Acids And Bases

Question 1

Define a Brønsted-Lowry acid

Answer 1

Proton donor

Question 2

Define a Brønsted-Lowry base

Answer 2

Protons acceptor

Question 3

What ion causes a solution to be acidic

Name and formula

Answer 3

H+ or more accurately H3O+ (Oxonium ion) as protons react with H2O to form it

Question 4

What ion causes a solution to be alkaline

Answer 4

-OH

Question 5

Write an equation for the ionisation of water

Answer 5

2H2O H3O+ + -OH

H2O H+ + -OH

Question 6

Derive Kw using the equation for the ionisation is water

Answer 6

Kc = [H+] [OH-]
[H2O]

As [H2O] is so large compared to the other concentrations the concentration can be considered to be constant

Kw = [H+] [ OH-]

Question 7

What is the value of Kw at 298K

Answer 7

1 x 10^-14

Question 8

What physical factors affect the value of Kw

How do the affect it

Answer 8

Temperature - if temperature is increased the equilibrium moves to the right so Kw increases and the 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

Give an expression for pH in terms of H+

Answer 10

pH = -log10[H+]

Question 11

What is the relationship between pH and concentration of H+

Answer 11

Lower pH the higher the concentration of H+

Question 12

Of two solutions have a pH different of 1 what is the difference in [H+]

Answer 12

X10

Question 13

How do you find [H+] from pH

Answer 13

10^-pH

Question 14

How do you find [OH-] from pH in standard conditions

Answer 14

Find [H+] use Kw to calculate [OH-]

Question 15

What is the different when finding [H+] from the concentration of diprotic and triprotic acids

Answer 15

Need to multiply the concentration of the 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 the 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 water

Question 19

What is the difference between concentrated and strong

Answer 19

Concentrated means many mil per dm3

Strong refers t amount of dissociation

Question 20

What is a weak acid and a weak base

Answer 20

Weak acids and bases do not fully dissociate in water

They 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

Any organic acid

Question 24

Examples of weak bases

Answer 24

NH3

Question 25

What is Ka

Answer 25

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

Question 26

How would you work out the pH of a weak acid

Answer 26

Use Ka | Then 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 the concentration An indicator is used to show that neutralisation has occurred or a pH meter

Question 28

Describe titration curve for strong acid with a strong base

Answer 28

High Gradually decrease Quick decrease then levels off

Question 29

Titration for a strong acid with a weak base

Answer 29

pH of about 9 Slight decrease Quick decrease Levels off

Question 30

Titration curve for a weak acid with weak base

Answer 30

``` Ph of about 9 Slight decrease Slight increase Quick decrease Levels off ```

Question 31

Titration curve for a weak acid and strong base

Answer 31

High pH Levels off Quick decrease Levels off

Question 32

Define equivalence point

Answer 32

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

Question 33

What generally happens to the pH of the solution around the equivalence point

Answer 33

There is a large and rapid change in pH

Question 34

What is the end point

Answer 34

The boiling of acid or alkali added when the indicator changes colour If the right indicator is chosen then the equivalence point = end point

Question 35

What are the properties of a good indicator

Answer 35

Sharp colour Change End point list be the same as the equivalence point Distinct colour change

Question 36

What indicator would you use for a strong acid base titration

Answer 36

Phenolphthalein

Question 37

What indicator would you use a strong acid weak base titration

Answer 37

Methyl orange

Question 38

What indicator would you use for a weak acid and strong base titration

Answer 38

Phenolphthalein

Question 39

What indicator would you use for a weak acid weak base titration

Answer 39

Neither methyl orange or phenolphthalein

Question 40

Methyl orange

Answer 40

Red in acid Yellow in alkali Changed at pH 4-5

Question 41

Phenolphthalein

Answer 41

Colourless in acid Red in alkali Changes at pH 9-10

Question 42

What is the half neutralisation point

Answer 42

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

Question 43

Define a buffer solution

Answer 43

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

Question 44

What do acidic buffer solutions contain in general

Answer 44

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

Question 45

Equation for an acidic buffer with added acid

Answer 45

A- + H+ -> HA

Question 46

Equation for acidic buffer with added alkali

Answer 46

HA + OH- -> H2O + A-

Question 47

What do basic buffer solutions contain in general terms

Answer 47

Weak base and soluble salt of that weak base

Question 48

How can you calculate the pH of buffer solutions

Answer 48

Ka of weak acid | pH = -log[H+]

Question 49

Which buffer system maintains blood pH

Answer 49

H+ + HCO3- CO2 + H2O