Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Physical Chemistry > C21. Acids, Bases and Buffers (A2) (DONE) > Flashcards

C21. Acids, Bases and Buffers (A2) (DONE) Flashcards

1
Q

What is a Brønsted acid and base?

A

A species that donates protons (H+) is a Brønsted acid; A species that accepts protons (H+) is a Brønsted base

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

How do H+ ions exist in water?

A

Form Hydroxonium ions (H3O+)

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

How are hydroxide ions formed?

A

Mix base with H2O, they react with the H+ ions and form hydroxide ions OH-

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

Describe the equation of formation of H3O+ ions

A

HA + H2O <=reversible=> H3O+ + A-

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

Describe the equation of formation of OH- ions.

A

B + H2O <=reversible=> BH(+) + OH(-);

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

Describe the dissociation of bases and acids.

A

Weak bases and acids dissociate poorly; Strong bases and acids dissociate almost completely

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

Describe the reactions of weak acids.

A

Carboxylic acids; Backward reaction favoured, not many H+ produced; CH3COOH <=> Ch3COO(-) + H(+)

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

Describe the reactions of strong acids.

A

HCl, H2SO4, HNO3; Forward reaction favoured strongly, lots of H+ formed; HCl <=> H(+) + Cl(-)

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

Describe the reactions of strong bases.

A

NaOH, KOH; Forward reaction favoured strongly. Lots of OH- ions produced; NaOH <=> Na(+) + OH(-)

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

Describe the reactions of weak bases.

A

NH3; Backwards reaction favoured, not many OH- ions formed; NH3 + H2O <=> NH4(+) + OH(-)

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

Describe a general acid base reaction.

A

HA(aq) + B(aq) <=> BH(+)(aq) + A(-)(aq); (A - acid, B - base); In equilibrium; Protons are exchanged

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

Describe the reaction between acids and water.

A

H2O acts as a base, accepting proton forming hydronium ions, (H3O+); HA(aq) + H2O(l) <=> H3O(+)(aq) + A(-)(aq)

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

Describe the ionic properties of water.

A

Exist in equilibrium; 2H2O <=> H3O(+) + OH(-); Simplified, H2O <=> H(+) + OH(-); H2O dissociates into ions very weakly; Insignificant amount of OH- & H+ compared to H2O molecules;

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

What is the Kc of water?

A

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

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

What is the Kw?

A

Kw = [H+][OH-]; Ionic product of water; Kw = 1 x 10^-14 mol2dm-6

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

What are the factors that affect Kw ?

A

Value of Kw is same in a solution at given temp; Value changes if temp changes;

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

Describe the ionic properties of pure water.

A

Pure H2O has equal conc of H+ and OH- ions; [H+] = [OH-]; Kw = [H+]^2

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

What is pH?

A

Logarithmic scale that measures the concentration of H+ ions in a solution

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

What is the equation to calculate pH?

A

pH = -log10[H+]

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

What is the equation to calculate concentration of H+ ions?

A

[H+] = 10^-pH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How do monoprotic acids behave when dissociating?

A

Dissociate to produce 1 H+ for every acid molecule; Conc of acid = conc of H+ ions; [H+] = [Acid]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How do diprotic acids behave when dissociating?

A

Dissociates to produce 2 H+ ions for every acid molecule; Conc of acid = 2 x conc of H+ ions; 2[H+] = [Acid]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How do you calculate pH of base in aqueous solution?

A

Find [OH-] and Kw of solution at given temperature; Substitute into formula Kw = [H+][OH-]; Find pH using pH = log10[H+]

24
Q

Describe the dissociation of strong bases.

A

Dissociate fully; Strong bases dissociate to produce on OH- for every basic molecule, Base = [OH-] ; NaOH => Na(+) + OH[-]

