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Chemistry A-level > 21 Acids, Bases and Buffers > Flashcards

21 Acids, Bases and Buffers Flashcards

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1
Q

Symbol of concentration

A

Square brackets

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2
Q

pH

A

-log10(H+)

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3
Q

(H+)

A

10^-pH

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4
Q

How to find the alkaline solution

A

Calculate [H+]
Use kw = 1.00x10^-14 to calculate [H+]
Convert [H+] to pH using -log10[H+]

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5
Q

Difference between a strong and weak acid

A

Strong acid is fully desiccated
HCl — H+ + Cl-
NA ⇌ H+ + A-

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6
Q

What type of acid is ethanoic acid

A

Weak acid

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7
Q

Water

A

Little bit of water is ionised at any one time at a constant
(Water is slightly dissociated.)

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8
Q

pH scale

A

Made by Danish biochemist Soren sorenson ( 1909 )

Control of activity

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9
Q

Bronsted-lowry acid

A

An acid is a substance that can donate a proton and base can accept a proton

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10
Q

explain how a solution containing sodium hydrogen carbonate and sodium carbonate can act as a buffer as small amount of acid or alkali are added

A

small amount of acid
-the HCO3- reacts with the added H+, shifting the equilibrium shifts to the left

small amount of alkali
-H+ reacts with the OH- ions shifting equilibrium to the right

the overall amount of H+ stays pretty much the same

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11
Q

state the meaning of the term weak acid as applied to carboxylic acids

A

partially dissociated (partially ionised)

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12
Q

write an equations for the reaction of propanoic acid with sodium carbonate

A

2CH3CH2COOH + Na2CO3 —- 2CH3CH2COOHa + CO2 + H20

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13
Q

suggest what substance might be present in the air to cause the pH to change. Explain how and why the pH of the pH 9.00 solution

A

Carbon Dioxide

The pH was decrease as it has reacted with the H+ ions in solution

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14
Q

suggest a suitable piece of apparatus that could be used to measure out the sodium hydroxide solution. Explain why this apparatus is more suitable than a pipette for this purpose.

A

Buret

you can measure out exactly the right amount of liquid but also you can added it drop by drop

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15
Q

Explain why the end point of this reaction would be difficult to judge accurately using an indicator

A

the pH gradually increase so would be difficult to find the point at which it changes because the indicator could change over a range of values

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16
Q

suggest why choroethanoic acts is a stronger acid than ethnic acid

A

chlorine is more electronegative than hydrogen so withdrawn electrons which weaken the O-H bond

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17
Q

the dissociation of methanol acid in an aqueous solution is endothermic.

Deduce whether the pH of a solution of methanoic acid will increase, decrease or stay the same if the solution is heated. (explain your answer)

A

decrease the pH
if the forwards reaction is endothermic then more product is made to oppose the increase in temperature. the equilibrium shifts to the left.

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18
Q

buffer

A

a buffer solution resist the changes in pH when adding a small amount of acid and alkali

control the pH in living systems

made of weak acid and conjugate base

(A buffer solution maintains an approximately constant pH, despite dilution or addition of small amounts of acid or base.)

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19
Q

Acidic buffer

A

adding alkali
-removes the OH-

adding acid
-equilibrium shifts to the left

20
Q

half-netrlisation

A

pH = pKa

measures of how strong a weak acid is
half way between the starting point and equivalence point
HA + OH- —- H2O + A-

21
Q

acid-base titration

A

titration is used to find the concentration of a solution by gradually adding it to a second solution which it reacts with

22
Q

titration curve

A
  • the pH doesn’t change in the linear manner as a base is added
  • each curve has almost horizontal sections where lots of base is added
  • equivalence point = the point in a titration at which the reaction is just complete
23
Q

Adding an acid (equations)

A

-calculate the pH of the buffer
-calculate the number of moles of acid added
-add the original number of moles of acid
-take this away from the original number of base
-calculate new concentration of acid and salt
-work out the pH
(ignore the small volume as it has little effect on the total volume)

24
Q

Adding a base (equations)

A

-calculate the pH of the buffer
-calculate the number of moles of base added
-add the original number of moles of base
-take this away from the original number of acid
-calculate new concentration of acid and salt
-work out the pH
(ignore the small volume as it has little effect on the total volume)

25
Q

weak acid

A

an acid that is only slightly dissociated into ions in solution

Ka is the dissociation constant for a weak acid
Weak acids and weak bases dissociate only slightly in aqueous solution

26
Q

equivalence point

A

the point in a titration at which the reaction is just complete

27
Q

end point

A

the point in a titration when the volume of reactant added just causes the colour of the indicator to change

28
Q

a H+ in a aqueous solution is always H3O+

A

H+ very small

intenses electric field q

29
Q

ionic product of water

A

little of the water is ionised at any one time
Kw = Kc x [H2O]

Kw = [H+][OH-]

30
Q

acid and alkali

A

H+ + OH- —- salt and water

31
Q

pH scale was inverted

A

1909
Danish biochemist soren Sorenson
control of acidity

32
Q

increase pH

A

more alkali

33
Q

how does a buffer act?

A

buffer solution minimises ph by
HA ⇌ H+ + A-

overall principle
(HA) weak cid removes added alkali
(A-) conjugate base moves added acid

34
Q

addition of an acid

A

[H+] increase
conjugate base reacts with [H+] ions
equilibrium shifts to the left
HA ⇌ H+ + A-

35
Q

addition of alkali

A

[OH-] increase
equilibrium shifts to the right
HA ⇌ H+ + A-

36
Q

buffer in cosmetics

A

natural pH of the skin = 5.5 (protects the skin)

anti-age creams
lower ph than 5.5 - causing the skin to swell - hiding wrinkles

37
Q

half neutralisation

A

pH = pKa

38
Q

calculate buffer

A

Ka = [H+][A-] / [HA]
Ka = [H+]^2 / [HA]
only for a weak acid

39
Q

does Kw increase with temperature ?

A

yes

40
Q

acid

A

proton donator

41
Q

base

A

proton accepter

42
Q

acid- base equilibria

A

involves the transfer of protons

43
Q

pH of hydrogen

A

The concentration of hydrogen ions in aqueous solution covers a very wide range. Therefore, a logarithmic scale, the pH scale, is used as a measure of hydrogen ion concentration.

44
Q

water pH

A

KW = [H+][OH–]

the value varies with temperature

45
Q

pKa =

A

–log10 Ka

46
Q

acidic buffer

A

solutions contain a weak acid and the salt of that weak acid

47
Q

alkali buffer

A

solutions contain a weak base and the salt of that weak base

Chemistry A-level (19 decks)

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