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chemistry > 21 acids and bases > Flashcards

21 acids and bases Flashcards

1
Q

define acid

A

proton donor

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2
Q

define base

A

proton acceptor

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3
Q

define a strong acid

A

an acid that fully dissociates

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4
Q

define a weak acid

A

an acid that only partially dissociates

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5
Q

define pH

A

-log10[H+]

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6
Q

how do you calculate the concentration of H+ ([H+]) from pH?

A

10^-pH

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7
Q

what does Kw mean?

A

the ionic product of water

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8
Q

define Kw

A

[H+][OH-]
1x10^-14

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9
Q

what is a monoprotic acid?

A

one which only releases one H+ ion

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10
Q

what is a diprotic acid?

A

one which releases two H+ ions

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11
Q

if the pH is small, what does that mean in terms of concentration of H+ ions?

A

greater concentration of H+ ions

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12
Q

name 4 strong acids

A

HCl (hydrochloric acid)
H2SO4 (sulfuric acid)
HNO3 (nitric acid)
H3PO4 (phosphoric acid)

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13
Q

how does HCl dissociate?
give an equation

A

fully dissociates
HCl –> H+ + Cl-

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14
Q

where does the equilibrium lie in equations of strong acid dissociations?

A

entirely to the right

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15
Q

if the concentration of HCl is originally 2moldm-3, what will be the conc of H+ once fully dissociated?

A

2moldm-3

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16
Q

if the concentration of H2SO4 is originally 2moldm-3, what will be the conc of H+ once fully dissociated?

A

4moldm-3

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17
Q

how does a weak acid dissociate?
give an equation in terms of HA

A

partially dissociates
HA <–> H+ + A-

18
Q

where does the equilibrium lie in equations of weak acid dissociations?

A

on the left hand side

19
Q

write a Ka expression for the dissociation of weak acid HA

A

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

20
Q

how would you find the concentration of H+ in a weak acid dissociation?

A

[H+] = [A-]
Ka = [H+]^2/[HA]
[H+]^2 = Ka x [HA]
[H+] = √Ka x [HA]

21
Q

how do you calculate pKa?

A

-log10Ka

22
Q

how do you find Ka from pKa?

A

10^-pKa

23
Q

write an equation for the ionisation of water

A

H2O <–> H+ + OH-

24
Q

where does the equilibrium lie in the equations for the ionisation of water?

A

very far left

25
Q

what is the value of Kw?

A

1x10^-14 mol2dm-6

26
Q

give the expression of Kw

A

Kw = [H+][OH-]

27
Q

what affects the value of Kw?

A

temperature

28
Q

why is pure water always neutral?

A

because [H+[ and [OH-] are equal at all times

29
Q

how would you calculate the concentration of pure water?

A

H2O <–> H+ + OH-
[H+] = [OH-]
[H+]^2 = Kw
[H+] = √Kw

30
Q

is the forward reaction of water dissociation endothermic or exothermic?

A

endothermic

31
Q

why does [H+] = 1x10^-7 moldm-3 at 298K?

A

√1x10^-14 = 1x10^-7

32
Q

which way does equilibrium shift when temperature increases in water dissociation?

A

shifts to the right in the endothermic direction to oppose the increase in temperature

33
Q

when a strong base reacts with an acid what does it form?

A

water

34
Q

use NaOH to write an equation to show how a strong base dissociates

A

NaOH –> Na+ + OH-

35
Q

where does the equilibrium lie in a strong base dissociation?

A

entirely to the right

36
Q

how would you calculate the [H+] in a strong alkali? (use NaOH)

A

[NaOH] = [OH-]
Kw = [OH-][H+]
[H+] = Kw/[OH-]

37
Q

define buffer

A

a solution that can resist changes in pH when a small amount of acid or base is added

38
Q

what is an acidic buffer?

A

made of a weak acid and a soluble salt of that acid. maintains a pH below 7

39
Q

what is a basic buffer?

A

made of weak base and a soluble salt of that base. maintains a pH over 7

40
Q

why can buffers only cope with small amounts of acids or bases being added?

A

because can they can become too saturated

41
Q

how would you calculate [H+] in an acidic buffer solution if you are given the concentration of the acid and the salt?

A
  1. construct an equation for the weak acid.
  2. construct a Ka expression for the weak acid.
  3. substitute the values into the expression (HA is the acid A- is the salt)
  4. rearrange the equation to find [H+]
42
Q

how would you calculate [H+] in an acidic buffer solution if you are given the concentration and the volumes of the reactants?

A
  1. construct a neutralisation reaction.
  2. complete an ICE box to figure out the moles
  3. construct a Ka expression for the dissociation of the acid.
  4. rearrange the equation.

chemistry (34 decks)

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