11th Class Chemistry Chapter eight Short Questions with Answers Solved

Question: 1

Why do rates of forward reactions slow down the reversible reaction approaches the equilibrium stage?

Answer: 1

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The rate of forward reaction is directly proportional to molar conc.of reactants.Near the equilibrium stage, the concentration of reactant become small .Therefore the rate of forward reaction slow down due to decrease in concentration .

Question: 2

The change of temperature disturbs both the equilibrium position and equilibrium constant of a reaction.Explain with reason?

Answer: 2

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According to Le-Chatelier's principle an increase in temperature will favour the endothermic reaction and decrease in temperature will favour the exothermic reaction.Therefore change of temperature will disturb equilibrium position.The Equilibrium constant is temperature dependent therefore with the change of temperature a new equilibrium a position will be established.

Question: 3

Explain the term reversible reaction and state of equilibrium?

Answer: 3

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State of Equilibrium: The state of reversible reaction in which rate of forward reaction becomes equal to rate of reverse reaction is called chemical equilibrium.There are two types:Static EquilibriumDynamic Equilibrium

Question: 4

Give the physical significance of K_fand K_b?

Answer: 4

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The rate of forward and reverse reaction tell us the condition on which a reaction will depend. It also tells about:

1. Direction of area action

2. Extent of reaction.

Question: 5

State Law of Mass Action?

Answer: 5

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The rate at which substance reacts is directly proportional to its active mass and the rate of reaction is directly proportional to the product of active masses of the reactants.

Question: 6

How K_c predict the extent of chemical reaction?

Answer: 6

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The value of K_c also helps us to predict extent of chemical reaction. There are three possibilities.

1. Large K_cValue: If K_cvalue is large it means reaction is almost completed.

2. Small K_c Value: If K_c value is small amount it means reaction does not proceed appreciably in forward direction. Small amount of product will be formed

3. K_c is in fractions: If K_c is in fractions. It means little forward reaction.

Question: 7

A catalyst does not affect the equilibrium position and K_c of a reversible reaction. Explain ?

Answer: 7

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In most of the reversible reactions, the equilibrium is not always reached within a suitable short time. So an appropriate catalyst is added. A catalyst does not effect the equilibrium position of the reaction. It increases the rates of both forward and backward reactions and it reduces the time to attain the state of equilibrium. Actually a catalyst lowers the energy of activation of both forward and reverse steps by giving new path to the reaction.

Question: 8

Reversible reaction attains the position of equilibrium which is dynamic in nature and not static.Explain it?

Answer: 8

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At Equilibrium state the reaction is not stopped.Only the rate of forward reaction become equal to reverse reaction.Since reaction is in progress in both the direction. Therefore equilibrium is dynamic in nature not static.

Question: 9

Define K_r and K_b for reversible reactions?

Answer: 9

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K_r and K_b: K_f is rate constant for forward reaction and K_b is rate constant for reverse or backward reaction. At equilibrium, rate of forward reaction becomes equal to reverse reaction.

Question: 10

Define state of Dynamic Equilibrium.

Answer: 10

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When the forward and reverse reactions are taking place exactly at the same rate the equilibrium established is called dynamic equilibrium.

Question: 11

Write two application of equilibrium constant?

Answer: 11

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There are following applications of equilibrium constant.

Prediction of direction of reaction.
Extent of a chemical reaction.
Effect of various factors on chemical equilibrium.

Question: 12

Why we need buffer solution?

Answer: 12

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Buffers are the substances which resist the change in pH.Buffers are very important in many areas of chemistry.Buffers are needed in chemical analysis, pharmaceuticals,electroplating etc.

Question: 13

Why the equilibrium constant value has its units for some of the reversible reactions but has not units for some other reactions?

Answer: 13

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Units of K_cdepends upon the number of moles of reactions and products involved in the reaction.

1. If number of moles of reactant and products are same it has no unit.

2. If number of moles of reactants are different from products then K_chas units, related to the concentration or pressure.

Question: 14

Explain the terms buffer and buffer capacity?

Answer: 14

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Buffer: The solution which resist the change in pH by the addition of small amount of an acid or base is called buffer.

Buffer Capacity: The capacity of a buffer to maintain definite pH is called buffer capacity.

Question: 15

State Le-Chatlier's principle?

