Page 33 - Chemistry - XI

Procedure
1. Prepare 50 mL solutions each of FeCl and NH SCN separately.
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2. Take 10 mL each of ferric chloride and potassium thiocyanate solution. Blood red colour will be obtained.
3. Take seven test tubes and mark them a tag. Put one mL red solution in each test tube and mark up to
5 mL by adding distilled water into it.
4. Keep the solution in a test tube marked a for comparing its colour with the other solutions.
5. In test tube b, add 1 mL of NH SCN solution and compare the intensity of the blood red colour with
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the solution of test tubes a and b.
6. Repeat the observations with the solutions of the test tubes c, d, e, f and g by adding 2, 3, 4, 5 and
6 mL of NH SCN and FeCl solution separately.
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Observation Table
Test Amount of Amount of FeCl Eff ect on the Eff ect on [Fe(SCN)] 2+ Direction of
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Tube NH SCN solution solution added colour intensity ions concentration the shift of
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added equilibrium
(a)
(b)
(c)
(d)
(e)

(f)
(g)

Precautions
1. The concentration of FeCl and NH SCN should be accurate.
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2. Graduated droppers may be used for adding solution.
3. Comparison of colour of solutions must be done by keeping the reference solutions side by side.

VIVA VOCE

Q1. What is law of mass action?
Ans. ‘Law of mass action’ states the rate at which a chemical substance reacts is directly proportional
to its molar concentration. The rate of chemical reaction is directly proportional to the product of
molar concentration of reactants.
Q2. State the law of chemical equilibrium.
Ans. The ratio of product of molar concentration of products to the product of molar concentration of
reactants raised to the power of their stoichiometric coeffi cients remains constant and this constant
is called equilibrium constant.

Q3. What do you understand by active mass?
Ans. ‘Active mass’ is molar concentration, i.e. in moles per litre of solution.
Q4. What is meant by the statement that chemical equilibrium is dynamic in nature? What is meant by the statement that chemical equilibrium is dynamic in nature?
Ans. The reaction does not stop even after the equilibrium is reached. It still continues, but it appears to The reaction does not stop even after the equilibrium is reached. It still continues, but it appears to
stop because molar concentration of reactants and products become equal.
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