Chemistry Paper 1B Latest Examination Questions with Verified A+ Answers
2026 Latest Updated Version.
What is the purpose of recrystallisation? To purify an impure solid by using differences in solubility
between the desired product and impurities.
Describe how recrystallisation is carried out - Dissolve the impure solid in the minimum volume of hot
(4 marks) solvent.
- Filter the hot solution to remove insoluble impurities.
- Allow the solution to cool slowly so crystals form.
- Filter off the crystals and rinse them with a small quantity of
cold solvent.
What is the most important factor when The desired solid (slid being purified) should be very soluble
choosing a solvent for recrystallisation? in hot solvent but not very soluble in cold solvent - The
solubility should vary significantly with temperature.
Why should the solid be dissolved in the To maximise the yield and purity of solid formed
minimum volume of hot solvent for Too much solvent: low/decreased yield (but pure) , because
recrystallisation? some product remains dissolved in the solution after
cooling.
Too little solvent: low/decreased purity (but high yield),
because the solid or impurities may not fully dissolve.
How to remove more and less soluble Less soluble impurity removed by filtering hot solution from
impurities in recrystallisation? solids.
More soluble impurity removed by removing/filtering crystals
from cold solution.
Why are crystals washed with a small To remove soluble impurities from the surface of the crystals
quantity of cold solvent in while minimising loss of product.
recrystallisation?
What is the purpose of calorimetry? To measure heat energy changes in reactions by measuring a
temperature change. Used to calculate enthalpy changes.
, What equation is used in calorimetry? q = mcΔT
q = heat energy
transferred m = mass
of solution/water c
= specific heat
capacity ΔT =
temperature
change
For enthalpy change per mole:
ΔH=-q/n(moles)
Describe a calorimetry experiment to - Measure a known mass/volume of water in a copper can
measure the enthalpy of combustion of a and record its initial temperature.
fuel. [4 marks] - Measure the mass of the spirit burner before burning.
- Burn the fuel to heat the water and record the final temperature.
- Measure the mass of the spirit burner after burning
and use q = mcΔT to calculate the energy released.
How to make calorimetry results more - Use and insulated cup (calorimeter) to reduce heat loss to the
accurate? surroundings
- Use a lid to reduce heat loss and evaporation
- Stir mixture to ensure the temperature is uniform throughout
the solution
What are the key assumption in simple - The solution has the same specific heat capacity as water (4.18
calorimetry? J/K/mol)
- The density of the solution is 1.00 g cm⁻r (same as water), so
mass(g)=volume(cmr)
- No heat is lost to the surroundings (all heat is transferred to
the water/solution)
- The calorimeter does not absorb significant heat
What are the main sources of error in - Heat loss to surroundings (temperature rise and calculated
calorimetry? enthalpy is smaller)
- Incomplete combustion (Less energy is released, so the
temperature rise and calculated enthalpy is smaller)
- Evaporation of fuel.
- Heat absorbed by the copper can.
- Soot formation on the can.
2026 Latest Updated Version.
What is the purpose of recrystallisation? To purify an impure solid by using differences in solubility
between the desired product and impurities.
Describe how recrystallisation is carried out - Dissolve the impure solid in the minimum volume of hot
(4 marks) solvent.
- Filter the hot solution to remove insoluble impurities.
- Allow the solution to cool slowly so crystals form.
- Filter off the crystals and rinse them with a small quantity of
cold solvent.
What is the most important factor when The desired solid (slid being purified) should be very soluble
choosing a solvent for recrystallisation? in hot solvent but not very soluble in cold solvent - The
solubility should vary significantly with temperature.
Why should the solid be dissolved in the To maximise the yield and purity of solid formed
minimum volume of hot solvent for Too much solvent: low/decreased yield (but pure) , because
recrystallisation? some product remains dissolved in the solution after
cooling.
Too little solvent: low/decreased purity (but high yield),
because the solid or impurities may not fully dissolve.
How to remove more and less soluble Less soluble impurity removed by filtering hot solution from
impurities in recrystallisation? solids.
More soluble impurity removed by removing/filtering crystals
from cold solution.
Why are crystals washed with a small To remove soluble impurities from the surface of the crystals
quantity of cold solvent in while minimising loss of product.
recrystallisation?
What is the purpose of calorimetry? To measure heat energy changes in reactions by measuring a
temperature change. Used to calculate enthalpy changes.
, What equation is used in calorimetry? q = mcΔT
q = heat energy
transferred m = mass
of solution/water c
= specific heat
capacity ΔT =
temperature
change
For enthalpy change per mole:
ΔH=-q/n(moles)
Describe a calorimetry experiment to - Measure a known mass/volume of water in a copper can
measure the enthalpy of combustion of a and record its initial temperature.
fuel. [4 marks] - Measure the mass of the spirit burner before burning.
- Burn the fuel to heat the water and record the final temperature.
- Measure the mass of the spirit burner after burning
and use q = mcΔT to calculate the energy released.
How to make calorimetry results more - Use and insulated cup (calorimeter) to reduce heat loss to the
accurate? surroundings
- Use a lid to reduce heat loss and evaporation
- Stir mixture to ensure the temperature is uniform throughout
the solution
What are the key assumption in simple - The solution has the same specific heat capacity as water (4.18
calorimetry? J/K/mol)
- The density of the solution is 1.00 g cm⁻r (same as water), so
mass(g)=volume(cmr)
- No heat is lost to the surroundings (all heat is transferred to
the water/solution)
- The calorimeter does not absorb significant heat
What are the main sources of error in - Heat loss to surroundings (temperature rise and calculated
calorimetry? enthalpy is smaller)
- Incomplete combustion (Less energy is released, so the
temperature rise and calculated enthalpy is smaller)
- Evaporation of fuel.
- Heat absorbed by the copper can.
- Soot formation on the can.
