Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

A Level Chemistry > Acids And Bases > Flashcards

Acids And Bases Flashcards

1
Q

What is the Brønsted-Lowry definition of

a) an acid
b) a base

A

a) A proton donor

b) A proton acceptor

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

What does monoprotic mean

A

It donates 1 H+ per molecule

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

What does diprotic mean

A

It donates 2 H+ ions per molecule

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

What do strong acids and bases do

A

Completely dissociate

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

What equilibrium is set up when a weak acid dissolves in water

A

HA + H2O (equilibrium) H3O+ + A-

Or

HA (equilibrium) H+ + A-

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

Give the equation of NH3 (weak base) dissolving in H2O

A

NH3 + H2O (equilibrium) NH4+ + OH-

Or

NH3 + H+ (equilibrium) NH4

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

The weaker the base the ____ it dissociates and the more the equilibrium lies to the _____

A

Less

Left

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

Does water act as an acid or a base? What is this called

A

Both

Amphoteric (acts as both an acid and base)

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

Definition of pH

A

pH= -log[H+]

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

As the concentration of H+ increases, what happens to the pH

A

pH decreases

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

To what precision is pH given to

A

2 d.p.

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

Equation to convert pH to [H+]

A

[H+]=10^-pH

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

When converting from H2SO4 to H+ do you divide or multiply by 2

A

Multiply

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

What does Kw=

A

[H+][OH-]

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

What is Kw at 298K/ 25 degrees Celsius

A

1x10^-14 mol^2dm^-6

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

Why is [H2O] not included in the equation for Kw

A

Water is only weakly dissociated so equilibrium lies far over to the left and it’s concentration can be taken as constant

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

In pure water what must [H+]=

Therefore…?

A

[OH-]

Kw= [H+]^2

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

Is the dissociation of water exothermic?

A

No it is endothermic

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

Explain why pure water at 50 degrees celsius is not acidic despite being at a pH of 6.63

A

[H+]=[OH-]

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

Why does Kw increase with temperature

A

Equilibrium shifts to the right to decrease temperature
Degree of dissociation increases
Kw increases
pH increases

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

Define:

Monoprotic base

Diprotic base

A

Can accept 1 proton

Can accept 2 protons

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

Are hydroxides strong bases?

A

Yes

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

3 steps for calculating pH of diluted acid

A

1: calculate moles of H+
2: concert to concentration by dividing by new volume
3: pH=-log[H+]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Steps for working out pH of a strong base

