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Chemistry > Chapter 20 > Flashcards

Chapter 20 Flashcards

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1
Q

What is an acid?

A

It is when a aqueous solution dissociates releasing H+ ions

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2
Q

What is an alkali?

A

A soluble base which releases OH- ions when it dissociates

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3
Q

What is a neutralisation reaction?

A

acid + base –> salt (H+ is replaced with a metal ion or NH4+)

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4
Q

What is a Bronsted Lowry acid?

A

A proton donor

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5
Q

What is a Bronsted Lowry base?

A

A proton acceptor

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6
Q

What does an acid base reaction involve?

A

A proton transfer

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7
Q

What is a strong acid?

A

When it fully dissociate in water releasing H+ ions eg HCl

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8
Q

What are the conjugate acid base pairs in HCl.

A

HCl and Cl- are the conjugate base pairs

  • In the forward direction Cl- is the conjugate base as HCl releases a proton
  • In the reverse direction HCl is the conjugate acid as the Cl- accepts a proton
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9
Q

What is a weak acid?

A

An incomplete dissociation of H+ ions this is shown by an equilibrium. e.g CH3COOH

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10
Q

What are the conjugate base pairs in ethanoic acid?

A
  • CH3COO- is the conjugate base of CH3COOH

- CH3COOH is the conjugate acid of CH3COO-

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11
Q

What happens when an acid releases a proton?

A

It forms a conjugate base

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12
Q

What happens when a base accepts a proton?

A

It forms a conjugate acid

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13
Q

What is a conjugate acid base pair?

A

It’s when two species can be interconverted by a proton transfer.

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14
Q

What are monobasic, dibasic, tribasic acids?

A

Acids which refer to the number of H+ in the acid which can be replaced per mole in an acid base reaction. The number of hydrogen is in the formula give a clue to the type of acid.

e.g HCl - monobasic CH3COOH - monobasic
H3BO3 - tribasic

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15
Q

What is the simplified formula for neutralisation?

A

H+ + OH- –> H2O

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16
Q

Describe the dissociation using a hydronium ion?

A

In aqueous solution dissociation requires a proton transfer from an acid to a base which won’t happen unless water is present. Water acts as a base as accept a proton. The hydronium ion is the conjugate acid as H2O excepted a H plus ions (it’s an active acid ingredient in any aqueous acid).

H3O+ + OH- –> 2H2O

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17
Q

What are Spectator ions?

A

Ions don’t change in the reaction these can be cancelled out when writing an ionic equation.

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18
Q

Show the equation for neutralisation of acid with carbonates?

A

acid + carbonate –> salt + carbon dioxide + water

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19
Q

Show the equation for neutralisation of acid with metal oxides/hydroxide?

A

acid + metal oxide/hydroxide –> salt + water

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20
Q

Show the equation for neutralisation of acids with alkalis ?

A

acid + alkali –> salt + water

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21
Q

Show the equation for neutralisation of acids with metals?

A

acid + metal –> salt + hydrogen

Undergo a redox reaction

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22
Q

How can an acid be written in a equation

A

2H+

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23
Q

What does pH> 7 show?

A

Increasing alkalinity

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24
Q

What does pH< 7 show?

A

Increasing acidity

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25
Q

What does pH = 7 show?

A

Neutral

26
Q

What does a low [H+] match with?

A

A high pH

27
Q

What does a high [H+] match with?

A

A low pH

28
Q

What is the equation for pH and [H+]?

A 
pH = -log[H+]
[H+] = 10^ -pH
29
Q

How many times concentrated is pH 1 to pH 2

A

x 10

30
Q

If you had to dilute a solution from pH1 to pH4 what would it require?

A

A dilution of 1000 times

31
Q

How many times more does pH1 have of H+ compared to pH 14?

A

10^13

32
Q

What is the general formula for a strong acid?

A

HA –> H+ + A-

33
Q

Describe the relationship between [H+] and [HA] in a strong acid?

