C20 Acids, Bases, And pH

Question 1

Define a Bronsted-Lowry acid

Answer 1

Proton donor

Question 2

Define a Bronsted-Lowry base

Answer 2

Proton acceptor

Question 3

What ion causes a solution to become acidic? (2 marks) Name and formula

Answer 3

H+ or more accurately H3O+ as protons react with H2O to form it.

Question 4

What ion causes a solution to be alkaline?

Answer 4

-OH (hydroxide ion)

Question 5

Write the equation for the ionisation of water

Answer 5

2H2O (l) (reversible reaction) H3O+(aq) + -OH(aq)

H2O (l) (reversible reaction) H+(aq) + -OH(aq)

Question 6

Give an example of a monobasic acid.

Answer 6

HCl

Question 7

Give example of a dibasic acid

Answer 7

H2SO4

Question 8

Give an example of a tribasic acid

Answer 8

H3PO4

Question 9

Define a strong acid

Answer 9

An acid that completely dissociates in (aq) to release H+

Question 10

Give examples of strong acids

Answer 10

HCl

H2SO4

HNO3

Question 11

What is the difference between concentrated and strong?

Answer 11

Concentrated means many mol per dm3

Strong refers to amount of dissociation

Question 12

Define weak acid

Answer 12

An acid that only partially dissociates in aq to release H+

Question 13

Give examples of weak acids

Answer 13

Methanoic acid

Any organic acid

Question 14

What is the constant that is used to measure the extent of acid dissociation called?

Answer 14

Acid dissociation constant

Question 15

What is the symbol of acid dissociation constant?

Answer 15

Ka

Question 16

What does a larger Ka value mean?

Answer 16

Larger the Ka - greater the extent of dissociation

Question 17

Write the equation used to convert Ka into pKa.

Answer 17

pKa = -log(Ka)

Question 18

Write the equation used to convert pKa into Ka.

Answer 18

Ka = 10^-pKa

Question 19

What is the relationship between pKa and the strength of the acid?

Answer 19

Smaller the pKa stronger the acid

Question 20

What is the equation used to convert concentration of H+ into pH.

Answer 20

pH = -log[H+]

Question 21

Write the equation used to convert pH into concentration of H+

Answer 21

[H+] = 10^-pH

Question 22

Why is the pH scale useful compared to concentration of H+?

Answer 22

pH scale allows a wide range of H+ concentration to be expressed as simple positive values.

Question 23

What is the relationship between pH and [H+]?

Answer 23

High pH value means a small [H+]

Question 24

If two solutions have a pH difference of 1, what is the difference in [H+]?

Answer 24

A factor of 10

Question 25

[H+] of a strong acid is equal to what?

Answer 25

[H+] = [HA]

Question 26

What is the assumption made when calculating pH of weak acids?

Answer 26

It is assumed that the concentration of acid at equilibrium is equal to the concentration of acid after dissociation. This is because only very little of the acid dissociates.

Question 27

Write the expression for the ionic product of water, Kw

Answer 27

Kw = [H+][OH-]

Question 28

What is the units for Kw?

Answer 28

Mol^2dm^-6

Question 29

What is the value of Kw at 298K?

Answer 29

1.0 x 10^-14

Question 30

What physical factors affect the value of Kw? How do they affect it?

Answer 30

Temperature only - if temperature is increased, the equilibrium moves to the right so Kw increases and the pH of pure water decreases.

Question 31

Indices of [H+] and [OH-] always add up to what value?

Answer 31

-14

Question 32

Define the term strong base

Answer 32

Base that dissociates 100% in water

Question 33

Give examples of strong bases

Answer 33

NaOH KOH Ca(OH)2

Question 34

Give an example of a weak base

Answer 34

Ammonia

Question 35

Write the equation used to calculate [H+] of strong bases

Answer 35

[H+] = Kw / [OH-]

Question 36

Define a salt

Answer 36

The product of a reaction in which the H+ ions from the acid are replaced by metal or ammonium ions. PMT = a compound that is formed when H+ of an ion is replaced by a metal ion or positive ion.

Question 37

What is the definition of Kw?

Answer 37

The temperature dependent constant that represents the dissociation of water into H+ and OH-.

Question 38

Define strength of acids and bases

Answer 38

A measure of the relative degree of dissociation of an acid or base (where strong means complete dissociation and weak means partial dissociation).

Question 39

Define a conjugate acid-base pair

Answer 39

Contains 2 species that can be interconverted by transfer of a proton.

Question 40

Define an alkali

Answer 40

A soluble base that dissociate in aq to release OH-

Question 41

Define a base

Answer 41

An insoluble compound that neutralises an acid to form a salt.

Question 42

Define Ka

Answer 42

The equilibrium constant that shows the extent of dissociation of a weak acid.