A

1: calculate miles of OH-
2: convert to concentration by dividing by new volume
3: [H+]=Kw/[OH-]
4: pH=-log[H+]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
How do you calculate pH of a mixture of acid and base
* calculate moles of H+ * calculate moles of OH- * work out what is in XS and convert to concentration by dividing by total volume If H+ is in XS: pH=[H+] If OH- is in XS: [H+]=Kw/[OH-] pH=-log[H+]
26
Why must a pH meter be calibrated before use?
They do not give an accurate reading over time
27
How to calibrate a pH meter
Place meter in buffer solution of known pH and plot a calibration curve Eg rinse probe with deionised water, dry with a paper towel and place in buffer Wait for reading to steady then set meter to known pH of buffer
28
What is a buffer solution
Maintains same pH despite the addition of small amounts of acid, base, or water
29
Method for drawing a pH curve
Measure initial pH Add solution from burette in small portions Stir mixture Record pH after each addition Add solution dropwise as you near the end point After end point add solution 1cm3 at a time until in XS
30
What container do you use for a titration to find a pH curve
A beaker - NOT a conical flask | So both probe and burette can fit
31
What is the equivalence point
When sufficient base has been added to neutralise the acid (or vice versa)
32
Describe a pH curve of a: Strong Base added to a strong acid Strong base added to a weak acid
Very low to very high Low to very high
33
Describe the pH curve of a: Weak base added to a strong acid A weak base added to a weak acid
Very low to quite high Quite low to quite high
34
How to use pH curve to find concentration of acid or base
Use volume at end point (vertical line) to find concentration of substance added
35
What does pKa equal
pH
36
What is the half neutralisation point
Half way between the zero and equivalence point
37
What does Ka equal
[H+][A-] ————- [HA]
38
Why can Ka be simplified to Ka=[H+] at half neutralisation point
Half the acid has been neutralised so [HA]=[A-]
39
How to tell if it’s a half neutralisation point calculation
If one reactant has half the volume of the other but equal concentration Ie if one has half the moles of the other
40
What is an acid-base indicator
A water soluble, weak organic acid, whose acid form (HA) and base form (A-) have different colours
41
Why can only 2-3 drops of an acid-base indicator be added to a solution
It is acidic so it will affect pH otherwise
42
What happened when the indicator is placed in acidic solution
The extra H+ ions will push the equilibrium to the LHS so the colour of HA will be seen
43
What happened when the indicator is placed in alkaline solution
The extra OH- ions will react with the H+ ions, pushing the equilibrium to the RHS and so the colour of A- will be seen
44
What properties must a suitable indicator have
Colour change must be sharp rather than gradual at end point End point of the titration given by the indicator must be the same as the equivalence point Indicator should give a distinct colour change
45
When will change point for an indicator be
When [HA]=[A-] and neither colour dominates | At this point [H+]=Ka
46
pH at which the colour of the indicator changes =
pKa of the indicator
47
How do you calculate Ka from a titration pH curve?
From the curve, read off the volume at equivalence Divide this volume by 2 to find volume at half equivalence Read pH at the half equivalence volume - this will be your pKa value Calculate the 10^(-pKa) to find Ka
48
What is the molar ratio of a carbonate to a monoprotic acid?
1:2
49
Define buffer solution
A solution that resists change in pH when small amounts of acid, base or water are added
50
What can Ka be useful for?
To confirm an acid’s identity
51
The weaker the acid, the _____ it dissociates and the more the equilibrium lies to the ____ How about bases?
Less LHS Same for bases
52
Does water strongly dissociate? What does this mean for the equilibrium?
No- weakly dissociated Lies far to the left and conc of water is taken as constant
53
What is the ionic product of water
Kw Kc when water is taken as constant - [H+][OH-]
54
How does temperature affect Kw? Why?
Kw increases with temperature It involves breaking covalent bonds (inputting energy) and is an endothermic process
55
What are the two types of acidic buffer?
Weak acid and one of its salts Weak acid and strong acid (salt is made as a product of the reaction)
56
What is sodium ethanoate used for in an acidic buffer?
Acts as a source of conjugate base, CH3COO-
57
What is added to an alkaline buffer containing NH3
NH4+ Cl-
58
What happens in the equilibrium of blood when An Acid A Base Is added
a) extra H+ shift equilibrium to left to remove H+ | b) extra OH- remove H+ by reacting to form water. Equilibrium shifts left to replace H+
59
Give example of buffers in everyday life Why are buffers needed in them
Detergent Shampoo Wrong pH could damage fabric or skin and hair
60
For acidic what must you say after explains buffer action?
The ratio of [HA] ———— [A-] Remains constant
61
How many moles of Fe2+ react with one chromate ion?
6
62
Is there any point rearranging equations before putting in numbers?
Yes - you get a mark for it
63
Why is the gradient of a PH curve initially near 0?
Buffer formed (excess weak acid and strong base)
64
Describe pH curve of strong base to weak acid
Initial ‘ramp up’ | Near horizontal until endpoint where curve is vertical and then levels out
65
What must you dip the probe in to calibrate it?
Buffer solutions (pH 4, pH 7 and pH10)
66
Can you swirl when doing investigate pH
No - mixture in a beaker so must stir
67
How to work out original [HX] from incomplete pH curve
At equivalence point n OH- = n HX So divide volume added at equivalence point by original volume of HX

A Level Chemistry (11 decks)

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