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Chemistry Alevel OCR YR 13 > Acids and bases > Flashcards

Acids and bases Flashcards

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1
Q

Bronsted- Lowry acids are?

A

proton donors

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2
Q

Bronsted-Lowry bases are?

A

proton acceptors

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3
Q

Describe how acids are proton donors

A

dissociation is required for a proton to be transferred from an acid to a base- this requires water. Water behaves as a base and accepts a proton forming H3O+(aq)

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4
Q

Describe H3O+(aq)

A

-conjugate acid
-active acid ingredient, ions make solution acidic
-simple version is H+

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5
Q

Bronsted-Lowry bases are?

A

proton acceptors

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6
Q

Describe strong and weak bases?

A

-strong bases dissociate (ionise) almost completely
-weak bases dissociate poorly

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7
Q

Describe strong and weak acids?

A

-strong acids dissociate (ionise) almost completely
-weak acids dissociate poorly

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7
Q

Describe strong and weak acids?

A

-strong acids dissociate (ionise) almost completely
-weak acids dissociate poorly

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8
Q

Describe weak acids and provide examples?

A

-backwards reaction favoured so not many H+ produced
-e.g carboxylic acids

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9
Q

Describe strong acids and provide examples?

A

-forwards reaction favoured strongly. Lots of H+ produced.
-e.g HCl, H2SO4, HNO3

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10
Q

Describe strong bases and provide examples?

A

-forward reaction favoured strongly. Lots of OH- ions produced.
-e.g NaOH and KOH

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11
Q

Describe weak bases and provide examples?

A

-backwards reaction favoured so not many OH- ions produced
-e.g NH3

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12
Q

Acid dissociation equation?

A

HA(aq) (acid) + H2O(l) (reversible arrow) H3O+(aq) + A-(aq)

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13
Q

Base dissociation equation?

A

B(aq) (base) + H2O(l) (reversible arrow) BH+(aq) + OH-(aq)

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14
Q

Water dissociation equation?

A

2 H2O (reversible arrow) H3O+ + OH-
simpler version: H2O (reversible arrow) H+ + OH-

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15
Q

Describe the dissociation of water?

A

water dissociates into its ions very weakly. There is so little OH- and H+ ions compared to H2O molecules that we assume the concentration of water has a constant value

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16
Q

what are polyprotic/ polybasic acids?

A

acids which can donate more than one proton

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17
Q

Describe monoprotic/ monobasic acids? provide example

A

e.g HNO3
1 mole of HNO3 will produce 1 mole of H+ ions

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18
Q

Describe diprotic/ dibasic acids? provide example

A

e.g H2SO4
1 mole of H2SO4 will produce 2 moles of H+ ions

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19
Q

Describe triprotic/ tribasic acids? provide example

A

e.g H3PO4
1 mole of H3PO4 will produce 3 moles of H+ ions

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20
Q

Describe how ammonia acts as a base?

A

-Ammonia doesn’t produce OH- ions directly. It reacts with water first and accepts a proton to produce ammonium ions (NH4+) and OH- ions
-ammonia reacts with acids to make ammonium salts but no water

21
Q

Equation showing ammonia acting as a base?

A

NH3(aq) + H2O(l) (reversible arrow) NH4+(aq) +OH-(aq)

22
Q

Acid + alkali ->

A

salt + water

23
Q

Metal + Acid ->

A

salt + hydrogen

24
Q

metal oxide + acid ->

A

salt + water

25
Q

metal hydroxide + acid ->

A

salt + water

26
Q

metal carbonate + acid ->

A

salt + carbon dioxide + water

27
Q

what are the rules when writing an ionic equation?

A

1) write balanced equation
2)add state symbols
3)separate aqueous into ions
4)cancel out spectator ions

28
Q

can state are metal oxide in?

A

solid

29
Q

How are conjugate pairs linked?

A

they are linked by transferring of a proton

30
Q

what is a conjugate acid?

A

a species that has gained a proton

31
Q

what is a conjugate base?

