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Chemistry module 5 > acids, bases and pH > Flashcards

acids, bases and pH Flashcards

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1
Q

What are acids

A

dissociate and release H+ ions in an aqueous solution

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2
Q

What are alkalis

A

dissociate and release OH- ions in aqueous solution
it is also a soluble base

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3
Q

Wat is the ionic equation for a neutralisation reaction

A

H+(aq) + OH-(aq) -> H2O(l)

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4
Q

What is a bronsted lowry acid

A

proton donor

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5
Q

What is a bronsted lowry base

A

proton acceptor

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6
Q

What is the equation for the dissociation of hydrochloric acid

A

HCl(l) reversible arrow H+(aq) +OH-(aq)

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7
Q

Why can an equilibrium sign show dissociation of HCl even though it is a strong acid

A
  • equilibrium is well to the right hand side
  • a single arrow can be used to indicate that the forward reaction effectivley goes to completion
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8
Q

What are HCl and Cl-

A

are a conjugate acid base pair

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9
Q

What is a conjugate acid base pair

A
  • contains two species that can be interconverted by transfer of a proton
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10
Q

Describe how HCl forms it conjugate acid base pair

A
  • in forward direction HCl releases a proton to form its conjugate base Cl-
  • in the reverse direction Cl- accepts a proton to form its conjugate acid HCL
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11
Q

Describe the dissociation of HCl in a neutralisation reaction

A

forward direction
HCl is an acid as it donates H+
OH- is a base a it accepts H=
reverse direction
H2O is an acid as it donates H+
Cl- is a base as it accepts H+

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12
Q

What is the equation for neutralisation of HCl and name the ocnjugate acid base pairs

A

HCl(aq) + OH- (aq) reversible sign H2O (l) + Cl-
HCl = acid 1
Oh- =base 2
H2O =acid 2
CL- = base 1

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13
Q

In an aqueuous solution what does dissociation require

A

a proton ot be transferred from an acid to a base

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14
Q

What are the requirement for dissociation to occur

A

does not take place unless water is present

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15
Q

What is the equation for HCl and H2O and state the conjugate acid base pairs

A

HCl (aq) + H2O(l) reversible sign H3O+(aq) +Cl (aq)
HCl =acid 1
H2O = base 2
H3O+ =acid 2
Cl- =base 1

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16
Q

How is hydronium ion formed and where is it important

A
  • H2O has accepted a proton to form its conjugate acid the hydronium ion H3O+(aq)
  • important as it is the active acid ingredient in any aqueous acid
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17
Q

What are the two neutralisation equations

A

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

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18
Q

What do monobasic, dibasic and tibasic acids refer to

A

the total number of hydrogen ions in the acid that can be replaced per molecule in an acid base reaction
typically replacement of protons by metal ions or ammonium ions to form a salt

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19
Q

what happens to the volume of alkali with increasing number of hydrogen

A

as number of hydrogen increases the volume increases by the same amount
2[H+] - volume doubles

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20
Q

How do you form an ionic equation

A
  • write out full equation
  • cancel spectator ions
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21
Q

What are spectator ion

A

ions that do not change during the reaction
in equations they can simply be cancelled out

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22
Q

What do dilute acids undergo with some metals and write the equation

A

redox reactions
acid + metal -> salt + hydrogen

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23
Q

What are carbonates an example of

A

a base

24
Q

what do carbonates form when reacting with acid and what type of reaction is it

A

neutralisation
acid + carbonate -> salt + water + carbon dioxide

25
Q

What is formed with the reaction of acids and metal oxides/ hydroxides and what reaction is this

A

neutralisation
acid + base -> salt +water

26
Q

What type of reaction is acids with alkalis and write the equation

A

neutralisation
acid + alkali -> salt + water

27
Q

What was the test before figuring out the pH scale

A
  • measured as colours using indicators
28
Q

What is a more accurate way than using pH indicator paper or universal indicator

A
  • pH probe
  • measuring hydrigen ions using an electrochemical cell
29
Q

What is the advantage of using pH indicator paper or universal indicator

A

easier and cheaper

30
Q

What does a low value of H+ show

A

high value of pH

31
Q

what does a high value of H+ show

A

low value of pH

32
Q

What is the equation to find out pH

A

-log[H+]

