AS CPACS

Question 1

CPAC 1: Limitations & procedure of measuring molar volume of a gas

Answer 1

Procedure:
- reaction ethanoic acid and CaCO3
- measure CO2 with gas syringe
- repeat for increasing masses of CaCO3
Limitations:
- Gas escapes before bung put on
- some CO2 will dissolve in the water

Question 2

CPAC 2: Tips to make an accurate standard solution

Answer 2

• Wash to make sure all solid is transferred
• Invert to mix solution thoroughly

Question 3

CPAC 3: Uses of pipette and burette in titrations

Answer 3

• Pipette used to accurately measure volume
• ## burette used to add small volumes of liquid

Question 4

CPAC 4: Rate of hydrolysis of haloalkanes
- Why are test tubes left in the water bath
- Why is nitric acid added
- How to measure the rate of hydrolysis

Answer 4

• Test tubes left in water bath to make sure they are all the same temperature
• nitric acid to remove carbonates
• time taken for X to disappear / time for ppte to appear

Question 5

CPAC 5: Oxidation of ethanol
- Why is reflux equipment used
- Why is distillation equipment used

Answer 5

• Fully oxidise the aldehyde
• Stop further aldehyde oxidation
• ABG stop bubbling of liquid & allow smooth boiling

Question 5

CPAC 5: Oxidation of ethanol
- Uses of reflux equipment
- Use of distillation for aldehydes
- Use of anti-bumping granules

Answer 5

• reflux equipment used to fully oxidise the aldehyde
• distil to stop further aldehyde oxidation
• ABG stop bubbling of liquid & allow smooth boiling

Question 6

CPAC 6: Chlorination
- Reactants
- Why is anhydrous CaCl2 used
- Separating aqueous and organic layers
- Removing unreacted acid
- Drying agent for organic layer
- Reason for distillation

Answer 6

• HCl & 2-methylpropan-2-ol
• Ensure any unreacted alcohol is in the aqueous layer
• separating funnel used to separate organic and aq layer by draining
• NaHCO3 solution removes unreacted HCl
• Na2SO4 used to remove water from organic layer
• Distil to purify product

Question 7

CPAC 8: Hess Law enthalpy change
- How to reduce uncertainty
- Why can enthalpy change not be measured directly
- Suggest reasons for differences in experimental and theoretical enthalpy values
- How to get a more accurate experimental value

Answer 7

• larger mass used & greater resolution equipment
• thermal energy needed to start reaction
• Heat loss, incomplete combustion, non standard conditions, water evaporation
• insulate to avoid heat loss and use a digital thermometer