cards I've made from exam paper marking Flashcards
What is average bond enthalpy (2 marks)
Breaking of one mole of bonds
In gaseous molecules
How would these two enthalpy changes of hydration differ? (2 marks)
One is smaller
Giving a greater attraction to water
How do you calculate percentage dissociation?
[H+]/[HA] x 100
What is Kw
1.00x10-14
What is the number of hydrogen atoms in 0.125 mol of C2 H5 OH?
0.125 x Avagadro’s Constant x 6
Explain why — is an E stereoisomer? (2 marks)
Higher priority groups are on opposite sides
Highest priority groups are (e.g. CHO and C6H5)
Explain the difference in boiling point between pentan-1-ol, hexane and heptane? (4 marks)
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
Describe how a student could obtain a pure sample of crystals (3 marks)
Dissolve in hot solvent
Minimum amount of solvent used
Cool, filter and leave to dry and recrystalise
How would you know if a reaction with oxygen has gone to completion?
There is no more mass change
What is the purpose of a trial titration?
To find an estimate of the titre
How do you find the uncertainty?
Error/Reading x100
x how many readings are taken
Why in calorimetry would the experimental value calculated be less exothermic than the actual value?
Incomplete oxidation takes place
Reaction doesn’t go to completion
Not standard conditions used
Heat is lost to surroundings
Would heating calorimetry improve accuracy of results?
No as
Larger temperature change decrease in uncertainty
BUT more heat lost to surroundings
How would you test for ammonium ions?
Add NaOH and warm
Produces ammonia gas and water
Gas turns red litmus paper blue
If the apparatus shown is used why is the product likely to be ethanal? (2 marks)
Volatile components able to distill out
Partial oxidation occurs
If the apparatus shown is used why is the product likely to be ethanoic acid? (2 marks)
Volatile components able to distill out
Partial oxidation occurs
In terms of orbital overlap explain the similarities and differences between Kekulé’s model and delocalised model of benzene
(3 marks)
Similarities: Sideways overlap of P orbitals Pi bonds Differences: Kekulé’s model has alternating pi bonds all of delocalised model electrons overlap
Describe how the student can recrystallise the impure crystals to obtain pure benzoic acid (2 marks)
dissolve in minimum amount of hot solvent
cool, filter, leave to dry
