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Chemistry U6 > Acids and bases > Flashcards

Acids and bases Flashcards

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1
Q

What is a Brønsted Lowry Acid

A

Proton donor

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2
Q

Why is H2SO4 a stronger acid compared to HA?

A

it can donate more protons

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3
Q

What is a Brønsted Lowry base

A

proton acceptor

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4
Q

What is a strong acid

A

completely dissociates into ions in aq solution

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5
Q

What is a monoprotic acid

A

donates 1 H+ per molecule

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6
Q

What is a Diprotic acid?

A

Donates 2 H+ ions per molecule

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7
Q

What is a Strong base?

A

*completely dissociates** into ions in aq solution

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8
Q

What is a weak acid?

A

partially dissociates into ions in aq solution

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9
Q

What is a weak base?

A

slightly dissociates to give ions in aq solution

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10
Q

What is the equation for pH?

A

-log10[H+]

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11
Q

As the concentration of H+ ions increase what happens to the pH?

A

decrease

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12
Q

How can you calculate H+ from pH

A

H+ = 10^-pH

(divide by no. H)

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13
Q

What is the equation for water

A

H20 ⇌ H+ + OH-

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14
Q

Why is the concentration of water very high?

A

water is weakly dissociated so equilibrium lies far to the left

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15
Q

What is the equation for Kw?

A

Kw = [H+] [OH-]

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16
Q

What is the equation for Kw in pure water

A

Kw = [H+]^2

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17
Q

What is a monoprotic base?

A

base that can accept one proton

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18
Q

What is a diprotic base?

A

Base that can accent two protons

(has 2 OH’s e.g Ba(OH)2)

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19
Q

How can you calculate the pH of a Strong base?

A

use concentration of the base to find [OH-]

use Kw to find [H+]

convert [H+] into pH

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20
Q

how can you calculate the concentration og [OH-] from pH

A

use pH to find [H+]

use Kw to find [OH-]

use [OH-] to find conc of base

divide by no. of OH

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21
Q

How can you calculate the pH of a strong acid after it has been diluted with water?

A

calculate moles of [H+]

work out new volume

convert to concentration by dividing by volume

calculate pH

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22
Q

How can you calculate the pH of a strong base after dilution?

A

calculate moles of [OH-]

calculate the new volume

convert to concentration

[H+] = Kw / [OH-]

calculate pH

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23
Q

What is the value of Kw at room temperature?

A

1 x 10^-14

24
Q

How can you calculate the pH of a mixture of acid and alkali?

A
  • calculate moles of H+
  • Calculate moles of OH-
  • Work out which one is in excess (largest number) and calculate the remaining moles
  • convert two concentration by by the total volume
25
Q

Why are strong acids not in equilibrium?

A

They fully ionise in water

26
Q

why is the Kc of weak acids/bases small?

A

weak acids/bases partially ionise in water and the equilibrium lies to the left

27
Q

What is the equilibrium of weak acids?

A

HA ⇌ H+ + A-

28
Q

what is the equation for the acid dissociation constant Ka?

A

Ka = [H+] [A-]
————-
[HA]

29
Q

what are the units of Ka?

A

mol dm-3

30
Q

what is the equation for dissociation of an acid?

A

eg ethanoic acid

CH3COOH ⇌ H+ + CH3COO-

31
Q

which acids have a Ka less than one?

A

Weak acids

32
Q

Which assets have a KA more than one?

A

Strong acids

33
Q

what is the formula for pKa

A

pKa = -logKa

34
Q

how can you determine Ka from a pKa value

A

Ka = 10^-pKa

35
Q

what are the two assumptions for an aqueous solution a weak acids?

A
  • The dissociation of HA is very small so the [HA] remains effectively constant
  • [HA] at equilibrium = [HA] initial (1:1)
36
Q

What is the simplest equation for dissociation of weak acids?

A

Ka = [H+]^2
-———
[HA]

37
Q

what happens in an acid base titration?

A

Base is added from a burette to a measured amount of an acid with a known concentration until an indicator shows that it has been neutralised

38
Q

what is a PH meter?

A

Digital device that can determine the pH of a solution by a place saying the pro in it

It can track pH during a titration

Must be calibrated before use

39
Q

Why must PH metres be calibrated?

A

Because BH means to do not give accurate readings overtime

40
Q

how do you calibrate a pH meter

A

Place probe and buffer solution of known pH and plot calibration curve

  • Rinse probe with deionised water and dry
  • Place in pH 4 buffer
  • Take out rinse and place in pH 7 and 10
  • Plot a graph pH buffer against measured pH
41
Q

how do you do an acid based titration with a ph probe

A
  • Measure the pH of unknown volume of acid
  • Add base from the burettr in small portions
  • Stir
  • Record pH after each addition
  • Add base drop by drop at a near the end point
  • after the end point add base slowly until it is in excess
42
Q

how does the pH change in an acid base titration?

A

As the basis added the pH gradually increases

43
Q

When does the pH highly increase in a titration?

A

when one drop of the base changes the mixture from being acid in access to being base in excess

there is a rising pH until it levels off

44
Q

what is the equivalence point?

A

When the moles of alkali added equals a mole of acid present (1:1)

rapid change in pH

45
Q

What is the endpoint of a titration?

A

when the indicator changes colour
The end point should concede with the equivalence point

46
Q

What is the pH range for an indicator for a titration with a strong acid and strong base

A

3-10

47
Q

What is the pH range for an indicator in a titration with a weak acid and strong base

A

8-10

48
Q

What is the pH range for an indicator for a titration with a strong acid and weak base

A

3-6

49
Q

What is the pH range for an indicator in a titration with a weak acid and a weak base?

A

There is no suitable indicator because there is no sharp end point

50
Q

how do you use a pH code to find the concentration of an acid?

A
  • Work out the moles of base
  • 1:1 ratios of acid are the same
  • Workout concentration (moles/olume)
51
Q

what is the half equivalence point?

A

put halfway along the axis between the zero and equivalence point

pH = pKa

52
Q

how do you calculate Ka from a titration pH curve?

A
  • divide the volume equivalence by 2 to find the volume at half equivalence
  • read the pH at half equivalence this will be pKa

-10^-pKa to find Ka

53
Q

What is an indicator?

A

A weak acid whose acid form (HIn-) and base form (In/)have different colours

54
Q

what colour is phenophthalein?

A

acid - colourless

base - pink

55
Q

What colour is methyl orange?

A

acid - red

base - yellow

56
Q

what properties must a suitable indicator for a titration need?

A
  • colour change must be sharp rather than gradual at the end point
  • end point given by the indicator must be the same as the equivalence point otherwise titration will give us the wrong answer
  • Indicator should give a distinct colour change

Chemistry U6 (6 decks)

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