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adv higher chemistry > unit 1b: pH > Flashcards

unit 1b: pH Flashcards

1
Q

water dissociation

A

in water and aqueous solution, there is an equilibrium between the water molecules and hydronium and hydroxide ions

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2
Q

hydronium ion

A

H3O^+ (H^+ (aq) shorthand)

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3
Q

brønsted-lowry definition of acids and bases

A

an acid is a proton donor, a base is a proton acceptor

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4
Q

when an acid donates a proton, the species left behind is the

A

conjugate base of the acid

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5
Q

when a base accepts a proton, the species formed is called the

A

conjugate acid of the base

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6
Q

amphoteric

A

it can react as both an acid and a base (water is amphoteric)

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7
Q

the dissociation constant

A

Kw, known as the ionic product of water

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8
Q

ionic product of water

A

[H3O^+] [OH^-]

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9
Q

Kw varies with

A

temperature

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10
Q

at 25°C, the value of Kw is

A

approximately 1x10^-14

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11
Q

in water and aqueous solutions with a pH value of 7, the concentrations of hydronium and hydroxide ions are

A

10^-7 moll^-1 at 25°C

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12
Q

strong acids and bases

A

those that completely dissociate (ionise) when dissolved in water

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13
Q

examples of strong acids

A

sulphuric acid, nitric acid, hydrochloric acid

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14
Q

examples of strong bases

A

sodium hydroxide, potassium hydroxide

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15
Q

weak acids and bases

A

only partially dissociate in water, an equilibrium (which lies to the left) is set up

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16
Q

examples of weak acids

A

carboxylic acids

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17
Q

examples of weak bases

A

ammonia, amines

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18
Q

equimolar solutions

A

same concentration

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19
Q

compared to a weak acid, a strong acid has

A

lower pH, higher conductivity, faster rate of reaction

20
Q

compared to a weak base, a strong base has

A

higher pH, higher conductivity, faster rate of reaction

21
Q

acid dissociation constant

22
Q

pKa values are used when

A

calculating the pH of a weak acid to take into account the degree of dissociation

23
Q

the larger the pKa

A

the weaker the acid

24
Q

a salt of a strong acid and a weak base will form

A

an acidic solution

25
Q

a salt of a weak acid and a strong base will form

A

a basic solution

26
Q

a salt of a strong acid and a strong base will form

A

a neutral solution

27
Q

when in solution, all salts…

A

completely ionise

28
Q

a buffer solution

A

one in which the pH remains approximately constant when small amounts of acid, base, or water are added

29
Q

use of buffers

A

stabilise pH by being able to absorb extra acid or alkali

30
Q

acid buffer

A

a solution of a weak acid and a salt of the weak acid

31
Q

basic buffer

A

a solution of a weak base and a salt of the weak base

32
Q

acid buffer solution use

A

when a base is added it removes H+ ions, the weak acid can supply hydrogen ions. when an acid is added it adds H+ ions, the salt provides the conjugate base which removes extra H+ ions

33
Q

basic buffer solution use

A

when an acid is added it adds H+ ions, the weak base removes hydrogen ions. when a base is added it removed H+ ions, the salt provides the conjugate acid which supplies H+ ions

34
Q

adding water to a buffer

A

does not affect the pH as [acid]/[salt] is a ratio

35
Q

indicators

A

are weak acids which change colour depending on pH

36
Q

acid indicator dissociation constant

37
Q

the colour of an acid indicator

A

is distinctly different to the colour of its conjugate base

38
Q

colour change in an indicator can only be distinguished when

A

HIn and In- differ by a factor of 10

39
Q

acid indicator shorthand

40
Q

conjugate base indicator shorthand

41
Q

equivalence point for strong acid/ strong base

A

pH7, an indicator which changes colour around pH7 is suitable

42
Q

equivalence point for a strong acid/ weak base

A

around pH5, an indicator which changes colour at an acid pH is suitabel

43
Q

equivalence point for a weak acid/ strong base

A

around pH9, an indicator which changes colour at a basic pH is suitable

44
Q

suitable indicator for weak acid/ weak base

A

not possible as the pH does not change rapidly enough, the curve does not have a vertical section like the others

45
Q

equivalence point

A

the mid point of the rapid increase in pH

46
Q

concentration=

47
Q

why does adding H+ to the salt of the weak acid result in the formation of undissociated weak acid molecules

A

H+ ions react with the conjugate base

adv higher chemistry (18 decks)

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