Misc. Exam Questions

Question 1

Summarise a method of organic purification (7)

Answer 1

• dissolve crude product in HOT solvent
• of MINIMUM volume
• filter to remove insoluble impurities
• cool to recrystallise
• filter under reduced pressure [with buchner/ hirsch apparatus]
• wash with cold solvent
• dry

Question 2

Why may an electric heater be used rather than a bunsen burner?

Answer 2

• many organic compounds are flammable

Question 3

State why reflux may be used in a practical?

Answer 3

• doesn’t allow reactant vapour to escape

Question 4

Give the conditions for hydrogenation.

Answer 4

• H2 present

- Ni [catalyst]

Question 5

Reagents required to synthesise nitriles from aldehydes

Answer 5

• KCN

- acid

Question 6

Describe the apparatus used to remove the drying agent (any insolube solid really) by filtration under reduced pressure

Answer 6

• buchner funnel containing filter paper

- buchner flask connected to vacuum pump

Question 7

Describe a method of determining melting point of a sample

Answer 7

• sample in suitable melting point apparatus (Thiele tube/ melting point apparatus/ capillary in oil bath)
• heat GRADUALLY
• lower melting point/ broad range of melting point indicates an impure sample

Question 8

Explain the bonding in benzene

Answer 8

• each C has 3 covalent bonds
• spare electrons in P orbitals overlap (to form [Pi] cloud)
• delocalisation of electrons occurs

Question 9

Explain the shape of benzene

Answer 9

• planar
• hexagonal ring w 120* bond angles
• C-C bonds are all equal lengths (between those of C-C and C=C)

Question 10

What would be observed when an alcohol reacts with an acyl chloride

Answer 10

• misty/steamy fumes

Question 11

Name the mechanism causing a ketone/aldehyde to be reduced to an alcohol (w NaBH4)

Answer 11

• nucleophillic addition

Question 12

State why it’s better to form primary amines from nitriles rather than halogenoalkanes with ammonia

Answer 12

• (w haloalkanes) further reactions can occur so there’s an impure mixture/ lower atom economy
• (w nitriles) no further reaction so single product formed

Question 13

Which products are formed when magnesium reacts with steam?

Answer 13

• Magnesium oxide

- hydrogen

Question 14

Which amines are strongest in terms of base strength?

Answer 14

• tertiary
• secondary
• primary
• ammonia
• aromatic amines