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Chemistry unit 4 > 4.3 Acids and Bases > Flashcards

4.3 Acids and Bases Flashcards

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1
Q

What is a hydrogen ion identical to?

A

H+ is identical to a proton

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2
Q

What is the Bronsted-Lowry definition of an acid?

A

A proton donor

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3
Q

What is the Bronsted-Lowry definition of a base?

A

A proton acceptor

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4
Q

What does “amphoteric” mean?

A

Can act as both an acid and a base

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5
Q

According to the Bronsted-Lowry theory, when is an acidic substance an acid?

A

When a base is present

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6
Q

What is an example of an amphoteric substance?

A

Water

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7
Q

What is a conjugate acid formed from?

A

Formed from the ions of the base

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8
Q

What pH numbers do acidic solutions have?

A

Less than 7 at 25C

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9
Q

What is the pH of a neutral solution?

A

7 at 25C

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10
Q

What pH numbers do basic solutions have?

A

Greater than 7 at 25C

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11
Q

What is the equation for pH?

A

pH = -log[H+]

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12
Q

What is the equation for [H+]?

A

[H+] = 10^(-pH)

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13
Q

What is a strong acid?

A

A strong acid is fully dissociated in solution

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14
Q

Why is HCl said to be monoprotic?

A

Because each molecule can donate just one proton

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15
Q

Why is H2SO4 said to be diprotic?

A

Because each molecule can donate two protons

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16
Q

What is the hydrogen ion concentration in 2.0M sulphuric acid?

A

4.0M

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17
Q

What is a strong base?

A

A strong base is fully dissociated in solution

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18
Q

What is the equation for Kw?

A

Kw = [H+][OH-]

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19
Q

What is the value of Kw at 25C?

A

1 x 10^(-14)

20
Q

How can Kw be rewritten for pure water?

A

Kw = [H+]^2

21
Q

How can Kw be rearranged to find [H+] of pure water?

A

[H+] = √(Kw)

22
Q

What happens to the value of Kw as temperature increases? Why?

A

Kw increases as temperature increases due to the dissociation of water being endothermic

23
Q

What are weak acids and bases?

A

Weak acids and bases are partially dissociated in aqueous solution

24
Q

What is Ka?

A

Ka is the acid dissociation constant

25
Q

What is the equation for Ka?

A

Ka = ([H+][A-]) / ([HA])

26
Q

What is the equation for pKa?

A

pKa = -log(Ka)

27
Q

Why must Ka be taken into account when working out the pH of weak acids?

A

Because you cannot assume that the hydrogen ion concentration is the same as the acid concentration, due to it not dissociating fully

28
Q

How can Ka be rewritten for a weak acid?

A

Ka = [H+]^2 / [HA]

29
Q

How can Ka of a weak acid be rewritten to find [H+]?

A

[H+] = √(Ka X [HA])

30
Q

What are acid-base titrations used to find out?

A

They are used to find out the volumes needed to create a neutral solution

31
Q

What is a pH curve?

A

The graph of pH against volume of acid or base to create a neutral solution

32
Q

When does the equivalence point occur when the titration involves monoprotic acids and bases?

A

When there are equimolar amounts of acid and base present

33
Q

Where is the equivalence point with a strong acid into a strong base?

A

pH 7.0

34
Q

Where is the equivalence point with a strong acid into a weak base?

A

Below pH 7.0

35
Q

Where is the equivalence point with a weak acid into strong base?

A

Above pH 7.0

36
Q

Where is the equivalence point with a weak acid into weak base?

A

pH 7.0

37
Q

What are acid-base indicators?

A

Acid-base indicators are weak organic acids or bases

38
Q

Why is universal indicator unsuitable for use in titrations?

A

It is a mixture of four different indicators, giving it a range of different colours

39
Q

What is the general equation for an indicator?

A

HIn (aq) H+ (aq) + In- (aq)

40
Q

Only when will an indicator be effective in a particular indicator?

A

When its pH range matches the change in pH at equivalence

41
Q

What is the definition of a buffer?

A

A solution which resists small changes in pH when small amounts of acid or base are added to it, or when it is diluted

42
Q

What are some applications of buffers?

A
  • to calibrate pH meters
  • to stop enzymes denaturing after being extracted
  • to achieve the correct conditions for dying fabrics
  • in shampoo to make the hair look smooth and shiny
43
Q

What does an acidic buffer contain?

A

A weak acid and its conjugate base

44
Q

What does a basic buffer contain?

A

A weak base and its conjugate acid

45
Q

What is the equation for working out the [H+] of a buffer?

A

[H+] + Ka x ([HA] / [A-])

Chemistry unit 4 (12 decks)

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