A

a species that has lost a proton

32
Q

equation for reaction between Bronsted-Lowry acids and bases? and describe

A

HA (acid) + B (reversible arrow) BH+(acid) + A-(base)
- HA is an acid in the forward reaction as it donates a proton
- A- is a base in the reverse direction as it accepts a proton from BH+ to form HA

33
Q

What are the conjugate pairs in the equilibrium reaction between Bronsted-Lowry acids and bases?

A

conjugate pair: HA (conjugate acid) and A- (conjugate base)
conjugate pair: BH+ (conjugate acid) and B (conjugate base)

33
Q

What are the conjugate pairs in the equilibrium reaction between Bronsted-Lowry acids and bases?

A

conjugate pair: HA (conjugate acid) and A- (conjugate base)
conjugate pair: BH+ (conjugate acid) and B (conjugate base)

34
Q

what is Kw and its units?

A

Kw is the ionic product of water
units: mol2dm-6

35
Q

what is the Kw expression?

A

Kw= [H+][OH-]

36
Q

Describe the ionic product of water, Kw?

A

-the value of Kw is the same (1.00 times 10 to the power of -14 mol2dm-6) in a solution at a given temperature (25 degrees)
-this value changes if the temperature changes
-pure water has an equal concentration of H+ and OH- ions. In other words [H+] = [OH-] therefore when referring to pure water, we can simplify to Kw= [H+]squared

37
Q

what is pH?

A

logarithmic scale that measures the concentration of H+ ions in solution

38
Q

what is the mathematical relationship between pH and the concentration of H+(aq)?

A

pH= -log[H+(aq)]

39
Q

what is the equation to determine the concentration go H+ ions?

A

[H+(aq)] = 10 to the power of -pH

40
Q

How do you calculate the pH of strong monoprotic acids? (e.g HCl and HNO3)

A

monoprotic acids dissociate to produce one H+ ion for every acid molecule. This means the concentration of the acid= the concentration of the H+ ions.

41
Q

How do you calculate the pH of strong diprotic acids? (e.g H2SO4)

A

Diprotic acids dissociate to produce two H+ ions for every acid molecule. This means that the concentration of the acid= 2 x the concentration of the H+ ions

42
Q

How do you calculate the pH of strong bases?

A

-most strong bases dissociate to produce one OH- ion for every base molecule. This means the concentration of the base= the concentration of the OH- ions.
-to work out [H+], use the Kw expression, Kw= [H+][OH-]

43
Q

What assumptions are made when applying the acid dissociation constant, Ka?

A

-assumption 1- only a small amount of the weak acid (HA) dissociates so we can assume that- [HA(aq)]equilibrium=[HA(aq)]start
-assumption 2- the dissociation of acid is greater than the dissociation of water present in the solution. We can assume all the H+ ions come from the acid. [H+(aq)]=[A-(aq)] therefore Ka= [H+]squared/ [HA]

44
Q

What is Ka?

A

acid dissociation constant.
Where HA(aq) (reversible arrow) H+(aq) + Cl-(aq)
Ka= [H+][A-]/ [HA] units: moldm-3

45
Q

What is the problem with using Ka values?

A

it is difficult to compare numbers with negative indices. This problem is solved by converting Ka value into a negative logarithm called pKa.

46
Q

Describe pKa?

A

another way of measuring the strength of an acid similar to pH. The lower the value, the stronger the acid.

47
Q

pKa equation?

A

pKa= -logKa
inverse : Ka=10 to the power -pKa

48
Q

How do you measure pH experimentally?

A

-pH meters are used to measure pH however they must be calibrated correctly
-pH probe must be placed in distilled water first. The meter should be reading pH 7, adjust if not.
-repeat this process with standard solutions at pH 4 and pH 7. Rinse with distilled water between each pH solution.
-wash probe with distilled water after each test

49
Q

what is a conjugate base pair?

A

two species differing by H+

50
Q

what is the Kw value?

A

1 times 10 to the power of -14

Chemistry Alevel OCR YR 13 (13 decks)

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