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alevel chem year 2 > Acids, bases and buffers > Flashcards

Acids, bases and buffers Flashcards

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1
Q

Bronsted lowry acid

A

Proton donors, releasing H+ ions into a solution. Alwyas combine with h20 to form hydroxonium ions H30+

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2
Q

Bronsted lowry base

A

Proton acceptors

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3
Q

Alkali

A

A base that dissolved in water, releasing OH- ions

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4
Q

Hydroxonium ions

A

H30+

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5
Q

Monobasic acids

A

Give away one hydrogen

E.g. HCL

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6
Q

Dibasic acids

A

Give away two hydrogens

E.g. H2SO4

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7
Q

Tribasic acids

A

GIve away three hydrogens

E.g. H3PO4

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8
Q

What are conjugate pairs

A

Species that are linked by the transfer of a proton
Always on opposite sides of teh equation
The speies that lost a proton = conjugate base and the species that gained a proton is the conjugate acid

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9
Q

Outline the acid base theory and how its changed

A

Early ideas of acids being sour and alkalis from plant ahes
Base+ acid= solid form
Acids contain hydrogen that can be replaced by metal
ACids form H+ ions and bases form OH- ions
Acid base reactions tranfer protons, H+, An acid donates a proton and a base accepts a proton

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10
Q

Metal+ acid

A

Salt adn hydrogen
The metal atoms donate electrons to teh H+ ions in the acid solution
Metal oxidised and ydrogen reduced

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11
Q

Carbonates+ acid

A

Co2 and h20

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12
Q

Metal oxides( most insoluble bases)+ acids

A

H20 and salt

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13
Q

The pH scale- devised by who?

A

Soren Soreenson

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14
Q

Strong acids

A

Completely dissociate

The conc of H+ ions is therefore the same as the conc of the acid

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15
Q

Converting H+ conc to pH

A
  • log
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16
Q

Converting pH to H+ conc

A

shift log -

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17
Q

pH of a diluted strong acid?

A

h+= H+ old * new vol/old vol

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18
Q

if you have a diprotic acid and are finding conc of h+ from ph?

A

divide by 2

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19
Q

WEak acids

A

Partially dissociate

Equilitbirum mixture

20
Q

What is used for weak acids adn finding equilibium

A

Ka= H+ * A_

/ HA - for diprotic, h+ squared

21
Q

THe larger the Ka value…

A

Th further the equilibrium is to the right and hte ggreater the dissociation and acid strength

22
Q

pKa

A

Making Ka into a whole number
-logka = pka
ka= shift log - pka

23
Q

Stronger acid=……. ka =……. pka

A

Larger ka value

Smaller pKa value

24
Q

What are teh 2 assumptions amde for calculating Ka

A

h+= A-
only small amounts of h+ from dissociation of water

Ha( equilibrium)= HA (start)
equ is smaller , but dissociation is small

25
Q

Ka simplified

A

H+= square root of

KA* HA

26
Q

finding the pH of a strong base?

A

Kw= H * OH

27
Q

What is the value of Kw at 25 degrees

A

1* 10 -14

28
Q

What is Kw called

A

IOnic product of water

29
Q

pH of a diluted base

A

OH-= oh old * old/new volume

H+= kw/oh

30
Q

What can you use to remove added acid AND alkali

A

ethanoic acid
CH3COOH— H+ + CH3COO-

ACt as 2 resevoirs that are a le o act inependently to remove aka and acd

31
Q

Buffer solutions

A

A system that minimises pH changes when small amounts of acid or base are added
Contains 2 components to remove added acid or alkali

32
Q

WEak acid and conjugate base - role of buffers

A

The weak acid remoes added alkali

The conjugate base removes added acid

33
Q

WHat are the 2 ways you can prepare acid buffer solutions

A

Preparation from a weak acid and its salt

Weak acid and a strong akali, partial neutralization

34
Q

Preparation from a weak acid and its salt - buffer

A

The salt fully dissociated and the weak acid only slightly dissoccaites
e.g. ethanoic acid and sodium ethanoate

35
Q

Weak acid and a strong alkali - buffer making

A

NEUTRLISATION
Add an aqueous solution of alklai, such as NaOH, to an excess of the weak acid
The weak acid is partially neutralised by the alkali, forming the conjugate base. Some of the weak acid is left over unreacted. The resulting solution contains a mixture of a salt of the weak acid and any unreacted weak acid

36
Q

What does the buffer equilibrium solution contain

A

UNdissociated acid(HA)
Lots of teh acids conjugate base( a-)
Enough h+ ions to make the solution acidic

37
Q

What happens when acid is added to buffer solution

A

H+ increases
H+ ions react with the conjugate base, A-
The equilibrium shifts to the left, removing most of the H+ ions

38
Q

When alkali is added o buffer solution

A

OH- increases
The small concentration of H+ ions reacts with the oh ions( =h20)
HA dissociates shifting the equilibrium to the right to restore the H+ ions

39
Q

When are buffers most effectie

A

WHne there are equal concentrations of the weak acid and its conjugate base
HA= A-

40
Q

teh pH of the buffer solution=

A

The pKa value of HA

41
Q

Calculating pH value of a buffer

A

The salt of the conjugate base is fully dissociated- equilibrium conc of A- is the same as intitial conc of the salt
HA is only slightly dissociated, so assume that its equilibirum concentration is the same as its intial conc

H+= ka* HA/a- ( weak acid conc/base conc) then -log

42
Q

What pH does the blood plasma need to be

A

between 7.35 and 7.45

43
Q

What happens if blood plasma falls below region it needs to be

A

Acidosis

44
Q

What happens if blood plasma GOES ABOVE region it needs to be

A

Alkaliosis

45
Q

What is the buffer called for blood

A

carbonic acid hydrogen carbonate

H2CO3

46
Q

Addition of H+- in the blood

A

H+ increases
H+ ions react wiht conjugate base, HCo3-
The equilbrium shifts to the left, removing most H+ ions

H2co3— H+ + Hco3

47
Q

On addition of OH- in the blood

A

OH- increases
The small concs of H+ ions reacts with the OH- ions
The h2Co3 dissociates, shifting the equilibirum position ot the RIGHT to restore most of the H+ ions

alevel chem year 2 (7 decks)

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