully separates aspirin from the salicylic acid impurities - ANSWERSDESCRIBE - add the mixture to minimum hot water so the SAL & ASP dissolve - Filter when hot - Cool and filter - Wash and dry crystals. EXPLAIN - Aspirin is less soluble in cold water than hot. -When cooled, aspirin comes out of solution and impurities are left behind.