A-LEVEL JUNE 2024 OCR CHEMISTRY A PAPER 1 MARK SCHEME
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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) - 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 - ANSWER 2H+ + CO3^2- —> H2CO3 Magnesium chloride has stronger ionic bonds than sodium chloride, explain why (3) - 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 - 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) - 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? - 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. - 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? - 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? - ANSWER A nucleophile S has a lone pair of electrons that it can donate Are bond enthalpies endothermic or exothermic? - ANSWER endothermic Is second electron affinity endothermic [Show More]
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