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HDSO Chemistry REDOX A > acids and bases part 2 > Flashcards

acids and bases part 2 Flashcards

1
Q

what is added in an acid-base titration

A

a solution of a base of known concentration from a burette, to a measured amount of acid

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2
Q

what is used to find the end point in acid-titration

A

an indicator

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3
Q

how can the concentration of the acid be calculated in an acid base titration

A

from the volume of base required

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4
Q

what is a titration curve

A

a plot of pH against volume of base added

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5
Q

how is the pH measured

A

pH meter

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6
Q

what does the shape of a titration curve depend on

A

the strength of the acid and base used

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7
Q

key features of titration curve: strong acid and strong base

A
  • low starting pH
  • long vertical sector
  • high end pH
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8
Q

key features of titration curve: strong acid weak base

A
  • low starting pH
  • shorter vertical sector
  • lower end pH
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9
Q

key features of titration curve: weak acid and strong base

A
  • higher starting pH
  • shorter vertical sector
  • high end pH
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10
Q

pH at equivalence point: strong acid and strong base

A

7

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11
Q

pH at equivalence point: strong acid weak base

A

5

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12
Q

pH at equivalence point: weak acid strong base

A

9.5

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13
Q

equivalence point

A

the point at which the acid and base are in the correct molar ratio

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14
Q

an indicator for an acid base titration

A

weak acid (HIn)

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15
Q

why do different indicators change colour at different pH values

A

they have different Ka values

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16
Q

when is the end point of a titration

A

the point at which the indicator changes colour

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17
Q

for a successful titration, which two points must correspond

A

equivalence and end point- so that indicator changes sharply at equivalence point

18
Q

what must the pH range of the chosen indicator correspond to

A

the region of rapid pH change (vertical portion of pH curve)

19
Q

buffer

A

a solution that maintains an approximately constant pH on addition of small amounts of acid/base

20
Q

applications of buffers

A

shampoos and biological washing powder

21
Q

what is an acidic buffer a mixture of

A

a weak acid and one of its salts

22
Q

what does an acidic buffer maintain a pH of

A

below 7

23
Q

in what two ways can an acidic buffer be made

A

add together HA and its salt, A-

partly neutralise HA with NaOH

24
Q

buffer action (HA>

A

A- reacts with added H+ to create HA

equilibrium shifts to left hand side

25
Q

buffer action (HA>

A

OH- reacts with H+ to create H2O- equilibrium shifts to RHS

26
Q

what concentrations are much greater in buffer solutions

A

[HA] and [A-] much greater than [H+]

27
Q

what does the pH of a buffer solution depend on

A

the Ka of the acid and the [HA]:[A-]

28
Q

how to work out [H+] in a buffer solution

A

Ka[HA]/[A-]

29
Q

why doesn’t volume need to be taken into account in buffer solution calculations

A

cancel eachother out

30
Q

the buffer range

A

the range of pH values which a buffer solution using a particular weak acid can have

31
Q

what is the buffer range usually for a weak acid

A

pKa +/- 1

32
Q

Required practical: pipette 25.0 cm3 of the…

A

Acid into a tall form beaker and add a few drops of the appropriate indicator

33
Q

Required practical: place the tall form beaker on top of a

A

Magnetic stirrer and place the magnet in the beaker

34
Q

Required practical: fill the bursts with

A

The base

35
Q

Required practical: rinse the electrode with distilled water and dip it into the acid in the

A

Beaker

36
Q

Required practical: record the pH in a

A

Results table

37
Q

Required practical: results table should include

A

pH of solution and colour of indicator

38
Q

Required practical: switch on the stirrer and make sure

A

That the magnet doesn’t strike the electrode when in position

39
Q

Add 5cm of the

A

Base from the burette and note both the pH and the indicator colour

40
Q

Required practical: continue adding the base, taking readings every

A

5cm3 intervals for first 20cm3

Then every 1cm3 until 23.0cm3

Around equivalence you should add base in 0.5cm3 portions

Return to 1cm3 portions until 30.0cm3

Then 5cm3 portions until 50.0cm3 base added

41
Q

Required practical: plot a graph of pH against

A

Volume of base added

HDSO Chemistry REDOX A (5 decks)

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