Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry Exams > pH > Flashcards

pH Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What does Kw equal?

A

Kw = [OH-][H+]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the value of Kw at standard conditions?

A

1x10^-14

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do you work out pKw from Kw?

A

pKw = -lg(Kw)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a Bronsted-Lowry acid?

A

Proton donor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a Bronsted-Lowry base?

A

Proton acceptor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the difference between a base and an alkali?

A

Bases that dissolve in water are alkali. All alkalis are bases but not all alkalis are bases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a conjugate base?

A

When an acid donates a proton, the species formed/left over is the conjugate base

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a conjugate acid?

A

When a base accepts a proton, the species formed is the conjugate acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How do we work out the pH of strong acids?

A

pH = -lg [H+]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is Ka?

A

The acid dissociation constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What assumption is made in the calculation of Ka?

A

The concentration of both dissociation products is the same

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the equation for finding Ka?

A

[H+]^2 / [HA] = Ka

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

If we are given the value of Ka and the concentration of the weak acid, how can we work out the pH?

A

Conc of acid x Ka = [H+]^2
Square root to get [H+]
-lg x [H+] = pH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is H2SO4 an example of?

A

A diprotic acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is a diprotic acid?

A

An acid that when it dissociates releases 2 H+ ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do you work out the concentration of H+ from pH?

A

10^-pH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How do you work out pKa?

A

pKa = -lg (Ka

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do you work out Ka from pKa?

A

Ka = 10^-pKa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What must you use to work out the pH of a base?

A

Kw

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How do you use Kw to find the pH of a base?

A

Once you find [OH-]:

Kw / [OH-] = [H+]

21
Q

Why is it difficult to find the end point of a titration between a weak acid and a weak base?

A

Because the starting and finishing pH are close together, making it difficult to identify an end point.

22
Q

How do you pick an indicator for your titration?

A

You must pick an indicator that changes colour at a pH within the end point

23
Q

What is the pH range of methyl orange?

A

3.1-4.4

24
Q

What is the pH range of phenolphthalein?

A

8.2-10

25
Q

What is the colour change for phenolphthalein acid -> alkali?

A

Colourless -> Pink

26
Q

What is the colour change for methyl orange acid -> alkali?

A

Red -> Yellow

27
Q

What indicator should be used for strong acid-strong base titrations?

A

Phenolphthalein or methyl orange can be used

28
Q

What indicator should be used for weak acid-strong base titrations?

A

Phenolphthalein

29
Q

What indicator should be used for strong acid-weak base titrations?

A

Methyl orange

30
Q

What is the end point of a titration on a graph?

A

The steep section

31
Q

What is a buffer?

A

A buffer solution is one which resists changes in pH when small quantities of an acid or an alkali are added to it

32
Q

What are acid buffers?

A

Buffers with a pH below 7

33
Q

What are alkaline buffers?

A

Buffers with a pH above 7

34
Q

How are acidic buffers made?

A

Acidic buffer solutions are commonly made from a weak acid and a salt of its conjugate base

35
Q

What is the common example of an acidic buffer?

A

A mixture of ethanoic acid and sodium ethanoate in solution

36
Q

How are alkaline buffers made?

A

Alkaline buffers are commonly made from a weak base and a salt of its conjugate acid

37
Q

What is the common example of an alkaline buffer?

A

A mixture of ammonia solution and ammonium chloride solution.

38
Q

What 2 assumptions are made when calculating the pH of an acidic buffer made up of carboxylic acid and sodium ethanoate?

A

The weak carboxylic acid doesn’t dissociate (so initial conc remains the same)
The sodium ethanoate (salt) dissociates fully (so conc of salt = conc of ethanoate ion)

39
Q

What is the buffer range in a titration?

A

The part of a titration where changes in pH is slow and gradual

40
Q

What happens if you add H+ to an acidic buffer (e.g. ethanoic acid + sodium ethanoate)?

A

The H+ will react with the carboxylate ion (CH3COO-) to form more carboxylic acid (CH3COOH)

41
Q

What if you add OH- to an acidic buffer (e.g. ethanoic acid + sodium ethanoate)?

A

The OH- will react with H+ ions, and the CH3COOH will counteract this change by dissociating more and producing more H+ ions (le Chatelier’s principle)

42
Q

How else can you make an acidic buffer (without a salt)?

A

Acidic buffers can be made from mixing an EXCESS of a weak acid with a strong base

43
Q

What is the Henderson-Hasselbalch equation?

A

pH = pKa + lg (salt/acid)

44
Q

What is the effect of a ten-fold dilution on a strong acid?

A

pH increases by one for each 10-fold dilution
1 moldm-3 = pH 0
0.1 moldm-3 = pH 1
0.01 moldm-3 = pH 2

45
Q

What is the effect of a ten-fold dilution on a weak acid?

A

pH increases by 0.5 for each 10-fold dilution
1 moldm-3 = pH 2.38
0.1 moldm-3 = pH 3.88
0.01 moldm-3 = pH 3.38

46
Q

What is the half neutralisation point?

A

The point of a titration at which half of the acid has been neutralised

47
Q

At the half neutralisation point, what do we know about the concentrations of the acid and conjugate salt?

A

The conc of the acid = the conc of the salt

Half of the acid has been neutralised to the salt

48
Q

What can we work out from pH at the half neutralisation point?

A

At the half neutralisation point, pH = pKa

49
Q

Why does pH = pKa at the half neutralisation point?

A

Henderson’s equation is pH = pKa + log(salt/acid)
The conc of the salt and the acid is the same, so salt/acid = 1
log(1) = 0
So essentially the equation is pH = pKa + 0

Chemistry Exams (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions