cards I've made from exam paper marking

Question 1

What is average bond enthalpy (2 marks)

Answer 1

Breaking of one mole of bonds

In gaseous molecules

Question 2

How would these two enthalpy changes of hydration differ? (2 marks)

Answer 2

One is smaller

Giving a greater attraction to water

Question 3

How do you calculate percentage dissociation?

Answer 3

[H+]/[HA] x 100

Question 4

What is Kw

Answer 4

1.00x10-14

Question 5

What is the number of hydrogen atoms in 0.125 mol of C2 H5 OH?

Answer 5

0.125 x Avagadro’s Constant x 6

Question 6

Explain why — is an E stereoisomer? (2 marks)

Answer 6

Higher priority groups are on opposite sides

Highest priority groups are (e.g. CHO and C6H5)

Question 7

Explain the difference in boiling point between pentan-1-ol, hexane and heptane? (4 marks)

Answer 7

Heptane has a longer chain so has more points of contact between molecules
Heptane has stronger london forces
Pentan-1-ol has hydrogen bonds that are stronger than
london forces
More energy is required to break hydrogen bonds

Question 8

Describe how a student could obtain a pure sample of crystals (3 marks)

Answer 8

Dissolve in hot solvent
Minimum amount of solvent used
Cool, filter and leave to dry and recrystalise

Question 9

How would you know if a reaction with oxygen has gone to completion?

Answer 9

There is no more mass change

Question 10

What is the purpose of a trial titration?

Answer 10

To find an estimate of the titre

Question 11

How do you find the uncertainty?

Answer 11

Error/Reading x100

x how many readings are taken

Question 12

Why in calorimetry would the experimental value calculated be less exothermic than the actual value?

Answer 12

Incomplete oxidation takes place
Reaction doesn’t go to completion
Not standard conditions used
Heat is lost to surroundings

Question 13

Would heating calorimetry improve accuracy of results?

Answer 13

No as
Larger temperature change decrease in uncertainty
BUT more heat lost to surroundings

Question 14

How would you test for ammonium ions?

Answer 14

Add NaOH and warm
Produces ammonia gas and water
Gas turns red litmus paper blue

Question 15

If the apparatus shown is used why is the product likely to be ethanal? (2 marks)

Answer 15

Volatile components able to distill out

Partial oxidation occurs

Question 16

If the apparatus shown is used why is the product likely to be ethanoic acid? (2 marks)

Answer 16

Volatile components able to distill out

Partial oxidation occurs

Question 17

In terms of orbital overlap explain the similarities and differences between Kekulé’s model and delocalised model of benzene
(3 marks)

Answer 17

Similarities:
Sideways overlap of P orbitals
Pi bonds
Differences: 
Kekulé’s model has alternating pi bonds all of delocalised model electrons overlap

Question 18

Describe how the student can recrystallise the impure crystals to obtain pure benzoic acid (2 marks)

Answer 18

dissolve in minimum amount of hot solvent

cool, filter, leave to dry