Photo AI
This question is about a reversible reaction - AQA - GCSE Chemistry - Question 10 - 2020 - Paper 2
Question 10
This question is about a reversible reaction. The reaction between solutions of iron(III) ions (Fe³⁺) and thiocyanate ions (SCN⁻) is reversible. The ionic equation... show full transcript
Worked Solution & Example Answer:This question is about a reversible reaction - AQA - GCSE Chemistry - Question 10 - 2020 - Paper 2
Step 1
Step 2
A few drops of a colourless solution containing a high concentration of thiocyanate ions (SCN⁻) are added to the orange equilibrium mixture. Explain the colour change observed.
Answer
When a few drops of a colourless solution containing a high concentration of thiocyanate ions (SCN⁻) are added, the colour of the equilibrium mixture becomes more red. This occurs because the position of equilibrium shifts to the right, favoring the formation of the red FeSCN²⁺ complex. Consequently, the concentration of FeSCN²⁺ ions increases, resulting in a deeper red coloration.
Step 3
A water bath is set up at a temperature above room temperature. When a test tube containing the orange equilibrium mixture is placed in the water bath, the mixture becomes more yellow. Explain what this shows about the energy change for the forward reaction.
Answer
Placing the orange equilibrium mixture in a water bath at a higher temperature causes the mixture to become more yellow, indicating that the forward reaction is exothermic. According to Le Chatelier's principle, increasing the temperature shifts the equilibrium position to the left, towards the reactants (Fe³⁺ and SCN⁻), which reduces the concentration of the products (FeSCN²⁺) and results in a more yellow solution.
Step 4
Explain why a change in pressure does not affect the colour of the equilibrium mixture.
Answer
A change in pressure does not affect the colour of the equilibrium mixture because the reaction involves only aqueous solutions, with no gaseous reactants or products present. According to Le Chatelier's principle, changes in pressure influence reactions involving gases, while solutions remain unaffected.
Step 5