CH21 Acids and Bases

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 be acidic

Answer 3

H+ ion or H3O+ (oxonium) ion, as protons react with water to form oxonium

Question 4

What ion causes a solution to be alkaline

Answer 4

-OH ion

Question 5

Ionisation of water

Answer 5

2H2O ⇌ H3O+ + -OH

H2O ⇌ H+ + -OH

Question 6

Kw equation

Answer 6

Kw = [H+][OH-]

Question 7

Value of Kw at 298K

Answer 7

1.0 x 10˄-14

Question 8

Physical factor which affects Kw

Answer 8

Temperature - equilibrium shifts right if there is an increase in temperature so Kw increases and pH of pure water decreases

Question 9

Why is pure water still neutral, even if pH does not equal 7

Answer 9

[H+] = [OH-]

Question 10

Expression for pH in terms of H+

Answer 10

pH = -log10 [H+]

Question 11

Relationship between pH and concentration of H+

Answer 11

Lower pH = higher concentration of H+

Question 12

If 2 solutions have a pH difference of 1, what is their difference in [H+]

Answer 12

A factor of 10

Question 13

How do you find [H+] from pH

Answer 13

[H+] = 10˄-pH

Question 14

How do you find [OH-] from pH at 298K

Answer 14

Find [H+]
Use Kw - 1x10˄-14
Calculate [OH-}

Question 15

Difference between finding [H+] from the concentration of diprotic and triprotic acids

Answer 15

need to multiply the concentration of acid by the number of protons to find [H+]

Question 16

How do you calculate the pH of a strong alkaline solution

Answer 16

Use Kw to calculate [H+] from [OH-]

Use pH = -log[H+]

Question 17

Define term strong acid

Answer 17

One which fully dissociates in water

Question 18

Define the term strong base

Answer 18

One which fully dissociates in warer

Question 19

Difference between concentrated and strong

Answer 19

Concentrated means may mol per dm3

Strong refers to amount of dissociation

Question 20

What is a weak acid and weak base

Answer 20

Do not fully dissociate in water.

Only partially dissociate into their ions

Question 21

Examples of strong acids

Answer 21

HCl
H2SO4
H3PO4

Question 22

Examples of strong bases

Answer 22

NaOH
CaCO3
Na2CO3

Question 23

Examples of weak acids

Answer 23

CH3COOH

Question 24

Examples of weak bases

Answer 24

NH3

Question 25

Expression for Ka (strong acid)

Answer 25

Ka = [H+][A-] / [HA]

Question 26

How to work out pH of a weak acid

Answer 26

Use Ka - substitute values [A-] and [HA] | Use pH = -log[H+]

Question 27

What is a titration

Answer 27

The addition of an acid/base of known titration to a base/acid of unknown titration to determine its concentration

Question 28

Define equivalence point

Answer 28

The point at which the exact volume of base has been added to just neutralise the acid

Question 29

What generally happens to pH of solution around equivalence point

Answer 29

Large and rapid change in pH, except in weak-weak titration

Question 30

How to calculate conc of a reactant if volume of it and volume and conc of other reactant are known

Answer 30

Calc mol of one reactant USe balanced equation USe cone = mol/vol to calculate conc

Question 31

What is the end point

Answer 31

The volume of acid or alkali added when the indicator just changes colour. If right indicator is chosen - equivalence point = end point

Question 32

Properties of a good indicator

Answer 32

Sharp colour change End point same as equivalence point Distinct colour change

Question 33

Indicator used for strong acid - strong base titration

Answer 33

Phenopthalein or methyl orange

Question 34

Indicator used for strong acid-weak base titration

Answer 34

Methyl orange

Question 35

Indicator used for weak acid - strong base titration

Answer 35

Phenolpthalein

Question 36

Indicator used for weak acid - weak base titration

Answer 36

Neither methyl orange or phenolpthalein as neither give sharp change at end point

Question 37

Colour of methyl orange in acid and alkali. What pH does it change at

Answer 37

Acid: Red Alkali: Yellow Changes at 4-5 pH

Question 38

Colour of phenolpthalein in acid and alkali. What pH does it change at

Answer 38

Acid: Colourless Alkali: Red Changes at 9-10 pH

Question 39

What is the half-neutralisation point

Answer 39

When volume = half the volume that has been added at the equivalence point

Question 40

Define a buffer solution

Answer 40

A solution that can resist changes in pH when small amount of acid / alkali are added

Question 41

What do acidic buffer solution contain

Answer 41

A weak acid and a soluble salt of that acid that fully dissociates

Question 42

Reaction of acidic buffer with added acid

Answer 42

A- + H+ --> HA | opposes addition of H+

Question 43

Reaction for acidic buffer with added alkali

Answer 43

HA + OH- --> H20 + A-

Question 44

How else can an acidic buffer solution be made

Answer 44

Neutralise half of a weak acid with an alkali | Forms a weak acid / soluble salt mixture

Question 45

What do basic buffer solutions contain

Answer 45

Weak base and a soluble salt of that weak base

Question 46

How to calculate pH of buffer solutions

Answer 46

Use Ka of weak acid Calculate [H+] Calculate pH

Question 47

How to calculate new pH of buffer solution when acid or base is added

Answer 47

Calc number of mol of H+ and A - and HA before addition of acid or base Work out new mol of A- and HA Find [H+] Calculate pH