chemistry - unit 2.1

Question 1

When is a chemical reaction in equilibrium?

Answer 1

When 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 does an equilibrium constant have?

Answer 4

No units.

Question 5

What are the concentration of pure solids and pure liquids at equilibrium taken as?

Answer 5

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 and is independent of concentration and/ or pressure.

Question 7

For endothermic reactions, what does a rise in temperature cause?

Answer 7

An increase in K and the yield of the product is increased.

Question 8

For exothermic reactions, what does a rise in temperature cause?

Answer 8

A decrease in K and the yield of the product is decreased.

Question 9

What does the presence of a catalyst do?

Answer 9

It does not affect the value of the equilibrium constant.

Question 10

In water and aqueous solutions, where is there an equilibrium?

Answer 10

Between the water molecules and hydronium and hydroxide ions.

Question 11

How can this ionisation of water be represented by?

Answer 11

H2O(l) + H2O(l ) -> H3O+ (aq) + OH− (aq)

Question 12

What does H3O+(aq) represent?

Answer 12

A hydronium ion, a hydrated proton. A shorthand representation of H3O+ (aq) is H+ (aq).

Question 13

What is water?

Answer 13

Amphoteric (can react as an acid and a base).

Question 14

What is the dissociation constant for the ionisation of water known as the ionic product, Kw?

Answer 14

Kw = [H3O+][OH-]

Question 15

What does the value of the ionic product vary with?

Answer 15

Temperature.

Question 16

At 25°C, what is the value of Kw?

Answer 16

approximately 1 × 10-14.

Question 17

What is the relationship between pH and the hydrogen ion concentration given by?

Answer 17

pH=−log[H3O+] and [H3O+] = 10−pH

Question 18

In water and aqueous solutions with a pH value of 7, what are the concentrations of H3O+ (aq) and OH− (aq)?

Answer 18

They are both 10-7 mol l-1 at 25°C.

Question 19

If the concentration of H3O+ (aq) or the concentration of OH− (aq) is known, what can be calculated?

Answer 19

The concentration of the other ion using
Kw or by using pH + pOH = 14 .

Question 20

What is the Brønsted-Lowry definition of an acid?

Answer 20

A proton donor.

Question 21

What is the Brønsted-Lowry definition of a base?

Answer 21

A proton acceptor.

Question 22

For every acid, what is there?

Answer 22

A conjugate base, formed by the loss of a proton.

Question 23

For every base, what is there?

Answer 23

A conjugate acid, formed by the gain of a proton.

Question 24

What are strong acids and strong bases?

Answer 24

Completely dissociated into ions in aqueous solution.

Question 25

What are weak acids and weak bases?

Answer 25

Only partially dissociated into ions in aqueous solution.

Question 26

What are examples of strong acids?

Answer 26

Hydrochloric acid, sulfuric acid and nitric acid.

Question 27

What are examples of weak acids?

Answer 27

Ethanoic acid, carbonic acid and sulphurous acid.

Question 28

What are strong bases?

Answer 28

Solutions of metal hydroxides.

Question 29

What are examples of weak bases?

Answer 29

Ammonia and amines.

Question 30

What can the weakly acidic nature of solutions of carboxylic acids, sulfur dioxide and carbon dioxide be explained by?

Answer 30

Reference to equations showing the equilibria.

Question 31

What can the weakly alkaline nature of a solution of ammonia or amines be explained by?

Answer 31

Reference to an equation showing the equilibrium.

Question 32

What do equimolar solutions of weak and strong acids (or bases) have?

Answer 32

Different pH values, conductivity, and reaction rates, but the stoichiometry of reactions are the same.

Question 33

What is the acid dissociation constant represented by Ka?

Answer 33

[H3O+][A-] / [HA] or pKa where pKa =−log10(Ka)

Question 34

How can the approximate pH of a weak acid be calculated?

Answer 34

Using pH=1/2pKa −1/2log10(c)

Question 35

What does a soluble salt of a strong acid and a strong base dissolve in water to produce?

Answer 35

A neutral solution.

Question 36

What does a soluble salt of a weak acid and a strong base dissolve in water to produce?

Answer 36

An alkaline solution.

Question 37

What does a soluble salt of a strong acid and a weak base dissolve in water to produce?

Answer 37

An acidic solution.

Question 38

What does the name of the salt produced depend on?

Answer 38

The acid and base used.

Question 39

How can the changes in concentrations of H O+ and OH− ions of salt solutions be explained?

Answer 39

Using the appropriate equilibria.

Question 40

What is a buffer solution?

Answer 40

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

Question 41

What does an acid buffer consist of?

Answer 41

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

Question 42

In an acid buffer solution, what does the weak acid provide?

Answer 42

Hydrogen ions when these are removed by the addition of a small amount of base.

Question 43

What does the salt of the weak acid provide, in an acid buffer?

Answer 43

The conjugate bae, which can absorb excess hydrogen ions produced by the addition of a small amount of acid.

Question 44

What does a basic buffer consist of?

Answer 44

A solution of a weak base and one of its salts.

Question 45

In a basic buffer solution, what does the weak base do?

Answer 45

It removes excess hydrogen ions.

Question 46

In a basic buffer solution, what does the conjugate acid provided by the salt do?

Answer 46

it supplies hydrogen ions when these are removed.

Question 47

How can an approximate pH of an acid buffer solution be calculated?

Answer 47

From its composition and from the acid dissociation constant: pH = pKa − log[acid]/[salt]

Question 48

What are indicators?

Answer 48

Weak acids for which the dissociation can be represented as: HIn(aq)+H2O(l) -> H3O(aq) + In-(aq)

Question 49

In aqueous solution, what is the colour of an acid indicator?

Answer 49

Distinctly different from that of its conjugate base.

Question 50

What is the colour of the indicator determined by?

Answer 50

The ratio of [HIn] to [In−]

Question 51

What is the theoretical point at which colour change occurs?

Answer 51

When [H3O+]=Kln.

Question 52

When is the colour change assumed to be distinguishable?

Answer 52

When [HIn] and [In−] differ by a factor of 10.

Question 53

What is the pH range over which a colour change occurs estimated by?

Answer 53

The expression: pH = pKIn +/-1

Question 54

Where can suitable indicators be selected from?

Answer 54

pH data, including titration curves.