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Equilibrium — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryEquilibrium1 Mark
MCQ
Which of the following statements is incorrect?
  • A
    In equilibrium mixture of ice and water kept in perfectly insulated flask mass of ice and water does not change with time.
  • ✓
    The intensity of red colour increases when oxalic acid is added to a solution containing iron $(III)$ nitrate and potassium thiocyanate.
  • C
    On addition of catalyst the equilibrium constant value is not affected.
  • D
    Equilibrium constant for a reaction with negative $\Delta\text{H}$ value decreases as the temperature increases.
✓

Answer

Correct option: B.
The intensity of red colour increases when oxalic acid is added to a solution containing iron $(III)$ nitrate and potassium thiocyanate.
$\text{Fe}^{3+}+\text{SCN}^-\rightleftharpoons\text{FeSCN}^{2+}\text{(Red)}.$
When oxalic acid is added to a solution containing iron nitrate and potassium thiocyanate, oxalic acid reacts with $\text{Fe}{3+}$ ions to form a stable complex ion $[\text{Fe}\text{(C}_2\text{O}_4)3]^{3-},$ thus, decreasing the concentration of free $\text{Fe}^{3+}$ ions which in mm decreases the intensity of red colour.
$\text{Fe}^{3+}+\text{SCN}^-\rightleftharpoons\text{[Fe(SCN)}]^{2+}\text{(Red)}.$

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