Answer: 15

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Le-Chatlier's principle:If stress is applied to a system at equilibrium, the system will act in such a way so as to nullify as for as possible the effect of that stress.

Question: 16

Define buffer solution.Give an example of basic buffer?

Answer: 16

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Buffer Solution: The solution that resist in pH changes when small amount of an acid or base is added to it is called buffer solution.It is formed by mixing a weak base and its salt with strong acid.e.g NH₄OH/NH_{4 CI}

Question: 17

Write two uses of buffer solution?

Answer: 17

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The pH of human blood is maintain at 7.35 with the help of buffers.A higher or lower value than this may prove fatal.
Buffers are used in many industrial processes like electroplating, dyes etc.

Question: 18

What will be nature of solution when: (a) pH=3.0 (b) pH=8.0?

Answer: 18

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The value of pH varies between 0-14.A solution having pH value 0-7 are acidic in nature while a solution having pH value 7-14 are basic in nature.

PH= 3 This solution is acidic.
pH= 8 This solution is basic.

Question: 19

What are buffer solutions? How a basis buffer can be prepared?

Answer: 19

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The solution that resists in pH changes when small amount of an acid or a base is added to it is called buffer solution.

Basic buffers are formed by mixing a weak base and its salt with strong acid.Such solution will give basic buffers with pH more than 7.Mixing of NH₄OH and NH₄CI is one of the best example of such a basic buffer.

Question: 20

Define acid and base by Lower-Bronsted concept?

Answer: 20

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Question: 21

A mixture of NH₄OH and NH₄CI gives a basic buffer.Justify the statement ?

Answer: 21

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A buffer which consists of a weak base and its salt with strong acid is called basic buffer.Since NH₄OH is a weak base and NH₄CI is its salt with strong acid.Therefore it is basic buffer.

Question: 22

Is it true that the sum of Pk_aand pK_b is always equal to 14 at all temperature for any acid?

Answer: 22

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It is not true because pK_a and pK_b values are temperature dependent. The degree of ionization of any acid increases as the temperature increases.Hence the value of Pk_aand pK_b change with change in temperature.

Question: 23

Define pH and pOH.Give its equation?

Answer: 23

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pH:The negative logarithm of H⁺ Ions concentration is called pH.

pH = -LOG[H⁺]

pOH:The negative logarithm of OH^- Ions concentration is called pOH.

pOH =-log [OH^-]

Question: 24

What will be nature of solution when (s) pH is more than 7 (b) pH is smaller than 7?

Answer: 24

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pH scale generally ranges from 0 to 14. When pH is less than 7 the solution has acidic nature.When pH is greater than 7 then solution is base.

Question: 25

What are Buffer Solutions?How Acidic Buffers are prepared?

Answer: 25

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Those solution, which resist the change in their pH when a small amount of an acid or a base is added to them, are called buffer solutions.They have specific constant value of pH and their pH values do not change on dilution and on keeping for a long time.

Acidic buffer is prepared by mixing a weak acid and a salt of it with a strong base.Such solution give acidic buffers with pH less than 7.Mixture of acetic acid and sodium acetate is one of the best example of such a buffer.

Question: 26

What are application of buffer in daily life?

Answer: 26

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Buffers are important in many areas of chemistry and allied science like molecular biology, microbiology, cell biology, soil science, nutrition and the clinical analysis.

Question: 27

How can you determine K_sp From solubility?

Answer: 27

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Solubility are given in number of grams of solute per 100g of H₂O .Since density ofH₂O is 1 gcm^-3.Therefore solubility can be written as number of grams of solute/100 cm^-3Of solvent. From the amount of solute/dm³Is calculated.Then amount in grams is converted into moles and using equilibrium K_spCan be calculated.

Question: 28

Differentiate between acidic and basic buffers?

Answer: 28

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The buffer which is prepared by mixing a weak acid and a salt of it with a strong base is known as acidic buffer. Such solutions give acidic buffers with pH less than 7. Mixture of acetic acid and sodium acetate is one of the best example of such a buffer.

The buffer which is prepared by mixing a weak base and a salt of it with a strong acid is known as basic buffer.Such solution give basic buffers with pH more than 7 mixture of NH₄OH and NH_{4CI is one of the best example of basic buffer.}

Question: 29

What will be the nature of solution having pH equal to 12?

Answer: 29

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