OCR A level Chemistry exam with verified
solutions
The chemist finds the value of Kp is greater when the experiment is repeated at
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a different temperature. Explain whether the temperature is higher or lower in
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the second experiment (2) - correct answer ✔1. Temperature is lower
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2. As the forwards reaction is exothermic
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AND So the position of equilibirum shifted to RHS
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Write an ionic equation for the reaction of aqueous propanoic acid with
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aqueous sodium carbonate - correct answer ✔2H+ + CO3^2- —> H2CO3
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Magnesium chloride has stronger ionic bonds than sodium chloride, explain
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why (3) - correct answer ✔1. Magnesium ion has a greater ionic charge than
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sodium ion AND magnesium has greater charge density
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2. Mg2+ is smaller (due to greater nuclear charge)
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3. Mg2+ has stronger electrostatic forces of attraction to Cl-
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Water is added to the Cu2+/Cu half-cell. Explain , in terms of equilibrium, why
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the cell potential increases - correct answer ✔1. [Cu2+] decrease AND position
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fo equilibrium shifts to the left to restore [Cu2+]
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2. More electrons produced
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3. The cell has a bigger difference in electrode potential
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, How will increasing the concentration of Zn2+ change the cell potential (Zn is
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the positive electrode) - correct answer ✔1. Position of equilibrium shifts to
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the right
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AND more electrons produced, so E° becomes more negative
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2. Smaller difference in electrode potentials created therefore Ecell decreases
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Hey are scientists concerned about the release of methane gas? - correct
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answer ✔1. Methanol contributes to global warming
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Suggest a modification to this experiment, using the same apparatus, which
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would reduce the percentage errors in the measurements. Explain your
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reasoning. - correct answer ✔1. Use a greater mass of Na2O
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2. Larger temperature change to reduce percentage uncertainty
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To produce a more accurate value for percentage by mass of copper? - correct
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answer ✔1. Use a lower concentration of sodium thiosulfate to produce a
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greater titre volume and reduce percentage uncertainty
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2. Repeat titrations and take a mean from concordant results
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3. Use a 3 decimal place balance too reduce percentage uncertainty
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4. Make up a standard solution to 250cm^3
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What can Sulfur acts as? - correct answer ✔A nucleophile
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S has a lone pair of electrons that it can donate
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Are bond enthalpies endothermic or exothermic? - correct answer
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✔endothermic
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solutions
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) - correct answer ✔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 - correct answer ✔2H+ + CO3^2- —> H2CO3
| | | | | | | | | | |
Magnesium chloride has stronger ionic bonds than sodium chloride, explain
| | | | | | | | |
why (3) - correct answer ✔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 - correct answer ✔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) - correct answer ✔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? - correct
| | | | | | | | | | |
answer ✔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. - correct answer ✔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? - correct
| | | | | | | | | | | | |
answer ✔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
| | | | | | | | | |
3. Use a 3 decimal place balance too reduce percentage uncertainty
| | | | | | | | | | |
4. Make up a standard solution to 250cm^3
| | | | | | |
What can Sulfur acts as? - correct answer ✔A nucleophile
| | | | | | | | | |
S has a lone pair of electrons that it can donate
| | | | | | | | | |
Are bond enthalpies endothermic or exothermic? - correct answer
| | | | | | | |
✔endothermic
|