33
Q

How do you find out [H+]

A

10^-pH

34
Q

What happens to the hydrogen ion concentration as the pH goes up by one

A

10 times increase

35
Q

What is the equationfor a strong monobasic acid HA

A

HA(aq) -> H+(aq) + A-(aq)

36
Q

What is the hydrogen concentration equal to for a strong acid

A

[H+]=[HA]

37
Q

How is the pH of a strong acid calculated

A

concentration of an acid

38
Q

What are the steps for calculating pH form acid concentration

A
  • convert [HA] into [H+]
  • use calculator to find pH
39
Q

What are the steps for calculating acid concentration from pH

A
  • use calculator to find [H+]
  • convert [H+] into [HA]
40
Q

What are the steps for calculating pH changes on dilution

A
  • find concentration of diluted acid
  • find pH values before and after dilution
41
Q

What is a strong acid

A

it completley dissociates in an aqueous solution

42
Q

What is a weak acid

A

partially dissociates in an aqueous solution

43
Q

What is Ka

A

acid dissociation constant
shows acid strength

44
Q

What is the equation for the dissociation of a weak acid

A

HA reversible sign H+ + A-

45
Q

What are the units for Ka

A

moldm-3

46
Q

What is the equation for Ka

A

[H+][A-]/HA]

47
Q

What does Ka change with and describ how

A

temperature
larger numerical value of Ka the further equilbrium is to the right
larger Ka value greater the dissociation and greater the acid strength

48
Q

What is the equation for PKa and hence what is the equation for Ka

A

PKa=-logKa
Ka=10^-pKa

49
Q

Describe the trend with the strength of acid,Ka and PKa

A

the stronger the acid the larger the Ka value and the smaller the pKa value
the weaker the acid the smaller the Ka value and the larger the pKa value

50
Q

What are pka values used for

A

comparing strengths of weak acids particularly in biological systems

51
Q

what does [H=] depend on in a weak acid

A

concentration of acid [HA]
Ka acid dissociation constant

52
Q

How is the Ka expression simplified for calculations

A

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

53
Q

What are the two approximations when calculating concentrations of pH of a weak acid

A

Ha dissociates to produce equilibrium concentrations of H+ and A- that are equal also be a very small concentration of H+ from the dissociation of water but thi will be extremley mall and can be neglected compared with the H+ concentration from the acid
[H+]=[A-]
equilibrium concentration of HA is smaller than the undissociated concentration the dissociation of weak acids is small [Ha]»[H+] and can neglect any decrease in concentration of HA from dissociation [HA]equilibrium=[HA] start

54
Q

How do you calculate pH of a weak acid

A

calculate [H+] from Ka and [HA]
use calculator to find pH

55
Q

How is Ka determined for a weak acid eperimentally

A

preparing a standard solution of the weak acid of known concentration
measuring pH of a standard solution using a pH meter

56
Q

How is Ka calculated for a weak acid

A

use calculator to find [H=}
calculate Ka from [H+] and [HA]

57
Q

What are the approximations in calculations involving weak acids

A
  • dissociation of water is negligble
  • [H+] - [A-]
  • [H+] from the dissociation of water will be significant compared with dissociation of the eak acid this approximation breaks down for vry weak acids or very dilute solutions
  • concentration of acid is much greater than h+ concentration at equilibrium
  • [HA] equilibrium={HA] start
  • this approxumation holds for weak acid with small kA values breaks down when [H+] becomes significant and there is a real difference [HA]equilibrium and [HA] start - [H+] equilibrium
  • approximation is not justified for stronger weak acids with Ka.10^-2 and for very dilute solutions

Chemistry module 5 (3 decks)

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