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Chemistry > CH21 Acids and Bases > Flashcards

CH21 Acids and Bases Flashcards

1
Q

Define a Bronsted-Lowry acid

A

Proton donor

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2
Q

Define a Bronsted-Lowry base

A

Proton acceptor

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3
Q

What ion causes a solution to be acidic

A

H+ ion or H3O+ (oxonium) ion, as protons react with water to form oxonium

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4
Q

What ion causes a solution to be alkaline

A

-OH ion

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5
Q

Ionisation of water

A

2H2O ⇌ H3O+ + -OH

H2O ⇌ H+ + -OH

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6
Q

Kw equation

A

Kw = [H+][OH-]

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7
Q

Value of Kw at 298K

A

1.0 x 10˄-14

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8
Q

Physical factor which affects Kw

A

Temperature - equilibrium shifts right if there is an increase in temperature so Kw increases and pH of pure water decreases

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9
Q

Why is pure water still neutral, even if pH does not equal 7

A

[H+] = [OH-]

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10
Q

Expression for pH in terms of H+

A

pH = -log10 [H+]

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11
Q

Relationship between pH and concentration of H+

A

Lower pH = higher concentration of H+

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12
Q

If 2 solutions have a pH difference of 1, what is their difference in [H+]

A

A factor of 10

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13
Q

How do you find [H+] from pH

A

[H+] = 10˄-pH

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14
Q

How do you find [OH-] from pH at 298K

A

Find [H+]
Use Kw - 1x10˄-14
Calculate [OH-}

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15
Q

Difference between finding [H+] from the concentration of diprotic and triprotic acids

A

need to multiply the concentration of acid by the number of protons to find [H+]

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16
Q

How do you calculate the pH of a strong alkaline solution

A

Use Kw to calculate [H+] from [OH-]

Use pH = -log[H+]

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17
Q

Define term strong acid

A

One which fully dissociates in water

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18
Q

Define the term strong base

A

One which fully dissociates in warer

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19
Q

Difference between concentrated and strong

A

Concentrated means may mol per dm3

Strong refers to amount of dissociation

20
Q

What is a weak acid and weak base

A

Do not fully dissociate in water.

Only partially dissociate into their ions

21
Q

Examples of strong acids

A

HCl
H2SO4
H3PO4

22
Q

Examples of strong bases

A

NaOH
CaCO3
Na2CO3

23
Q

Examples of weak acids

A

CH3COOH

24
Q

Examples of weak bases

A

NH3

25
Q

Expression for Ka (strong acid)

A

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

26
Q

How to work out pH of a weak acid

A

Use Ka - substitute values [A-] and [HA]

Use pH = -log[H+]

27
Q

What is a titration

A

The addition of an acid/base of known titration to a base/acid of unknown titration to determine its concentration

28
Q

Define equivalence point

A

The point at which the exact volume of base has been added to just neutralise the acid

29
Q

What generally happens to pH of solution around equivalence point

A

Large and rapid change in pH, except in weak-weak titration

30
Q

How to calculate conc of a reactant if volume of it and volume and conc of other reactant are known

A

Calc mol of one reactant
USe balanced equation
USe cone = mol/vol to calculate conc

31
Q

What is the end point

A

The volume of acid or alkali added when the indicator just changes colour. If right indicator is chosen - equivalence point = end point

32
Q

Properties of a good indicator

A

Sharp colour change
End point same as equivalence point
Distinct colour change

33
Q

Indicator used for strong acid - strong base titration

A

Phenopthalein or methyl orange

34
Q

Indicator used for strong acid-weak base titration

A

Methyl orange

35
Q

Indicator used for weak acid - strong base titration

A

Phenolpthalein

36
Q

Indicator used for weak acid - weak base titration

A

Neither methyl orange or phenolpthalein as neither give sharp change at end point

37
Q

Colour of methyl orange in acid and alkali. What pH does it change at

A

Acid: Red
Alkali: Yellow
Changes at 4-5 pH

38
Q

Colour of phenolpthalein in acid and alkali. What pH does it change at

A

Acid: Colourless
Alkali: Red
Changes at 9-10 pH

39
Q

What is the half-neutralisation point

A

When volume = half the volume that has been added at the equivalence point

40
Q

Define a buffer solution

A

A solution that can resist changes in pH when small amount of acid / alkali are added

41
Q

What do acidic buffer solution contain

A

A weak acid and a soluble salt of that acid that fully dissociates

42
Q

Reaction of acidic buffer with added acid

A

A- + H+ –> HA

opposes addition of H+

43
Q

Reaction for acidic buffer with added alkali

A

HA + OH- –> H20 + A-

44
Q

How else can an acidic buffer solution be made

A

Neutralise half of a weak acid with an alkali

Forms a weak acid / soluble salt mixture

45
Q

What do basic buffer solutions contain

A

Weak base and a soluble salt of that weak base

46
Q

How to calculate pH of buffer solutions

A

Use Ka of weak acid
Calculate [H+]
Calculate pH

47
Q

How to calculate new pH of buffer solution when acid or base is added

A

Calc number of mol of H+ and A - and HA before addition of acid or base
Work out new mol of A- and HA
Find [H+]
Calculate pH

Chemistry (18 decks)

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