Organic and Physical Chemistry

Question 1

How does a Maxwell–Boltzmann distribution curve change if the temperature is lowered?

Answer 1

Peak shifts to the left more particle have fewer energy.

Question 2

Explain the effect that lowering the temperature would have on the rate of reaction.

Answer 2

Fewer particles will have energy greater than or equal to the activation energy
Fewer successful collisions in a given time

Question 3

State the type of isomerism shown by branched isomers.

Answer 3

Chain isomerism

Question 4

Suggest how partial blockage might affect the performance of a helicopter engine.

Answer 4

The engine is less efficient therefore there will be increased costs as it will be using more fuel.

Question 5

1,1,2-Trichloro-1,2,2-trifluoroethane was banned for use as a refrigerant because it damaged the ozone layer.
Write three equations to show how this compound is involved in damaging the ozone layer.

Answer 5

CCl2FCF2Cl –> Cl• + CCl2FCF2.
Cl• + O3 –> ClO• + O2
ClO• + O3 –> 2O2 + Cl•

Question 6

State the role of chlorine atoms in free radical substitution.

Answer 6

acts as a catalyst

Question 7

Deduce which of the following coolants, A, B or C, would cause least environmental damage to the atmosphere.

CHCl2CHClF CF3CH2F CF3CCl2F
A B C

Answer 7

B CF3CH2F

Question 8

IUPAC name for CF3CH2F.

Answer 8

1,1,1,2-tetrafluoroethane

Question 9

Explain why iodomethane has the higher boiling point by considering the forces that act between CH3I molecules and comparing these forces with the forces between the CH3F molecules.

Answer 9

Iodine is bigger than fluorine so the van der Waals forces between CH3I molecules are stronger than those between CH3F molecules.

The dipole-dipole forces between CH3F molecules are stronger than those between CH3I molecules.

The van der Waals forces are stronger than the dipole-dipole forces so these dominate.

Question 10

Name the reagent(s) that can be used to determine pent-1-ene and what observation will be made.

Answer 10

Bromine (water)

Colour change from orange to colourless

Question 11

Name the reagent(s) that can be used to identify pentanoic acid and what observation will be made.

Answer 11

Test the pH with named indicator (eg Universal Indicator)

Propanoic acid would turn Universal Indicator red

Question 12

Name the reagent(s) that can be used to identify pentanal and what observation will be made.

Answer 12

Tollen’s reagent

(Colourless solution to) silver mirror

Question 13

Explain why the two products are formed in different in mechanisms amounts.

Answer 13

The major product is formed via a tertiary carbocation intermediate and the minor product is formed via a secondary carbocation intermediate
The tertiary carbocation is more stable than the secondary carbocation

Question 14

Describe how the students would use this apparatus to collect a sample of ethanol.
Include in your answer the functions of the parts of the apparatus labelled A, B and C.

Answer 14

Stage 1
• Turn on the water.
• Heat the flask, with a Bunsen burner.
• This causes water and ethanol vapours to be produced.
Stage 2
• Vapours pass up the fractionating column A.
• Water and ethanol are separated in column A.
• Water condenses back into the flask in column A.
Stage 3
• Observe the thermometer at B to keep the temperature at or below the boiling point of ethanol.
• Only ethanol vapour (with a little water) passes into the condenser.
• Use the condenser at part C to cool the vapours and condense the ethanol back into a liquid.

Question 15

• Which of the following mechanisms does not occur in reactions of bromoethane?

Answer 15

Electrophilic addition

Question 16

• What is the empirical formula of 4-hydroxypent-2-ene?

Answer 16

C^5H^10O

Question 17

• What is the total number of structural isomers with the molecular formula C2HBrClF3?

Answer 17

4

Question 18

• Which of the following contains the most chloride ions?

Answer 18

30 cm3 of 5.50 × 10−2 mol dm−3 calcium chloride solution

Question 19

• Which is a pair of functional group isomers?

Answer 19

hexagon shape

Question 20

• The equation for the hydrogenation of ethyne is
  C2H2 + 2H2 C2H6
  The experimental yield is 65.0%.
  What is the mass in grams of ethane that can be produced from 16.20 g of hydrogen?

Answer 20

78.98 g

Question 21

• Which molecule does not have a permanent dipole?

Answer 21

CF4

Question 22

• Bromine exists as two isotopes 79Br and 81Br, which are found in almost equal abundance.
  Which of the statements is correct?

Answer 22

The mass spectrum of C3H7

Question 23

• Which of these species is not planar?

Answer 23

CH3OH

Question 24

• Which of the arrows, labelled A, B, C or D in the mechanism in Figure 6,
  is not correct?

Answer 24

C

Question 25

• Z-Retinal, shown in Figure 7, is a component in vitamin A.

Which of the double bonds, labelled A, B, C or D, is responsible for the letter Z in the name?

Answer 25

C

Question 26

• Which line represents the volume of hydrogen formed, at the same temperature and pressure, when the concentration of sulfuric acid has been halved?

Answer 26

Exact half A

Question 27

• The maximum uncertainty when weighing 0.250 g on a balance was 0.001 g.
  What is the percentage uncertainty?

Answer 27

0.4%

Question 28

• Which species has the same number of electrons as the radical •CH3?

Answer 28

CH4+

Question 29

• Which of these infrared spectra could represent a carboxylic acid?

Answer 29

A