OCR A level Chemistry Mark Scheme
The chemist finds the value of Kp is greater when the experiment is repeated at a
different temperature. Explain whether the temperature is higher or lower in the
second experiment (2) - Ans>>1. Temperature is lower
2. As the forwards reaction is exothermic
AND So the position of equilibirum shifted to RHS
Write an ionic equation for the reaction of aqueous propanoic acid with aqueous
sodium carbonate - Ans>>2H+ + CO3^2- —> H2CO3
Magnesium chloride has stronger ionic bonds than sodium chloride, explain why (3)
- Ans>>1. Magnesium ion has a greater ionic charge than sodium ion AND
magnesium has greater charge density
2. Mg2+ is smaller (due to greater nuclear charge)
3. Mg2+ has stronger electrostatic forces of attraction to Cl-
Water is added to the Cu2+/Cu half-cell. Explain , in terms of equilibrium, why the
cell potential increases - Ans>>1. [Cu2+] decrease AND position fo equilibrium
shifts to the left to restore [Cu2+]
2. More electrons produced
3. The cell has a bigger difference in electrode potential
How will increasing the concentration of Zn2+ change the cell potential (Zn is the
positive electrode) - Ans>>1. Position of equilibrium shifts to the right
AND more electrons produced, so E° becomes more negative
2. Smaller difference in electrode potentials created therefore Ecell decreases
Hey are scientists concerned about the release of methane gas? - Ans>>1.
Methanol contributes to global warming
Suggest a modification to this experiment, using the same apparatus, which would
reduce the percentage errors in the measurements. Explain your reasoning. -
Ans>>1. Use a greater mass of Na2O
2. Larger temperature change to reduce percentage uncertainty
To produce a more accurate value for percentage by mass of copper? - Ans>>1.
Use a lower concentration of sodium thiosulfate to produce a greater titre volume
and reduce percentage uncertainty
2. Repeat titrations and take a mean from concordant results
The chemist finds the value of Kp is greater when the experiment is repeated at a
different temperature. Explain whether the temperature is higher or lower in the
second experiment (2) - Ans>>1. Temperature is lower
2. As the forwards reaction is exothermic
AND So the position of equilibirum shifted to RHS
Write an ionic equation for the reaction of aqueous propanoic acid with aqueous
sodium carbonate - Ans>>2H+ + CO3^2- —> H2CO3
Magnesium chloride has stronger ionic bonds than sodium chloride, explain why (3)
- Ans>>1. Magnesium ion has a greater ionic charge than sodium ion AND
magnesium has greater charge density
2. Mg2+ is smaller (due to greater nuclear charge)
3. Mg2+ has stronger electrostatic forces of attraction to Cl-
Water is added to the Cu2+/Cu half-cell. Explain , in terms of equilibrium, why the
cell potential increases - Ans>>1. [Cu2+] decrease AND position fo equilibrium
shifts to the left to restore [Cu2+]
2. More electrons produced
3. The cell has a bigger difference in electrode potential
How will increasing the concentration of Zn2+ change the cell potential (Zn is the
positive electrode) - Ans>>1. Position of equilibrium shifts to the right
AND more electrons produced, so E° becomes more negative
2. Smaller difference in electrode potentials created therefore Ecell decreases
Hey are scientists concerned about the release of methane gas? - Ans>>1.
Methanol contributes to global warming
Suggest a modification to this experiment, using the same apparatus, which would
reduce the percentage errors in the measurements. Explain your reasoning. -
Ans>>1. Use a greater mass of Na2O
2. Larger temperature change to reduce percentage uncertainty
To produce a more accurate value for percentage by mass of copper? - Ans>>1.
Use a lower concentration of sodium thiosulfate to produce a greater titre volume
and reduce percentage uncertainty
2. Repeat titrations and take a mean from concordant results
