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Chemistry > 20) Acids, bases and pH > Flashcards

20) Acids, bases and pH Flashcards

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1
Q

Define BrØnsted-Lowry acid

A

a species that is a proton donor

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2
Q

Define BrØnsted-Lowry base

A

a species that is a proton acceptor

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3
Q

Define conjugate acid-base pair

A

two species that can be interconverted by the transfer of a proton

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4
Q

Define conjugate acid

A

a species that releases a proton to form a conjugate base

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5
Q

Define conjugate base

A

a species that accepts a proton to form a conjugate acid

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6
Q

How can acid-base pair by clearly linked together?

A

labelling acid 1 base 1, acid 2 base 2

arrow links

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7
Q

Dissociation does not take place unless…?

A

water is present

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8
Q

Define hydronium ion

A

H3O+ (aq); active ingredient in any aqueous acid and conjugate acid for water

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9
Q

What is the simplified form of a hydronium ion?

A

H+

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10
Q

What do the terms monobasic, dibasic and tribasic refer to?

A

the total number of hydrogen ions in the acid that can be replaced per molecule in an acid-base reaction

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11
Q

Define spectator ions

A

ions that do not change during a reaction and therefore, can be cancelled out from ionic equations

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12
Q

What do ionic equations help to do?

A

emphasise the role of H+

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13
Q

How should you write a solid in an ionic equation?

A

with the full formula

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14
Q

What is the ionic equation for neutralisation of acids with alkalis?

A

H+(aq) + OH-(aq) -> H2O(l)

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15
Q

For any solution at 25 degrees C, pH < 7 indicates?

A

decreasing acidity

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16
Q

For any solution at 25 degrees C, pH = 7 indicates?

A

neutral

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17
Q

For any solution at 25 degrees C, pH > 7 indicates?

A

increasing alkalinity

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18
Q

How can pH be measured?

A

indication paper

pH meter

19
Q

pH = ?

A

-log [H+(aq)]

20
Q

[H+(aq)] = ?

A

10^-pH

21
Q

A low value of [H+] matches a _ value of pH and vice versa.

A

high

22
Q

pH is a _ scale, this means that a pH of 1 has _ times the [H+] as a solution with a pH of 2?

A

logarithmic

10

23
Q

Give the equation for the pH of strong acids

A

[H+(aq)] = [HA(aq)]

because a strong acid completely dissociates its H+

24
Q

Define acid dissociation constant Ka

A

equilibrium constant that shows the extent of dissociation of a weak acid

25
Q

Ka = ?

A

( [H+(aq)] [A-aq)] ) / [HA(aq)]

26
Q

Does temperature change Ka?

A

yes

27
Q

The larger the numerical value of Ka, the further the equilibrium is to _ and the _ dissociation and acid strength?

A

right

greater

28
Q

pKa = ?

A

-log Ka

29
Q

Ka from pKa?

A

Ka = 10^-pKa

30
Q

The stronger the acid, the _ the Ka val. and the _ the pKa value?

A

larger

smaller

31
Q

Give the 2 key equations for the pH of weak acids

A
  1. ka = [H+(aq)]^2 / [HA(aq)]

2. [H+(aq)] = √(Ka x [Ha])

32
Q

What 2 approximations is the key equation for the pH of weak acids based upon?

A
  1. [H+(aq)]eqm = [A-(aq)]eqm
    the small amount of H+ from the dissociation of water is neglected
  2. [HA(aq)]start = [HA(aq)]eqm
    dissociation of weak acids is small so any decrease in [HA] from dissociation is neglected
33
Q

Give the simplified equation for the pH of weak acids

A

Ka = ( [H+(aq)]eqm x [H+(aq)]eqm ) / ( [HA(aq)]start - [HA(aq)]eqm )

34
Q

How can Ka be determined experimentally?

A

preparing a standard solution of the weak acid of known conc. and measuring the pH of the standard solution using a pH meter

35
Q

When does the approximation that [H+(aq)]eqm = [A-(aq)]eqm for weak acids break down?

A

for very weak acids or very dilute solutions as if pH > 6 the dissociation of water becomes significant

36
Q

When does the approximation that [HA(aq)]start = [HA(aq)]eqm for weak acids break down?

A

for stronger weak acids w/ Ka > 10^-2 moldm^-3 or very dilute solutions as [H+] becomes significant and there is a real difference between [HA(aq)]eqm and [HA(aq)]start - [HA(aq)]eqm

37
Q

Define ionic product for water Kw

A

the product of the ions formed by partial dissociation of water, given by Kw = [H+(aq)] [OH-(aq)]

38
Q

At 25 degrees C, Kw = _ therefore, neutral water has a pH of _ as [H+] = _?

A

1.00 x 10^-14 mol2dm-6
7
[OH-(aq)]

39
Q

If [H+] > [OH-] in a solution it is _?

A

acidic

40
Q

If [H+] < [OH-] in a solution it is _?

A

alkaline

41
Q

Define strong base

A

an alkali that completely dissociates in solution e.g. NaOH

42
Q

Can bases be monobasic, dibasic and tribasic?

A

yes

43
Q

Give the key equation for the pH of solutions of strong bases

A

[H+(aq)] = Kw / [OH-(aq)]

uses concentration of the base and the ionic product of water

44
Q

HSO3- can act as either a BrØnsted-Lowry acid or a BrØnsted-Lowry base. Explain this statement, including equations for the reactions of HSO3-(aq) with H+(aq) and OH-(aq)

A

can accept protons acting as a base
HSO3-(aq) + H+(aq) -> H2SO3
can donate protons acting as an acid
HSO3-(aq) + OH-(aq) -> SO3 + H2O (neutralisation)

Chemistry (31 decks)

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