A

[H+] = [HA]

34
Q

What is the acid dissociation constant Ka?

A

The extent of dissociation is different for different weak acids, so the position of equilibrium differs. The further to the right the stronger the weak acid.

35
Q

What is the equation for Ka?

A

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

36
Q

What is Ka standardised at?

A

25 degrees and is temperature dependent

37
Q

How do you work out Ka?

A

10^ -pKa

38
Q

How do you work out pKa?

A

pKa = -logKa (should be given to 2dp)

39
Q

What happens to the value of Ka and pKa when the acid is stronger?

A

LARGER the Ka value

SMALLER the pKa value

40
Q

What happens to the value of Ka and pKa when the acid is weaker?

A

SMALLER the Ka value

LARGER the pKa value

41
Q

Describe the relationship between [H+] and [HA] in a weak acid?

A

[H+] not equal [HA]

42
Q

What does [H+] depend on?

A

Conc of acid [HA]

Ka

43
Q

What happens when HA molecules dissolve?

A

[H+] and [A-] form equal quanities

44
Q

What is approximation 1 ?

A

[HA] dissociates to produce [H+] = [A-]
There will be a small conc of H+ from water dissociation but it can be neglected.
[H+] = [A-]

45
Q

What is approximation 2?

A

[HA] eqm = [HA]start - [H+]eqm
As the dissociation of weak acids is small you can assume [HA] > [H+] and you can neglect any decrease in HA concentration from the dissociation.
[HA] eqm = [HA] inital

46
Q

From approximation 2 how to work out Ka?

A

Ka = [H+]^2 / [HA]

47
Q

From approximation 2 how to work out [H+]?

A

square root Ka x [HA]

48
Q

Accuracy on approximation 1?

A

[H+] = [HA]. At 25 degrees water is pH 7, so [H+]= 1 x 10^-7. If weak acid> ph6 i.e [H+] of less than 1 x 10^-6 the contribution of [H+] from water dissociation will be significant, so breaks down very weak or dilute acids

49
Q

Accuracy on approximation 2?

A

[HA] eqm = [H+] inital

The approximation breaks down for stronger weaker acids (Ka > 1 x 10 ^-2 )

50
Q

How can Ka be determined?

A

Preparing a standard solution of the week acid of known concentration.
Measuring pH with a pH meter of a standard solution.

51
Q

As water ionises very slightly what does it act as?

A

Both an acid and a base setting up the acid base equilibrium.
H2O + H2O –> H3O- + OH-

52
Q

As water dissociation is very small what can the concentrations be regarded as?

A

As the concentration is basically remain and changed they can be regarded as a constant.
Ka (constant ) x [H2O] (constant ) = [H+][OH-]

53
Q

What is Kw?

A

The ionic product of water. It is essentially an equilibrium constant which controls [H+] and
[OH-] concentrations. This value varies with temperature at 298K (25 degrees) = 1.00 x 10^-14 mol2dm-6
Kw = [H+][OH-]

It sets up the neutral point of the pH scale

54
Q

When is the solution neutral?

A

[H+] = [OH-]

55
Q

When is a solution acidic?

A

[H+] > [OH-]

56
Q

When is a solution alkaline?

A

[H+] < [OH-]

57
Q

What will acidic solution still contain?

A

It will still contain OH- ions but just a small proportion compared to H+ ions.

58
Q

What is a strong base?

A

An alkali which completely dissociate in solution releasing OH- ions e.g group 1 and group 2 hydroxides.

59
Q

How is the pH of a strong base calculated?

A

The concentration of the base and the ionic product of water Kw

60
Q

Four whole number PH is what must the [H+]

[OH-]concentrations add up to?

A

-14

61
Q

What are weak bases?

A

They are also alkali. Ammonia gas partially dissolves in water releasing OH ions. An equilibrium is set up with a position to the left. One mole of NH3 releases far less than 1 mole of OH- ions.

Chemistry (23 decks)

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