Acids And Bases

Question 1

What is a Bronsted-Lowry acid

Answer 1

A proton donor

Question 2

What is a bronsted-lowery base

Answer 2

A proton acceptor

Question 3

What does bronsted Lowry refer to

Answer 3

Exchange of protons

Question 4

What is pH

Answer 4

-log10 /H+/

Question 5

What is a strong acid

Answer 5

Strong acids fully dissociate in water

Question 6

What assumption can be made when calculating pH of a strong acid

Answer 6

The concentration of hydrogen ions in a MONOPROTIC acid is the SAME as the concentration of the acid

Question 7

How many decimal places is pH measured to

Answer 7

2 d.p.

Question 8

How do you find /H+/ from pH

Answer 8

/H+/ = 1 x 10^-pH

Question 9

What is equilibrium for water

Answer 9

H2O <=> H+ (aq) + OH- (aq)

Question 10

What is the equilibrium expression for water

Answer 10

Kc = /H+/ /OH-/
/H2O/

Question 11

What can the equilibrium expressions for water be simplified to

Answer 11

Kw = /H+/ /OH-/

Question 12

Why can the equilibrium expression for water be simplied

Answer 12

Pure water doesn’t dissociate much so we assume the concentrations stays constant, so isn’t included in Kw expression

Question 13

What is the kw for water

Answer 13

At 25 degrees c, Kw = 1 x 10^-14 mol2dm-6

Question 14

What can we assume for pure water or neutral solutions

Answer 14

/H+/ = /OH-/

Question 15

What can the equilibrium expression be simplified to when solution is neutral

Answer 15

Kw = /H+/^2

Question 16

When does Kw change

Answer 16

At different temperatures

Question 17

Why does Kw change with temperature

Answer 17

Position of equilibrium changes, so /H+/ changes, so pH changes

Question 18

What is the concentration of a strong base equal to

Answer 18

/OH-/

Question 19

What are the steps to calculating the pH of a strong base

Answer 19

1) Find /H+/ using the Kw expression
2) pH = -log10 /H+/

Question 20

Describe a weak acid

Answer 20

An acid that doesn’t fully dissociate

Question 21

What is the equilibrium equation for weak acids

Answer 21

HA + H2O <=> H3O + A-

Question 22

What does the equilibrium equation for weak acids simplify to

Answer 22

HA <=> H+ + A-

Question 23

What is the weak acids dissociation expression

Answer 23

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

Question 24

What does a larger Ka value mean

Answer 24

Stronger acid

Question 25

What can the weak acid equilibrium expression be simplified to

Answer 25

Ka = /H+/^2 /HA/inital

Question 26

What are the assumptions made to simplify the weak acids equilibrium expression

Answer 26

1) /H+/ = /A-/ as they dissociate in a 1:1 ration 2) amount of dissociation is small, so assume that initial concentration of undissociated acid remains constant

Question 27

How do you work out pH of a weak acid

Answer 27

PKa = -log10 (Ka)

Question 28

How do you work out Ka from pKa

Answer 28

Ka = 1 x10^ -pKa

Question 29

What are the steps to work out a strong acid + strong base neutralisation

Answer 29

1) work out the moles of acid and base 2) work out which (acid or base) is in excess

Question 30

What is the next step of strong acid + strong base neutralisation if ACID IS IN EXCESS

Answer 30

3) /H+/ = moles excess H+ / total volume 4) pH = -log10 /H+/

Question 31

What is the next step of strong acid + strong base neutralisation IF BASE IS IN EXCESS

Answer 31

3) /OH-/ = moles excess OH- / total volume 4) /H+/ = Kw / /OH-/ 5) pH = -log10 /H+/

Question 32

What do you do in a neutralisation calculation if a diprotic acid is used

Answer 32

Multiply moles x 2

Question 33

What are the steps for a weak acid, strong base neutralisation calculation

Answer 33

1) work out moles of acid and base 2) If excess acid, work out new concentration of HA 3) work out concentration of salt /A-/ formed 4) rearrange Ka expression for /H+/ 5) pH = -log10 /H+/

Question 34

How to work out new concentration of HA if excess acid (Weak acid, strong base neutralisation)

Answer 34

/HA/ = inital moles HA - moles OH- / total volume

Question 35

How to work out concentration of salt /A-/ formed (Weak acid, strong base neutralisation)

Answer 35

/A-/ = moles OH- added / total volume

Question 36

When can Ka expression simplify further

Answer 36

Weak acid reacts with exactly half the neutralisation volume of alkali

Question 37

What is assumed when Ka is simplified at half neutralisation

Answer 37

/HA/ = /A-/

Question 38

What does the Ka expression simplify to at half neutralisation

Answer 38

Ka = /H+/

Question 39

What does pH equal at half neutralisation

Answer 39

PH = pKa

Question 40

In questions, what is the volume of alkali equal to

Answer 40

Half acid volume

Question 41

How to calculate pH of a diluted strong acid

Answer 41

/H+/ = /H+/old x old volume New volume

Question 42

How to calculate pH of a diluted base

Answer 42

/OH-/ = /OH-/old x Old volume New volume /H+/ = Kw /OH-/

Question 43

On a titration curve, where is the buffer region

Answer 43

When the graph horizontally plateaus

Question 44

Define a buffer solution

Answer 44

One where the pH does not change significantly when small amounts of acid o alkali are added to it

Question 45

How to make a basic buffer

Answer 45

Weak base and a salt of that weak base

Question 46

How do you make the salt of a weak base

Answer 46

React weak base with strong acid

Question 47

How do you make an acidic buffer

Answer 47

Weak acid and a salt of that weak acid

Question 48

How do you make the salt of a weak acid

Answer 48

React weak acid with strong base

Question 49

Give an example of components of an acidic buffer

Answer 49

Ethanoic acid and sodium ethanoate

Question 50

Give an example of components of a basic buffer

Answer 50

Ammonia and ammonium chloride

Question 51

What does a buffer contain a reservoir of

Answer 51

Reservoir of HA and A- ions

Question 52

What is the equilibrium equation for an acidic buffer

Answer 52

Acid <=> conjugate base + /H+/

Question 53

What happens to equilibrium if small amounts of acid are added to an acidic buffer

Answer 53

Equilibrium shifts to the left, removing nearly all H+ ions added

Question 54

Why does pH stay constant when acid is added to acidic buffer

Answer 54

There’s a large concentration of the salt ion in the buffer, so ratio of acid to conjugate base remain constant

Question 55

What forms when small amounts of alkali are added to an acidic buffer

Answer 55

The OH- ions react with H+ ions to form water

Question 56

What happens to the position of equilibrium when alkali is added to acidic buffer

Answer 56

Equilibrium shifts right to produce more H+ ions

Question 57

Suggest a way salt content can be added to a buffer

Answer 57

Solid salt or salt solution could be added

Question 58

What values can you use instead of concentration when making a buffer by adding solid salt

Answer 58

The mole values of HA and A- as they have the same new final volume

Question 59

How does adding a small amount of alkali to buffer affect moles

Answer 59

Increase moles of alkali by number added Decrease moles of acid by number added Find new concentrations using these new values for moles

Question 60

What happens to moles when small amount of acid is added to buffer

Answer 60

Increase moles of acid by number added Decrease moles of alkali by number added Find new concentrations using these new values for moles

Question 61

How will diluting a buffer solution affect pH

Answer 61

Diluting with water wont change the ph

Question 62

Why does diluting buffer with water not change its pH

Answer 62

The ratio of HA to A- stays constant as both diluted by same proportion