Q1 V2Fe3+ ions and thiocynanate , SCN- ions react according to the following equilibrium reaction: Fe3+(aq) + SCN-(aq) Fe(SCN)2+(aq) ∆H = - 33.6 kJmol-1 The Fe(SCN)2+ ions formed give the solution a deep red colour. The Fe3+and SCN- ions are colourless in solution. A few drops of SCN- is added to the equilibrium mixture. This will cause the equilibrium to shift to the

Question

Q1 V2Fe3+ ions and thiocynanate , SCN- ions react according to the following equilibrium reaction: Fe3+(aq) +  SCN-(aq) Fe(SCN)2+(aq) ∆H = - 33.6 kJmol-1 The Fe(SCN)2+ ions formed give the solution a deep red colour. The Fe3+and SCN- ions are colourless in solution. A few drops of SCN- is added to the equilibrium mixture. This will cause the equilibrium to shift to the

BlackTom AI · Accepted Answer

To begin, restate the scenario: the equilibrium Fe3+ + SCN- ⇌ FeSCN2+ is exothermic (ΔH = -33.6 kJ/mol), and FeSCN2+ is the pink/red complex while Fe3+ and SCN- are colorless in solution. When a few drops of SCN- are added to the equilibrium mixture, according to Le Châtelier's principle, a perturbation that increases one reactant (SCN-) will drive the equilibrium toward the side that consumes that reactant, i.e., toward the products.

Option a: 'right and the solution to become colourless' would require shifting toward Fe3+ and SCN- (consuming the added SCN-), which is not what adding SCN- does. So this option incorrectly predicts both the direction and the persistence of color.

Option b: 'right and the solution to become darker red' matches the expected outcome: increasing SCN- pushes the equilibrium to the right, forming more FeSCN2+ which imparts a deeper red color to the solution. This aligns with Le Châtelier’s principle and the observed color change described in the scenario.

Option c: 'left and the solution to become colourless' would require shifting away from FeSCN2+, toward Fe3+ and SCN-, the opposite of what adding extra SCN- causes. It also contradicts the color change since the colorless reactants would dominate if the left were favored.

Option d: 'left and the solution to become darker red' again posits a shift to the left, which would not deepen the red color produced by FeSCN2+. The color change would not match a leftward shift, making this option inconsistent with the perturbation.

In summary, adding SCN- increases the concentration of the product FeSCN2+, causing a rightward shift and a darker red solution, while the other options describe incorrect directions of shift or incorrect color outcomes.

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