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CHEMISTRY > Acids and Bases > Flashcards

Acids and Bases Flashcards

1
Q

Define a Bronsted- Lowry acid

A

proton donor

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2
Q

Define a Bronsted- Lowry base

A

Proton acceptor

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3
Q

What ion causes a solution to be acidic? (2 answer) Name and formula

A

H+ (hydrogen ion) or, more accurately, H3O+ (oxonium ion), as protons react with H2O to form it

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4
Q

what ion causes a solution to be alkaline?

A

-OH (hydroxide ion)

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5
Q

Write an equation for the ionization of water (2)

A

2 H2O (l) <=> H3O+ (aq) + -OH (aq)
or H2O (l) <=> H+ (aq) + -OH (aq)

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6
Q

Derive Kw using the equation for ionization of water

A

K eq = [H+] [OH-] / [H2O]
[H2O] K eq = [H+] [OH-]

[H2O] is so large compared to [H+] and [OH-] that [H2O]K eq can be considered to be constant. [H2O] K eq = Kw

so,
Kw = [H+][OH-]

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7
Q

What is the value of Kw at 298 K?

A

1.0 x 10^{-14}

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8
Q

What physical factor affect the value of Kw? How do they affect it?

A

Temperature only- if temperature in increased, the equilibrium moves to the right so Kw increases and the pH of pure water decreases

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9
Q

Why is pure water still neutral, even if pH does not equal 7?

A

[H+] = [OH-]

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10
Q

Give an expression for pH in terms of H+

A

pH = -log10 [H+]

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11
Q

What is the relationship between pH and concentration of H+?

A

Lower pH = higher concentration of H+

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12
Q

If two solutions have a pH difference of 1, what is the difference in [H+]?

A

A factor of 10

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13
Q

How do you find [H+] from pH?

A

[H+] = 10 ^{-pH}

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14
Q

How does one find [OH-] from pH? (at 298K)

A

Find [H+], use Kw ( equal to 1 x 10 ^{-14} at 298 K) to calculate [-OH]

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15
Q

What is different when finding [H+] from the concentration of diprotic and triprotic acids?

A

Need to multiply the concentration of the acid by the number of protons to find [H+’

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16
Q

How do you calculate the pH of a strong alkaline solution?

A

Use Kw to calculate [H+] from [OH-]
Use pH = -log [H+]

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17
Q

Define the term strong acid

A

One which fully dissociates in water ( HX => H+ + X-)

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18
Q

Define the term strong base

A

One which fully dissociates in water (XOH => X+ + -OH)

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19
Q

What is the difference between concentrated and strong?

A

Concentrated means many mol per dm^3, strong refers to amount of dissociation

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20
Q

What is a weak acid and a weak base?

A

Weak acids and bases do not fully dissociate in water. They only partially dissociate into their ions

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21
Q

Give some examples of strong acids

A

HCl, H2SO4, H3PO4

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22
Q

Give some examples of strong bases

A

NaOH, CaCO3, Na2CO3

23
Q

Give some examples of weak acids

A

CH3 COOH (ethanoic acid), any organic acid

24
Q

Give some examples of weak bases.

A

NH3

25
Q

What is Ka? (expression)

A

For acid HA, HA <=> H+ + A-

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

26
Q

How would you work out the pH of a weak acid?

A

Use the equation for Ka, subbing in values for [A-] and [HA].

Use pH = -log[H+] equation to find pH

27
Q

What is a titration?

A

The addition of an acid/ base of known titration to a base/ acid of unknown titration to determine the concentration.
An indicator is used to show that neutralization has occurred, as is a pH meter.

28
Q

Draw a diagram of the equipment that could be used for titration.

