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Chemistry > 1.12 Acid Base Equilibria > Flashcards

1.12 Acid Base Equilibria Flashcards

1
Q

What is the definition of a Bronsted-Lowry acid?

A

A Bronsted-Lowry acid is defined as a substance that can donate a proton.

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2
Q

What is the definition of a Bronsted-Lowry base?

A

A Bronsted-Lowry base is defined as a substance that can accept a proton.

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3
Q

Give the equation used to calculate pH.

A

pH = -log[H+]

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4
Q

What is the definition of a strong acid?

A

Strong acids completely dissociate.

The concentration of hydrogen ions in a monoprotic strong acid will be the same as the concentration of the acid.

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5
Q

Calculate the pH of 0.1 mol dm-3 HCl.

A

pH = -log(0.1) = 1.00

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6
Q

Always give pH values to 2d.p. in the exam.

A

know this?

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7
Q

Give the equation used to calculate the [H+] from pH.

A

[H+] = 1x10^-pH

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8
Q

Answer the example 1 on page 1 in the chemrevise revision guide.

A

correct?

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9
Q

In all aqeous solutions and pure water, what equilibrium occurs?

Give the equation for Kc.

Give the equation for Kw.

A

(see page 1 in the chemrevise revision guide)

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10
Q

At 25ºc what is the value of Kw?

A

At 25ºc the value of Kw for all aqueous solutions is 1x10^-14 mol2dm-6

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11
Q

What is the Kw expression used for?

A

The Kw expression can be used to calculate [H+ (aq)] ions if we know the [OH- (aq)] ions and vice versa.

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12
Q

Answer example 2 on page 1 in the chemrevise revision guide. (use the information in the box above the question)

A

correct?

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13
Q

What happens if you increase the temperature of the pH of pure water?

A

At different temperatures to 25ºc the pH of pure water changes. Le Chatelier’s principle can predict the change. The dissociation of water is endothermic so increasing the temperature would push the equilibrium to the right giving a bigger concentration of H+ ions and a lower pH.

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14
Q

What is the definition of a strong base?

A

Strong bases completely dissociate into their ions.

e.g. NaOH -> Na+ + OH-

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15
Q

Answer example 3 on page 2 in the chemrevise revision guide.

A

correct?

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16
Q

What is the definition of a weak acid?

A

Weak acids only slightly dissociate when dissolved in water, giving an equilibrium mixture.

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17
Q

Give the expression for Ka.

A

(see page 2 in the chemrevise revision guide)

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18
Q

What is the Ka for ethanoic acid?

A

The Ka for ethnic acid is 1.7x10-5 moldm-3

The larger the Ka the stronger the acid.

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19
Q

Answer example 4 on page 2 in the chemrevise revision guide.

A

correct?

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20
Q

Give the equation for calculating the Ka from the pKa.

A

Ka = 10^-pKa

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21
Q

Give the equation for calculating the pKa from the Ka.

A

pKa = -log(Ka)

22
Q

Answer example 5 on page 2 in the chemrevise revision guide.

A

correct?

23
Q

Answer example 6 on page 2 in the chemrevise revision guide.

A

correct?

24
Q

Answer example 7 on page 3 in the chemrevise revision guide.

A

correct?

25
Q

Answer example 8 on page 3 in the chemrevise revision guide.

A

correct?

26
Q

Answer example 9 on page 3 in the chemrevise revision guide.

A

correct?

27
Q

Answer example 10 on page 3 in the chemrevise revision guide.

A

correct?

28
Q

Answer example 11 on page 4 in the chemrevise revision guide.

A

correct?

29
Q

When a weak acid has been reacted with exactly half the neutralisation volume of alkali, how can the Ka expression be rearranged?

A

(see page 4 in the chemrevise revision guide)

30
Q

How do you calculate the pH of a diluted strong acid?

A

(see page 4 in the chemrevise revision guide)

31
Q

How do you calculate the pH of a diluted base?

A

(see page 4 in the chemrevise revision guide)

32
Q

Answer example 13 on page 4 in the chemrevise revision guide.

A

correct?

33
Q

Give the definition of a buffer solution.

A

A buffer solution is one where the pH does not change significantly if small amounts of acid or alkali are added to it.

34
Q

How is an acidic buffer solutionmade?

A

An acidic buffer solution is made from a weak acid and a salt of that weak acid (made from reacting the weak acid with a strong base)

e.g. ethanoic acid and sodium ethanoate.

35
Q

How is a basic buffer solution made?

A

A basic buffer solution is made from a weak base and a salt of that weak base (made from reaction the weak base with a strong acid)

e.g. Ammonia and ammonium chloride.

36
Q

If you add small amounts of acid to a buffer how does the pH stay fairly constant? What happens?

A

(see page 5 in the chemrevise revision guide)

37
Q

If you add small amounts of alkali to a buffer how does the pH stay fairly constant? What happens?

A

(see page 5 in the chemrevise revision guide)

38
Q

Answer example 14 on page 6 in the chemrevise revision guide.

A

correct?

39
Q

Answer example 15 on page 6 in the chemrevise revision guide.

A

correct?

40
Q

Answer example 16 on page 6 in the chemrevise revision guide.

A

correct?

41
Q

When you add a small amount of alkali to a buffer, what happens to the moles of the buffer acid?

A

If a small amount of alkali is added to a buffer then the moles of the buffer acid would reduce by the number of moles of alkali added and the moles of salt would increase by the same amount so a new calculation of pH can be done with the new values.

42
Q

When you add a small amount of acid to a buffer, what happens to the moles of the buffer salt?

A

If a small amount of acid is added to a buffer then the moles of the buffer salt would reduce by the number of moles of acid added and the moles of buffer acid would increase by the same amount so a new calculation of pH can be done with the new values.

43
Q

Answer example 17 on page 7 in the chemrevise revision guide.

A

correct?

44
Q

Describe the method of an experiment you would use to construct a pH curve.

A

(see top of page 8 in the chemrevise revision guide)

45
Q

Draw the general pH curve for a strong acid titrated with a strong base.

A

(see page 8 in the chemrevise revision guide)

46
Q

Draw the general pH curve for a weak acid titrated with a strong base.

A

(see page 8 in the chemrevise revision guide)

47
Q

Draw the general pH curve for a strong acid titrated with a weak base.

A

(see page 9 in the chemrevise revision guide)

48
Q

Draw the general pH curve for a weak acid titrated with a weak base.

A

(see page 9 in the chemrevise revision guide)

49
Q

What is the half equivalence point on a pH curve?

A

The equivalent point lies at the mid point of the extrapolated vertical portion of the curve.
(see page 8 in the chemrevise revision guide for an example)

50
Q

Write the Kw expression for pure water.

A

(see page 1 in the chemrevise revision guide)

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