Chemistry_2016_STPM term 3_Objectives

Which compound is made up of 87.8% carbon and 12.2% hydrogen by mass?

• CH₃CH=CHCH₂CH₂CH₃

• H₂C=CHCH₂CH₂CH=CH₂

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Answer explanation

An organic compound which shows cis-trans isomerism is

• 1-bromo-2-methylpropene

• 1, 1-dibromo-2-methylpropene

• 2, 3-dibromo-2-butene

• 1-bromo-1-chloro-2-methyl 1-butene

Answer explanation

Which compound has one tertiary carbon atom?

• Butane

• Ethylbenzene

• Methylpropane

• Dimethylpropane

Answer explanation

An organic compound undergoes oxidation and addition reactions with acidified potassium permanganate solution under different conditions. The compound is

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Answer explanation

Oxidation and addition with KMnO₄ indicates the presence of non-aromatic C = C bonds.

Two possible answer is A and C

1 , 1-Dichloroethane and 1 , 2-Dichloroethane are structural isomers. What are the products formed when both isomers are hydrolysed separately in dilute hydrochloric acid?

• HOCH₂CH₂OH and CH₃CHO

• HOCH₂CH₂OH and CH₃CH(OH)₂

• HOCH₂CH₂Cl and CH₃CHO

• HOCH₂CH₂OH and CH₃CH(OH)Cl

Answer explanation

Which reaction represents a substitution reaction which occurs through nucleophilic mechanism?

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Answer explanation

Nucleophilic substitution is exhibited by haloakanes :

R — X + Nu^- → R — Nu + X^-

Option A is electrophilic substitution.

Option B is electrophilic substitution.

Option D is electrophilic addition.

A compound , X, is a crystal with an antiseptic smell. X can be used to synthesise compound with a structural formula CH₃COOC₆H₅ by firstly forming Y as in the reaction scheme shown.

What suitable reagents are used in Step Ⅰ and Step Ⅱ?

• Step Ⅰ : Na

  Step Ⅱ : CH₃COCI

• Step Ⅰ : NaOH

  Step Ⅱ : CH₃CONH₂

• Step Ⅰ : PCl₅

  Step Ⅱ : CH₃COO^- Ag⁺

• Step Ⅰ : PCl₅

  Step Ⅱ : C₆H₅COCI

Answer explanation

Compound X dissolves in an aqueous sodium hydroxide solution but does not dissolves in an aqueous sodium carbonate solution. Compound X maybe

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Answer explanation

Phenol and benzoic acid are soluble in NaOH. However, phenol (a weak acid) is insoluble in sodium carbonate, but benzoic acid do. So, the answer is B.

Carbonyl compounds can be prepared from alcohols using acidified potassium dichromate. Which alcohol can be used to produced a ketone?

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Answer explanation

A secondary alcohol on oxidation produces a ketone. Primary alcohol on oxidation produces a carboxylic acid.

Tertiary alcohol is not oxidisable.

Glucose is an example of a naturally occurring aldehyde. Which is not true about glucose?

• Glucose can be reduced.

• Glucose reacts with alkaline iodine.

• Glucose can undergo polymerisation.

• Glucose reacts with 2 , 4-dinitrophenylhydrazine.

Answer explanation

This is the structure of glucose.

Being an aldehyde, it can be reduced.

There is no methyl-ketone group, CH₃ — C = O.

Thus it does not give a positive iodoform test. Polymerisation of glucose gives starch or cellulose. The aldehyde group in glucose gives a positive test with 2 , 4-dinitrophenylhydrazine.