A

Find the diagram on PMT Acids and Bases slide 57

29
Q

Draw the titration curve for a strong acid with a strong base added

A

Find the correct diagram on PMT slide 59

30
Q

Draw the titration curve for a strong acid with weak base added

A

find the correct diagram on PMT acids and bases slide 61

31
Q

Draw the titration curve for a weak acid with a weak base added

A

Find the correct diagram on PMT slide 62 Acids and Bases

32
Q

Draw the titration curve for a weak acid with a strong base added

A

Find the correct diagram on PMT slide 64

33
Q

Define the term equivalence point

A

The point at which the exact volume of base has been added to just neutralize the acid, or vice-versa

34
Q

What generally happens to the pH of the solution around the equivalence point?

A

There is a large and rapid change in pH, except in weak-weak titration

35
Q

How would you calculate the concentration of a reactant if you know the volume and concentration of the other reactant and the volume of that reactant added

A
  1. calculate mols of one reactant
  2. Use balanced equation to work out mols of the other
  3. Use conc = mol/ vol to calculate concentration
36
Q

What is the end point?

A

The volume of acid or alkali added when the indicator just changes color. If the right indicator is chosen, equivalence point = endpoint

37
Q

what are the properties of a good indicator for a reaction? (3)

A
  1. Sharp color change (not gradual) - no more than one drop of acid/ alkali needed for color change
  2. End point must be the same as the equivalence point, or titration gives wrong answer
  3. Distinct color change so it is obvious when the end point has been reached
38
Q

What indicator would you use for a strong acid-strong base titration?

A

Phenolphthalein or methyl orange, but phenolphthalein is usually used as it has a clearer color change.

39
Q

What indicator would one use for a strong acid-weak base titration?

A

Methyl orange

40
Q

What indicator would one use for a strong base-weak acid titration?

A

phenolphthalein

41
Q

What indicator would one use for a weak acid-weak base titration?

A

Neither methyl orange or phenolphthalein is suitable, as neither give a sharp change at the end point

42
Q

What color is methyl orange in acid? In alkali? At what pH does it change?

A

Red in acid; yellow in alkali. Changes at about pH=4 - 5. Approx. same as pKa value

43
Q

What color is phenolphthalein in acid? in alkali? At what pH does it change?

A

colorless in acid; red in alkali. Changes at about pH= 9 - 10. Approx. same as pKa value.

44
Q

What is the half-neutralization point?

A

When volume = half the volume that has been added at the equivalence point

45
Q

Define a buffer solution

A

A solution that resists changes in pH when small amount of acid/ alkali are added

46
Q

What do acidic buffer solutions contain in general terms?

A

A weak acid and a soluble salt of that acid that fully dissociates

47
Q

Write a reaction for an acidic buffer with added acid

A

A- + H+ => HA, opposes addition of H+

48
Q

Write a reaction for an acidic buffer with added alkali.

A

HA + OH- => H2O + A-

49
Q

How else can one achieve an acidic buffer solution other than just mixing the constituents?

A

Neutralize half of a weak acid ( meaning the acid must be in excess) with an alkali - this forms a weak acid/ soluble salt mixture.

50
Q

What do basic buffer solutions contain in general terms?

A

Weak base and soluble salt of that weak base

51
Q

How can one calculate the pH of buffer solution?

A

Use the Ka of the weak acid, sub in [A- and [HA], calculate [H+] => pH

52
Q

How can one calculate the new pH of a buffer solution when acid or base is added?

A

Calculate number of moles of H+ and A- and HA before acid or base is added. Use equations to work out new moles of A- and HA => find [H+] => pH

53
Q

Which buffer system maintains blood pH at 7.4? What happens when acid/ alkali is added?

A

H+ + HCO3- <=> CO2 + H2O
Add OH- => reacts with H+ to form H2O, then shifts equilibrium left to restore H+ lost
Add H+ => equilibrium shifts to the right, removing excess H+

54
Q

What products are buffers found in?

A

Shampoos, detergents => important to keep pH right to avoid damage to skin, hair, fabrics

CHEMISTRY (11 decks)

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