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physical chemistry > Acids and Bases > Flashcards

Acids and Bases Flashcards

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1
Q

What is a Brønsted-Lowry acid?

A

a proton donor

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2
Q

What is a strong Brønsted-Lowry acid?

A

a fully dissociated proton donor

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3
Q

What is the equation for a strong acid?

A

HX (aq) –> H+(aq) + X- (aq)

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4
Q

What are examples of strong acids?

A

HCl, HNO3, H2SO4 (diprotic)

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5
Q

What is the equation for a weak acid?

A

HX (aq) ⇌ H+(aq) + X- (aq)

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6
Q

What are examples of weak acids?

A

carboxylic acids

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7
Q

Mono, di, and triprotic examples?

A

-carboxylic acids
-dicarboxylic acids
-H3PO4

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8
Q

What are Brønsted-Lowry bases?

A

proton acceptors

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9
Q

What are strong Brønsted-Lowry bases?

A

every base particle will accept/gain a proton

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10
Q

What are weak bases?

A

NH3, Mg(OH)2, Ca(OH)2

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11
Q

What are strong bases?

A

NaOH. (Sr(OH)2, Ba(OH)2

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12
Q

What are weak Brønsted-Lowry bases?

A

only some particles accept/gain a proton

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13
Q

What is pH?

A

pH = -log [H+]

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14
Q

How do you calculate [H+]?

A

[H+] = 10 ^ -pH

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15
Q

What is a property of water?

A

it is very weakly dissociated

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16
Q

What is the equation for water?

A

H2O(l) ⇌ H+(aq) + -OH(aq)

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17
Q

Which way does the equilibrium for water lie?

A

wayyyyy to the left

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18
Q

What type of reaction is the dissociation of water?

A

endothermic because energy is required to break O-H bonds

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19
Q

Why is water neutral?

A

[H+] = [-OH]

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20
Q

Why don’t we include [H20] in the equation?

A

because the [H20] is virtually constant

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21
Q

Why does the pH of water increase as temperature increases?

A

equilibrium shifts to the right to oppose the increase in temperature, which causes an increase in [H+], meaning pH decreases/lowers

22
Q

What is Kw?

A

Kw = [H+] [-OH] - the ionic product of water

23
Q

What is Kw at room temp?

A

1.00 x 10 ^-14

24
Q

What is Kw when you have [H+]?

A

[H+] = √Kw

25
Q

How do you calc the pH of a weak acid?

A

Ka = [H+] [HA-] / [HA] , [H+] = √ Ka x [HA] , pH = -log[H+]

26
Q

How do you calc the pH of a strong base?

A

Kw = [H+] [-OH] , [H+] = Kw / [-OH] , pH = -log[H+]

27
Q

Calc the pH of a SASB solution?

A

-mol acid
-mol base
-excess moles
-[H+] = excess moles / TOTAL volume
-pH = -log[H+]

28
Q

What is an indicator?

A

a substance which changes colour over a narrow pH range

29
Q

Talk about phenolpthalein

A

protonated —— pH 9 —— deprotonated
colourless —— —— —— pink

30
Q

Talk about methyl orange

A

protonated —— pH 4 —— deprotonated
red —— —— —— —— yellow

31
Q

What are the 4 types of pH curves?

A

SASB, WASB, SAWB, WAWB

32
Q

What makes something a strong acid on a graph?

A

starts below pH = 2

33
Q

What makes something a weak acid on a graph?

A

starts above pH = 2

34
Q

What makes something a strong base on a graph?

A

ends above pH = 12

35
Q

What makes something a weak base on a graph?

A

ends below pH = 12

36
Q

Where is v-equivalence on a graph?

A

where the straight part goes down

37
Q

Where is half equivalence on a graph?

A

halfway to where the straight part goes down

38
Q

What indicator for SASB?

A

phenolphthalein and methyl orange as both change colour on the vertical part of the graph

39
Q

What indicator for WASB?

A

phenolphthalein

40
Q

What indicator for SAWB?

A

methyl orange

41
Q

What indicator for WAWB?

A

neither, must use a pH probe instead as no clear vertical part of the graph

42
Q

What is a buffer solution?

A

a solution that can resist changes in pH, an addition of small amounts of acid/alkali/water upon dilution

43
Q

Acidic buffers have a pH of…

A

less than 7

44
Q

What are acidic buffers?

A

a mixture of weak acid and it’s salt, ie. ethanoic acid and sodium ethanoate

45
Q

How do you make an acidic buffer?

A

-mix ethanoic acid and sodium ethanoate
or
-mix excess ethanoic acid and NaOH (cheaper)

46
Q

Name 3 uses of buffers?

A

-making dyes
-intravenous injections
-shampoo

47
Q

How do acidic buffers work?

A

-add a little HCl, the salt will react with the H+ (H+ + A- –> HA)
-overall [H+] and pH will remain approximately constant
-add a little -OH, the acid will react with the -OH (HA + -OH –> A- + H20)
-overall the [H+] and pH will remain approximately constant

48
Q

What happens if you add a little water?

A

moles of HA and A- remain constant, adding water does not change the moles of HA and A-, so [HA]/[A-] stays the same, so [H+] and pH remain approximately constant

49
Q

How do alkaline buffers work?

A

-add a little HCl, the salt will react with the base (H+ + B –> BA)
-overall [H+] and pH will remain approximately constant
-add a little -OH, the salt will react with the -OH (BH + -OH –> B + H20)
-overall the [H+] and pH will remain approximately constant

50
Q

Test for ammonium ions?

A

-warm sample with NaOH solution
-NH3 gas produced turns damp red litmus paper blue

physical chemistry (27 decks)

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