DF aprst: Polymers; ideal gas equation; isomerism

Question 1

What is a co-polymer?

Answer 1

A polymer derived from 2+ species of monomer.

Question 2

Describe the structure of an A-B polymer.

Answer 2

Arrangement regular + alternating.

Question 3

What is a benzene group otherwise known as?

Answer 3

A phenyl group.

Question 4

Suggest the mechanism by which addition polymerisation occurs.

Answer 4

Electrophilic addition

Double bond attacks an electrophile, forming a carbocation which further double bonds attack in a domino-like manner

Question 5

Answer 5

But-1-ene + propene

Question 6

Draw the repeating unit of the A-B copolymer formed when chloroethene and ethenyl ethanoate undergo addition polymerisation.

Answer 6

Ethenyl ethanoate = CH₃COOCH=CH₂

Question 7

Why does one mole of a gas always occupy 24 dm³ at RTP, regardless of the size of gas molecules?

Answer 7

Variations in molecular size are negligable compared to the distance between molecules.

Question 8

What is standard temperature?

Answer 8

273 K

0^oC

Question 9

What volume of air is needed to completely burn 15 cm³ of hexane vapour? Assume that all volumes are measured at RTP and that air contains 21% oxygen.

Answer 9

C₆H₁₄ + 9.5O₂ → 6CO₂ + 7H₂O

Equal moles of any two gases occupy the same volume at RTP

Vol O₂ = 15 x 9.5 = 142.5 cm³

Vol air = 142.5 x 100/21 = 680 cm³

Question 10

• State the ideal gas equation.
• State the units used for each quantity, excluding the constant.

Answer 10

PV = nRT

• P in Pa (Nm^-1)
• V in m³
• n in mol
• T in K

Question 11

What is the volume of 1 mole of a gas, in dm³, at 100 kPa and 16^oC?

Answer 11

PV = nRT so V = nRT/P

P = 100 kPa = 100 x 10³ Pa

T = 16^oC = 289 K

V = 1 x 8.314 x 289 / (100 x 10³) = 0.024 m³ = 24 dm³

Question 12

The following shows the complete combustion of octane:

C₈H₁₈(g) + 12.5O₂(g) → 8CO₂(g) + 9H₂O(g)

3.42 g of octane is burned per second in an engine. The exhaust gases are produced at 550^oC and 1.50 x 10⁵ Pa.

Calculate the volume of exhaust gases, in dm³, produced per second. Assume that carbon dioxide and water vapour are the only gases present in the exhaust.

Answer 12

Rearrange equation

pV = nRT → V = nRT/P

Find n, combined mol of CO₂ + H₂O

n octane = 3.42/114 = 0.03

Therefore n (CO₂ + H₂O) = 0.03 x (8 + 9) = 0.51 mol

Convert temperature

550^oC + 273 = 823 K

Find volume in m³ and convert to dm³

V = (0.51 x 8.314 x 823) / (1.5 x 10⁵) = 0.0233 m³

x 10³ = 23.3 dm³

Question 13

Hydrogen can be stored in car tanks at a pressure of 7.0 × 10⁴ kPa.

The volume of a tank is 70 dm³ and the temperature 20°C. Calculate the maximum energy that could be produced by burning all the hydrogen in the tank.

∆_cH for H₂ = –242 kJ mol^-1

Give your answer in standard form, to two significant figures.

Answer 13

pV = nRT → n = PV/RT

P = 7 x 10⁴ kPa = 7 x 10⁷ Pa

V = 70 dm³ = 70 x 10^-3 m³

T = 20^oC = 293 K

Mol H₂ = n = (7 x 10⁷ x 70 x 10^-3) / (8.314 x 293) = 2011 mol

E = 2011 x 242 = 490,000 kJ = 4.9 x 10⁵ kJ

Question 14

What are structual isomers?

Answer 14

• Same molecular formulae
• Different structural formulae (ordering of atoms)

Question 15

Name and describe the 3 types of structural isomerism.

Answer 15

Chain: different branching of chains; 4+ carbons needed

Position: different locations of a functional group

Functional group: different functional groups / homologous series

Question 16

What are stereo isomers?

Answer 16

• Same molecular formulae
• Same structural formulae (ordering of atoms)
• Different spatial arrangement of atoms

Question 17

Name and define the 2 types of stereoisomerism. State any requirements for each type to arise.

Answer 17

E/Z or cis/trans or geometric: Lack of free rotation about C=C bonds with different groups on each carbon:

• Z/cis: same groups on upper or lower side of double bond (“zame side”)
• E/trans: same groups on opposite upper/lower sides of double bond

Optical: Isomers are mirror images of each other; must be non-symmetrical

Question 18

• Name these molecules
• Which type of isomerism is shown here?

Answer 18

• Butane + methylpropane
• Chain structural isomerism

Question 19

• Name these molecules
• Which type of isomerism is shown here?

Answer 19

• Propan-1-ol + propan-2-ol
• Position structural isomerism

Question 20

• Name these molecules and state the homologous series to which they belong
• Which type of isomerism is shown here?

Answer 20

• Propan-1-ol (alcohol, -OH) + methoxyethane (ether, -O-)
• Functional group structural isomerism

Question 21

• Name these molecules
• Which type of isomerism is shown here?

Answer 21

• E(trans)-but-2-ene, Z(cis)-but-2-ene
• E/Z or cis/trans or geometrical stereo isomerism

Question 22

Answer 22

a) E/Z isomers
b) 2 mol
c) Citranellol has 1 fewer double bonds / is partially hydrogenated
d) Position structural isomers