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acids, bases and buffers Flashcards

1
Q

define a bronsted-lowry acid

A

a proton donor

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2
Q

define a bronsted-lowry base

A

a proton acceptor

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3
Q

define a lewis acid

A

electron pair acceptor

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4
Q

define a lewis base

A

electron pair donor

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5
Q

what ion causes a solution to become acidic? give their names and formulas

A

H+ (hydrogen ion)

H3O+ (oxonium ion)

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6
Q

what ion causes a solution to be alkaline?

A

OH- (hydroxide ion)

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7
Q

write an equation for the ionisation of water (2)

A

2H2O (l) ⇌ H3O (aq) + OH- (aq)

H2O (l) ⇌ H+ (aq) + OH- (aq)

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8
Q

give an example of a monobasic acid

A

HCl

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9
Q

give an example of a dibasic acid

A

H2SO4

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10
Q

what is a monobasic acid?

A

a monobasic acid releases 1 mole of H+ ions for every 1 mole of acid

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11
Q

what is dibasic acid?

A

a dibasic acid releases 2 moles of H+ ions for every 1 mole of acid

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12
Q

what is a tribasic acid?

A

a tribasic acid releases 3 moles of H+ ions for every 1 mole of acid

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13
Q

give an example of a tribasic acid

A

H3PO4

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14
Q

name examples of strong acids

A
  1. HCl (hydrochloric acid)
  2. HNO3 (nitric acid)
  3. H2SO4 (sulfuric acid)
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15
Q

name examples of weak acids

A
  1. H3PO4 (phosphoric acid)
  2. HF (hydrofluoric acid)
  3. CH3COOH (methanoic acid)
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16
Q

identify the acid-base pairs for the reaction below:

CH3COOH + H2O ⇌ CH3COO- + H3O+

A

CH3COOH = acid 1

H2O = base 2

CH3COO- = base 1

H3O+ = acid 2

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17
Q

define a strong acid

A

an acid that fully dissociates in solution to produce H+ ions

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18
Q

what is the difference between concentrated and strong?

A

concentrated means many moles per dm3, strong refers to the amount of dissociation

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19
Q

define weak acids

A

acids that only partially dissociate in solution to H+ ions, they remain in equilibrium

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20
Q

what is the constant that is used to measure the extent of acid dissociation called?

A

acid dissociation constant

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21
Q

what is the symbol of acid dissociation constant

A

Ka

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22
Q

write the acid dissociation constant expression for:

Ha ⇌ H+ + A-

A

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

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23
Q

what does a large Ka value mean

A

the larger the Ka the greater the extent of dissociation

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24
Q

write the equation used to convert Ka into pKa

A

pKa = -log10Ka

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25
write the equation that is used to convert pKa into Ka
Ka - 10^-pka
26
what is the relationship between pKa and the strength of the acid
smaller the pKa the stronger the acid
27
write the equation used to convert concentration of H+ into pH
pH = -log[H+]
28
write the equation used to convert pH into concentration of H+
[H+] = 10^-pH
29
why is a pH scale useful compared to the concentration of H+
pH scale allows a wide range of H+ concentration to be expressed as simple positive values
30
what is the relationship between pH and [H+]
high pH value means small [H+]
31
if two solutions have a pH difference of 1, what is the difference in [H+]?
a factor of 10
32
[H+] of a strong acid is equal to what?
[H+] = [HA]
33
write the equation used to calculate [H+] of weak acids
[H+] = √Ka x [HA]
34
what is the assumption made when calculating pH of a weak acid?
- the **concentration of acid at equilibrium is equal to the concentration of acid after dissociation** - this is because very little of the acid dissociates
35
write the expression for ionic product of water, Kw
Kw = [H+][OH-]
36
what are the units for Kw
mol2dm-6
37
what is the value of Kw at 298K?
1x10^-14
38
what physical factors affect the value of Kw? how do they affect it?
temperature only if temperature is increased the equilibrium moves to the right so the Kw increases and the pH of pure water decreases
39
indices of [H+] and [OH-] always add up to what value?
-14
40
define the term strong base
bases that dissociate completely in water to release OH-
41
give examples of some strong bases
1. NaOH (sodium hydroxide) 2. KOH (potassium hydroxide) 3. Ca(OH)2 (calcium hydroxide)
42
give examples of some weak bases
NH3 (ammonia)
43
write the equation used to calculate the [H+] of some strong bases
[H+] = Kw / [OH-]
44
define a buffer solution
a mixture that minimises pH change on addition of small amounts of an acid or base
45
what are the 2 ways in which buffers can be made
- weak acid and its conjugate base - weak acid and a strong alkali
46
in which direction does the equilibrium shift when an acid is added to a buffer solution? why?
- equilibrium shifts to the left - because [H+] increases - conjugate base reacts with [H+] to remove most of the [H+]
47
in which direction does the equilibrium shift when an alkali is added to a buffer solution? why?
- equilibrium shifts to the right - because [OH-] increases - small concentration of H+ reacts with OH- to restore the H+ ions, HA dissociates shifting the equilibrium
48
write the equation used to calculate [H+] of buffer solution
[H+] = Ka x [Ha]/[A-]
49
which buffer system maintains blood at 7.4? what happens when acid/alkali is added?
H+ + HCO3 ⇌ CO2 + H2O - Add OH- = reacts with H+ to form H2O, then shifts equilibrium left to restore the H+ lost - Add H+ = equilibrium shifts to the right, removing excess H+
50
what is a titration?
the addition of an acid/base of known concentration to base/acid to determine the concentration, an indicator is used to show that neutralisation has occurred
51
list the equipment that can be used in a titration experiment
1. clamp stand 2. white tile 3. burette 4. pipette and filler 5. conical flask 6. acid/alkali of known concentration (goes into burette) 7. acid/alkali of unknown concentration (goes into conical flask)
52
define the term equivalence point
the point at which the exact volume of base has been added to just neutralise the acid
53
what is the end point?
the point at which pH changes rapidly
54
what are the properties of a good indicator for a reaction?
- sharp colour change = no more than 1 drop of alkali/acid needed for colour change - end point must be the same as the equivalence point - distinct colour change so it is obvious when end point is reached
55
what indicator would you use for a strong acid - strong base titration
phenolphthalein or methyl orange
56
what indicator would you use for a strong acid - weak base titration
methyl orange
57
what indicator would you sue for a strong base - weak acid titration
phenophalein
58
what indicator would you sue for a weak base - weak acid titration
- neither methyl orange or phenophalein is suitable - neither give a sharp change at the endpoint
59
what colour is methyl orange in acid, alkali and the end point?
acid = red alkali = yellow end point = yellow
60
what colour is phenophalein in acid, alkali and the end point?
acid = colourless alkali = pink end point = colourless
61
describe how you would use a ph metre
- remove pH probe from storage solution and rinse with distilled water - dry probe and place into solution of unknown pH - let pH probe stay in solution until it gives a settled reading

chemistry (37 decks)

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