In solution, pale yellow-coloured Fe³⁺(aq) and colourless SCN⁻(aq) form an equilibrium with FeSCN²⁺(aq) - VCE - SSCE Chemistry - Question 6 - 2006 - Paper 1
Question 6
In solution, pale yellow-coloured Fe³⁺(aq) and colourless SCN⁻(aq) form an equilibrium with FeSCN²⁺(aq). FeSCN²⁺(aq) is red in colour.
Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺... show full transcript
Worked Solution & Example Answer:In solution, pale yellow-coloured Fe³⁺(aq) and colourless SCN⁻(aq) form an equilibrium with FeSCN²⁺(aq) - VCE - SSCE Chemistry - Question 6 - 2006 - Paper 1
Step 1
Sample 1: 1 drop of a concentrated solution of Ag⁺(aq) is added, which forms a AgSCN precipitate.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
I. Colour will be less red since the equilibrium shifts left to compensate for the removal of SCN⁻.
II. The concentration of [Fe³⁺] will decrease as the reaction shifts left.
Step 2
Sample 2: 1 drop of a concentrated solution of Fe³⁺(aq) is added.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
I. Colour will be more red as the increase in Fe³⁺ pushes the equilibrium to the right.
II. The concentration of [Fe³⁺] will increase due to the additional Fe³⁺ added.
Step 3
Sample 3: 1 drop of a concentrated solution of HPO₄²⁻(aq) is added, which forms colourless FeHPO₄(aq).
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
I. Colour will be less red since the equilibrium shifts left due to decreased Fe³⁺ availability.
II. The concentration of [Fe³⁺] will decrease as some Fe³⁺ reacts to form FeHPO₄.
Step 4
Sample 4: Addition of a large volume of water.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
I. Colour will be less red as dilution reduces the concentration of all species.
II. The concentration of [Fe³⁺] will decrease due to dilution.
Step 5
b. Sketch the changes that would be expected to occur to these concentrations if the temperature of the equilibrium mixture was increased.
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
As the reaction is exothermic, increasing the temperature will shift the equilibrium to the left, favoring the reactants. Therefore, the concentrations would show a decrease in [FeSCN²⁺] and an increase in both [Fe³⁺] and [SCN⁻], illustrated as:
