Chemistry_2013_STPM term 3_Objectives

How many C − C sigma bonds are in the molecule?

• 5

• 6

• 10

• 11

Based on the data given, which statement is true?

• Anilinium ion is the most acidic species.

• 4 − Nitroanilinium ion is the most stable species.

• 4 − Nitroanilinium is more stable than 4 − nitrobenzoate ion.

• Nitrobenzoate ion is a weaker conjugate base than 4 − nitrobenzoate ion.

Which statement about the reaction between methybenzene and chlorine in the presence of light is true?

• The reaction is a free − radical addition reaction.

• Hydrogen chloride is formed in the termination step.

• ( Chloromethyl) benzene is formed in the first propagation step.

• 1 − Chloro − 4 − methylbenzene is one of the products of the reaction.

Answer explanation

A is incorrect. The reason is a free radical substitution (sunlight is required). Arenes seldom undergo addition because of the stability of benzene ring.

B is incorrect. Chlorine is formed in the termination step.

C is incorrect. (Chloromethyl) Bezene is formed in the second step in propagation.

D is incorrect. Refers to electrophilic substitution which requires AlCl₃ as catalyst.

Ethene undergoes addition reaction due to the presence of C = C bond. Which is not true of the bromination of ethene?

• The C = C bond readily accepts as electrophile.

• Bromonium ion is formed as an intermediate.

• A π bond is converted to a σ bond.

• The product formed is 1, 1 − dibromoethane.

Ethylbenzene reacts with concentrated nitric acid and concentrated sulphuric acid followed by acidified potassium manganate (VII). What is the structure formula of the product formed?

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Compound X is produced from catalytic oxidation of an alkene. It has the percentage composition by mass : carbon 38.7%, hydrogen 9.70%, oxygen 51.6%. When 0.890 g of X is heated at 400K, the vapour produced occupies a volume of 477cm³ at 100kPa. Which statement about X is not true? [ The gas constant, R, is 8.31 J K^-1 mol^-1 ]

• The empirical formula of X is CH₃O

• Compound X is 1 , 2 − ethanediol

• One mole of X reacts with Na releasing two moles of H₂ gas.

• Compound X is used as an antifreeze in the radiator.

Which organic compound produces a white precipitate in the shortest possible time when its solution is shaken vigorously with an ethanolic silver nitrate solution at room temperature?

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Chloroethane hydrolyses easily in an aqueous of sodium hydroxide whereas hydrolysis of chlorobenzene requires high temperature and pressure. Which statement best explains the low reactivity of chlorobenzene toward hydrolysis?

• The non − bonding electrons of Cl are delocalised into the benzene ring.

• The Cl atom withdraws the electron clouds from the benzene ring.

• The Cl atom is strongly bonded to the benzene ring.

• The C − Cl bond in chlorobenzene is shorter.

Which compound forms a white precipitate when heated with an aqueous solution of sodium hydroxide followed by acidification?

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Phenylethene is produced when compound X reacts with concentrated sulphuric at 180°C. What could compound X be?

• Phenylmethanol

• 2 − Phenylmethanol

• 1 − Phenyl − 1 − propanol

• 2 − Phenyl − 1 − propanol