25
What is Ka?
Acid dissociation constant; Ka = [H+][A-] / [HA] start;
26
What is Ka used for?
Find the constant for the equilibrium for weak acid dissociation; HA <==> H(+) + A(-)
27
What are the assumptions made during Ka calculations?
Small amount of weak acid (HA) dissociates, [HA(aq)] Equilibrium = [HA(aq)] Start; Dissociation of acid is greater than that of water in solution, all H+ ions come from acid, [H+(aq)] = [A-(aq]
28
What's the formula for finding Ka for weak acids?
Ka = [H^2] / [HA]
29
What is pKa?
Method of measuring strength of an acid; Lower the value the stronger the acid; pKa = -log10Ka
30
What does the p in pH mean?
p = -log10; pH = -log10[H+]
31
Whats the equation for finding Ka from pKa?
Ka = 10^-pKa
32
What are titrations used for?
Used to work out the concentration of an acid or base
33
What's the basic method for titrations?
Acid or base of known conc in burette; Have acid or base of unknown conc but known volume in conical flask; Add chemical from burette into conical flask till indicator changes colour; Read how much chemical was added from burette to neutralise; Repeat till 2 concordant results, 0.1cm^3 apart
34
What is the endpoint?
Point at which indicator changes colour
35
What a precautions do you have to take when reading volume form a burette?
Read from bottom of the meniscus
36
Describe a titration graph of a strong acid and strong base
pH starts 1, due to excess strong acid; End around 13pH due to excess strong base; Sharp sigmoid shape
37
Describe a titration graph of a strong acid and weak base.
pH starts 1, due to excess strong acid; Ends around pH 9 due to excess weak base; Sharp sigmoid shape
38
Describe a titration graph of a weak acid and strong base.
Approximately pH 5 start, due to excess weak acid; Ends around pH 13 due to excess strong base; Sharp sigmoid shape
39
Describe a titration graph of a weak acid and weak base?
Approximately pH 5 start, due to excess weak acid; Ends around pH 9, due to excess weak base; Softer sigmoid shape
40
What is the equivalence point?
Acid has been neutralised fully by base; Sharp vertical rise shows rapid change in pH
41
Why are weak acid - weak base titration curves bad examples for showing equivalence points?
Change in pH is small and sigmoid shape is not as well pronounced
42
What is the half neutralisation point?
Point halfway between 0 and the equivalence point; Used to calculate pKa of weak acids by taking pH at this point; At this point [HA] (acid) = [A-] (salt formed)
43
What conditional equation can be formed at half neutralization point?
Ka = [H+]; -logKa = -log[H+]; pKa = pH
44
What factors are needed for indicators to be suitable for the titration?
Indicator must change colour entirely within vertical part of titration; For it to be effective at determining the end point
45
What do you use to measure the endpoint of weak acid - weak base titrations?
pH meter as no sharp pH change
46
Describe a diprotic acid titration graph.
2 separate curves due to protons being released at different times; 2 equivalence points; Stair shaped graph;
47
Give the definition of buffers.
Chemical that resists the change in pH when small amounts of acid or base are added; They do not stop the change in pH, they resist it
48
What are the types of buffers?
Acidic and base buffers
49
What do acidic buffers do and what are they formed from?
Resist the change in pH in order to keep the solution below pH7 7. They are made from a weak acid and its salt
50
How do acidic buffers work?
2 equilibrium equations co-exist in the same beaker; Eq 1, Acid <=> conjugate base + H(+); Weak acid dissociates weakly so eq lies to the left heavily; Eq 2, Salt <=> salt ion + H(+); Salts dissociate strongly so eq lies heavily to the right; When H+ added, reacts with salt ion (high conc of these from salt) from Eq 2 forming acid for Eq 1; Eq shifts to left, more acid produced; OH- added, reacts with H+ ions forming H2O; Low conc of H+ is replenished from high conc of acid to counteract change; Eq shifts to right to replace reacted H+ ions
51
What do basic buffers do and how are they formed?
Resist the change in pH in order to keep the solution above pH7 made from weak base and its salt
52
How do basic buffers work?
2 equilibriums equations coexist in same beaker; Eq 1, Base + H2O <=> Base ion + OH-; Weak base dissociates weakly, little OH- ions maid, eq lies to left; Eq 2, Salt <=> Conjugate base + Conjugate acid; Salt dissociates strongly, eq lies to right; OH- added, reacts with conjugate base from eq2; High conc of these from salt; More base and H2O produced, eq shifted to left; H+ added, reacts with OH- ions; Low conc of OH- but replenished from high conc of base and H2O; Eq shift right
53
How do you calculate the pH of a buffer?
Need to know Ka and concentration of weak acid and salt; Assume [Salt] = [A-] and [HAstart] = [HAequilibrium];
54
What assumptions are made when calculating the pH change of a buffer?
When strong acid added assume all H+ ions react with salt ions [A-], to form acid [HA]; Remember to add volumes together
55
What are the uses of buffers?
Shampoo, pH 5-6; Hair becomes dry and damaged if exposed to alkaline conditions; Washing powder, biological washing powders contain enzymes only work at specific pH; Blood, pH needs to be kept at pH7.4; CO2 plays the role of buffer
56
What is the equation for finding [H+] from pH?
[H+] = 10^-pH

Physical Chemistry (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions