Paper 3 chemistry - experiments and synthetic routes !

Question 1

how would i test halogen reactivity when give KI,KBr,KCl and the pure forms of the halogens i.e.: cl2 br2 and i2 ?
1 mark

Answer 1

• react them with each other and the more reactive ones should displace the others
  =DISPLACEMENT REACTION

Question 2

how would you produce lactic acid from an aldehyde ?
2 steps
7 marks

Answer 2

lactic acid :
1-aldehyde + HCN => nucleophilic addition , heat and reflux
2-Hydrolysis of a nitrile =REFLUX with H2SO4 to produce a carboxylic acid and NH4+

Question 3

why would a substance leave a stationary phase slowly ?

Answer 3

• better adsorption to the stationary phase i.e. : more positive charge

Question 4

reasons for different values for combustion ?

Answer 4

1- incomplete combustion
2-specific heat capacity of calorimeter not taken into account
3-heat loss to surroundings
4-evaporation of solvent

Question 5

why would enthalpy change of combustion change when you use a different calorimeter at a lower temperature of 60 ?

Answer 5

1-less exothermic as energy is used to boil the water

Question 6

what does grignard reagent do ? 1

Answer 6

produce an alcohol- increases carbon chain length

- nucleophile thats a reducing agent

Question 7

colour of KMNO4 ?

Answer 7

pale pink /purple to colourless

Question 8

how do you ensure something is fully decomposed ?

Answer 8

• heat until it has a constant mass

Question 9

how do you reduce percentage uncertainty ?

Answer 9

1- use a larger mass

2-mass balance which goes to 3dp rather than 2dp