Page 35 - Chemistry - XI

8. In test tube b, add 1 mL of HCl solution. Shake the solution well and compare the intensity of the
colour with the solution of test tube a.

9. In test tube c add 1 mL of CoCl solution and compare the intensity of colour with the solution of test
2
tube a.
10. Similarly repeat the observations with the solutions of test tubes d, e, f, g by adding various amounts
of HCl and CoCl solutions separately. Record your observations in a tabular form.
2
Test Amount of Amount of CoCl Eff ect on Eff ect on the Direction of
Tube HCl solution solution added 2 the colour [Co(H O) )] ions the shift of
2+
6
2
added intensity concentration equilibrium
(a)
(b)

(c)
(d)
(e)

(f)
(g)

Result

1. The equilibrium shifts towards forward direction by adding chloride ions, therefore the intensity of
blue colour increases because of the increase in [CoCl ] ions concentration.
2–
4
2. The increase in water concentration shifts the equilibrium to the left, therefore the intensity of blue
colour decreases and pink colour increases because of increase in [Co(H O) ] ions.
2+
2 6
Precautions

1. Concentration of HCl and CoCl solutions should be accurate.
2
2. The concentration of Cl should not be greater than six times to that of H O.
–
2
3. Comparison of colour of the solutions must be done by keeping the reference solutions side by side.

VIVA VOCE

Q1. What is equilibrium constant (K) and how does it diff er from the rate constant?
Ans. K is applicable to reversible reaction, K = k /k . Rate constant k belongs to forward reaction, k is
b
a
b
a
rate constant for backward reaction. Rate constant is applicable to single reaction (irreversible).
Q2. What will be the eff ect of adding solid KCl to Fe +CN [Fe(SCN)]?
3+
2+
−
S

Ans. The equilibrium will shift in backward direction, i.e. intensity of red colour will decrease.
3+
2+
Q3. Explain why representing the ionic reaction Fe (aq) +SCN (aq) [Fe(SCN)](aq) is
−

more appropriate in the following form.
3+
[Fe(HO)] +SCN [Fe(HO)SCN] +H O
2+
−

2
6
2
5
2
Ans. It is because coordination number of Fe is 6 in presence of water (H O) molecule.
3+
2
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