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A level Chemistry > Acids, Bases and Buffers > Flashcards

Acids, Bases and Buffers Flashcards

1
Q

What is an acid?

A

proton donors

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2
Q

What is a base?

A

proton acceptors

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3
Q

The definitions we use for acids and bases are called

A

Bronsted Lowry acids and bases

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4
Q

oxonium ion?

A

H3O+ - H2O forms a dative covalent bond to H+

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5
Q

when acids dissociate?

A

(x)H+ + negative ion always forms

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6
Q

When a monoprotic acid dissociates?

A

1 (mol) of H+ forms

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7
Q

When a diprotic acid dissociates?

A

2 H+ form

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8
Q

When a triprotic acid dissociates?

A

3 H+ form

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9
Q

Idm if acid is di/triprotic, when it dissociates how many moles of the salt forms?

A

1 mole

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10
Q

could say ? instead of protic

A

basic

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11
Q

Acid base pairs?

A
  • involves 2 acid base pairs

* 2 particles that change into each other by losing/ gaining a H+

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12
Q

ABP: what does the acid form?

A

Conjugate base by donating a H+

the CB has a negative charge

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13
Q

ABP: what does the base form?

A

Conjugate acid.

the CA has a positive charge

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14
Q

water is amphoteric meaning?

A

can act as acids and bases

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15
Q

strong acid definition?

A

Fully dissociate into H+ e.g. HCl

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16
Q

weak acid definition?

A

only partially dissociate into H+

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17
Q

conc acid definition?

A

high no. of moles per dm3

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18
Q

dilute acid definition?

A

fewer moles per dm3

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19
Q

for the reaction to be a neutraliation?

A

water must be formed, so metal + acid is not a neutralisation

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20
Q

⭐ionic equations

A

only include ions that change e.g. state

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21
Q

pH equation?

A

-log [H+]

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22
Q

[H+] =

A

10 to the power of -pH

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23
Q

calc pH of strong acid?

A

• in strong acid, all H+ dissociate so [H+] dissociated = [H+] in acid

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24
Q

give pH to?

A

2dp

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25
calc pH of di/triprotic acid?
x the [H+] by 2/3 b4 putting in pH equation
26
What is Kw used for?
* the ionic product of water, 10^-14mol2dm-6 at 298K | * used to find the pH of alkaline solutions
27
Kw equation?
Kw/ [OH-] = [H+]
28
when do u use Kw?
when the [OH-] is given, get [H+] and then calc pH
29
why does an increase in T change the pH of water?
• endo forwards reaction favoured, eq shifts to the right • [H+] inc so pH ⬇
30
remember that lower pH =
more acidic
31
to calc pH of weak acids?
DIFFERENT METHOD - can't just use [acid] as [H+]
32
neutral solution =
equal conc of H+ and OH- - does not have to be at pH 7
33
when 2x OH in the alkali?
times the [OH-] by 2
34
dissociation of a weak acid is?
reversible
35
Ka =
* the acid dissociation constant * larger the Ka value, the stronger the acid - eq lies towards products * Units = moldm-3
36
Ka equation?
Ka = [H+][A-] / [HA] simplified to Ka = [H+]2/ [HA]
37
Ka (in relation to pKa)?
Ka =10-^pKa
38
10 is not just 10 it's...
shift log
39
pKa =
pKa = -logKa | think of Ka like [H+]
40
the stronger the acid, the lower the?
pKa value
41
3 steps to calculating the pH of a weak acid?
1. get Ka if pKa given 2. get [H+] 3. get pH
42
weak acid: depending on the no. of marks,
show the rearranging of the Ka equation
43
how can u tell if an acid is weak?
must be given Ka or pKa
44
relationship between pH and [H+]
as pH ⬇, [H+] ⬆
45
relationship between pKa and Ka?
as pKa ⬇, [Ka] ⬆ same relationship as pH and [H+]
46
What is a bufffer?
* solution that can resist a change in pH when small amounts of acid or base are added * can be acidic or basic
47
What do buffer contain?
• a weak acid and a large amount of a salt of a strong base | e.g. ethanoic acid and sodium ethanoate - G1 metals used cos soluble
48
What's the point of the salt of a strong base?
forms the same negative ion as the acid when the acid dissociates. creates a reserve
49
What happens to a buffer when H+ are added?
* equilibrium shifts to the left * uses up H+ * we'd run out of the negative ion * but bc of the salt, there's a reserve of negative ions and pH doesn't change
50
if OH- are added to the buffer solution?
* would react w H+, reducing H+ so eq would shift to the right inc amount of H+ * not gonna run out of acid bc it's weak so only a small amount has ionised - lots left * this is why weak acid is used * pH doesn't change salt not involved here
51
why can we used the moles instead of conc to calc Ka of buffer solution?
bc all solutions are in the same total V so conc ratio = moles ratio
52
for buffers don't ⭐
simplify [H+][A-} to [H+]2
53
buffers work out?
moles of both then do Ka
54
If acid added to buffer?
amount of acid inc and salt decreases by that amount of moles
55
If you want an buffer of a specific pH the choose a an acid of a similar ?
pKa value
56
3 factors that influence pH?
Ka, [acid], [base]
57
What is the most important factor that determines the pH of a buffer?
Ka/ pKa
58
what can alter the pH of a buffer solution?
ratio of acid to salt
59
how is the pH of a buffer affected by dilution?
not diluted, Salt and acid are in the same container so the ratio of them doesn't change - stays constant and so pH doesn't change
60
Weak acid weak base indicator?
unclear where the equivalence point is so diff to select an indicator
61
indicator pHs?
over 7: P | under 7: methyl orange
62
equivalence point?
[H+] = [OH-]
63
What can be done from an acid base/ graph?
read pH and calc [H+]
64
strong acid and strong base equivalence point at?
ph 7
65
For an indicator to work in a titration?
the range of the indicator's colour change must be within the range of the pH change at the equivalence point

A level Chemistry (39 decks)

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