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CHEM PAPER 1 > ACIDS BASES AND PH > Flashcards

ACIDS BASES AND PH Flashcards

1
Q

Definition of a Bronsted Lowry acid

A

acids are proton donors and they release H+ in water to form H3O+ ions

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2
Q

Definition of a Bronsted Lowry base

A

a proton acceptor that forms OH- ions in water

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3
Q

What is a conjugate acid and base

A

a conjugate acid is a species that gains a proton

a conjugate base is a species that has lost a proton

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4
Q

Kw expression and units

A

Kw = [H+][OH-]

mol2dm-6

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5
Q

Kw constant value and how can it be affected

A

1x10-14 mol2dm-6

unless the temperature changes

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6
Q

Kw expression for pure water

A

Kw = [H+]2

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7
Q

pH equation

A

-log[H+]

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8
Q

How to use pH to figure out concentration of H+

A

10^-pH

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9
Q

How does H+ concentration relate to acid concentration in monoprotic acids

A

H+ concentration = concentration of acid

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10
Q

How does H+ concentration relate to acid concentration in diprotic acids

A

H+ concentration = 2 x acid concentration

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11
Q

2 assumptions of dissociation of weak acids

A
  1. the concentration of acid in equilibrium is roughly equal to the concentration of acid before dissociation
  2. all H+ ions have come from the acid in solution, so [H+] = [A-]
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12
Q

Ka expression for a weak acid

A

Ka = [H+]2 / [HA]

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13
Q

What can we assume at the equivalence point on a titration curve

A

that [H+] = [OH-]

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14
Q

Colour change point of methyl orange

A

pH 3 - 4.5

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15
Q

Colour change point of phenolphthalein

A

pH 8.2 - 10

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16
Q

What is a buffer

A

a chemical that resists a change in pH when small amounts of acid or base are added

17
Q

What is the role of acid buffers and how are they composed

A

resist pH change to keep the solution below pH7

they are made from a weak acid and ITS salt

18
Q

The two equations of an ethanoic acid buffer

A

CH3COOH <–> CH3COO- + H+
(weak acid dissociates weakly so equilibrium lies left)

CH3COO-Na+ <–> CH3COO- + Na+
(salt dissociates strongly so equilibrium lies to the right)

19
Q

What happens when acid is added to an acidic buffer

A

H+ ions will react with the negative ions in solution, there is a high concentration of these from the salt

more weak acid is produced so equilibrium shifts to the left

20
Q

What happens when a base is added to an acidic buffer

A

The OH- ions will react with the H+ ions from the dissociated weak acid

as this removes H+ ions from solution, more H+ ions will be dissociated from the weak acid to counteract the change in concentration

21
Q

What values are needed to calculate pH of a buffer

A

The Ka value
The concentration of the weak acid and its salt

CHEM PAPER 1 (15 decks)

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