2a- Chemical equilibrium

Question 1

A chemical reaction is said to be in equilibrium when…?

Answer 1

The composition of the reactants and products remains constant indefinitely

Question 2

What does the equilibrium constant (K) characterise?

Answer 2

The equilibrium composition of the reaction mixture

Question 3

What does the value of an equilibrium constant indicate?

Answer 3

The position of equilibrium

Question 4

What units do equilibrium constants have?

Answer 4

They have no units

Question 5

How can the concentrations of pure solids and pure liquids at equilibrium be taken?

Answer 5

As constant and given a value of 1 in the equilibrium expression

Question 6

What does the numerical value of the equilibrium constant depend on?

Answer 6

The reaction temperature (concentration and pressure have no effect)

Question 7

In an exothermic reaction an increase in temperature causes what to happen to the K value and the yield of product?

Answer 7

In an exothermic reaction an increase in temperature causes an increase of the K value and an increase in the yield of product

Question 8

In an endothermic reaction an increase in temperature causes what to happen to the K value and the yield of product?

Answer 8

In an endothermic reaction an increase in temperature causes a decrease in the K value and a decrease in the yield of product

Question 9

What affect does the presence of a catalyst have on the value of the equilibrium constant?

Answer 9

A catalyst has no affect

Question 10

Water is said to be amphoteric, what does this mean?

Answer 10

It can react as both an acid and a base

Question 11

What does the value of the ionic product of water vary with?

Answer 11

Temperature

Question 12

At 25*c what is the approximate value of Kw?

Answer 12

1 x 10^-14

Question 13

In water and aqueous solutions with a pH value of 7, what are the concentrations of both hydronium and hydroxide ions at 25*c?

Answer 13

Concentrations of H3O+ and OH- are both 10^-7 mol/l

Question 14

What do the Bronsted-Lowry definitions of acids and bases state?

Answer 14

An acid is a proton donor and a base is a proton acceptor

Question 15

For every acid there is a…?

Answer 15

Conjugate base which is formed by the loss of a proton

Question 16

For every base there is a…?

Answer 16

Conjugate acid which is formed by the gain of a proton

Question 17

What is a characteristic of strong acids and bases?

Answer 17

Strong acids and bases completely dissociate into ions in aqueous solution

Question 18

What is a characteristic of weak acids and bases?

Answer 18

Weak acids and bases only partially dissociate into their ions in aqueous solution

Question 19

What are three examples of strong acids?

Answer 19

• hydrochloric acid (HCl)
• sulfuric acid (H2SO4)
• nitric acid (HNO3)

Question 20

What are three examples of weak acids?

Answer 20

• carboxylic acids (e.g. ethanoic acid)
• carbonic acid (H2CO3)
• sulfurous acid(H2SO3)

Question 21

What is an example of a strong base?

Answer 21

• solutions of metal hydroxides (except Mg)

Question 22

What are two examples of weak bases?

Answer 22

• ammonia (NH3)

- amines

Question 23

What is the relationship between the Ka value and the strength of the acid?

Answer 23

The smaller the Ka value, the weaker the acid is

Question 24

A soluble salt of a strong acid and a strong base dissolves in water to produce what?

Answer 24

A neutral solution

Question 25

A soluble salt of a strong acid and a weak base dissolves in water to produce what?

Answer 25

An acidic solution

Question 26

A soluble salt of a weak acid and a strong base dissolves in water to produce what?

Answer 26

An alkaline solution

Question 27

What does the name of a salt depend on?

Answer 27

The acid and base used

Question 28

What is a buffer solution?

Answer 28

One in which the pH remains approximately constant when small amounts of acid, base or water are added

Question 29

What is an acidic buffer made with?

Answer 29

A weak acid and the one of its salts made from a strong base

Question 30

What is a basic buffer solution made with?

Answer 30

A weak base and one of its salts

Question 31

What are indicators?

Answer 31

Weak acids which change colour depending on the pH of the solution

Question 32

How is the colour of the indicator determined?

Answer 32

By the ratio of the concentrations of HIn ions to In- ions

Question 33

The colour change is for an indicator is assumed to be distinguishable at what point?

Answer 33

When the concentrations of HIn ions and In- ions differ by a factor of 10

Question 34

How can suitable indicators be selected?

Answer 34

From pH data, including titration curves