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A Level Chemistry > 3.1.12 Acids And Bases > Flashcards

3.1.12 Acids And Bases Flashcards

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1
Q

Conjugate acid

A

The species produced when a base gains a proton.

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2
Q

Conjugate base

A

The species produced when an acid loses a proton.

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3
Q

Conjugate acid-base pair

A

Two species related to one another by the presence of a hydrogen ion or its absence

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4
Q

pH =

A

-log10[H^+]

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5
Q

Kw=

A

[H^+][OH^-]
Delivered from equilibrium constant of water dissociation
Varies with temp

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6
Q

State the meaning of the term Brønsted–Lowry acid

A

Proton donor

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7
Q

Strong acid + strong base indicator

A

Methyl orange or phenolphthalein

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8
Q

Weak acid + strong base indicator

A

Phenolphthalein

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9
Q

Strong acid + weak base indicator

A

Methyl orange

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10
Q

Suggest why chloroethanoic acid is a stronger acid than ethanoic acid.

A

Cl more electronegative
Weakens O-H bond

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11
Q

State why calibrating a pH meter just before it is used improves the accuracy of the pH measurement

A

Over time/storage readings less accurate

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12
Q

Describe how you would obtain the pH curve for the titration

A

Measure pH of acid
Add alkali in 2cm^3 portions
Stir
Measure pH after every portion
When pH reaches end point, add acid in 0.2cm^3 portions
Repeat until alkali in excess
Continue with 2cm^3 portions post end point

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13
Q

Acid-base equilibria

A

Involves transfer of protons

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14
Q

Why is logarithmic scale used for pH

A

Concentration of H+ ions in aqueous solution covers very large range

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15
Q

Ka =

A

Dissociation constant of weak acid
[H^+][A^-]/[HA]

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16
Q

pKa =

A

-log [Ka]

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17
Q

Buffer solution

A

Maintains an approximately constant pH dispute dilution or addition of small amounts of acid or base

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18
Q

Acidic buffer contains

A

Weak acid and the salt of that weak acid

19
Q

Basic buffer solution contains

A

Weak base and the salt of that weak base

20
Q

State how a buffer solution can be made from solutions of potassium hydroxide and ethanoic acid
Give equation
How does buffer resist small additions of acid

A

Add enough KOH that the acid contains mixture of ethanoic acid and ethanoate ions
Add excess ethanoic acid to KOH and enough KOH so acid is partially neutralised
KOH + CH3COOH —> CH3COOK + H2O
CH3COO^- reacts with acid

21
Q

Define weak acid and weak base

A

Acid/base that doesn’t fully dissociate in solution

22
Q

Equivalence point

A

Point in titration at which the amount of titrant added is just enough to completely neutralize the analyte solution

23
Q

What happens at the half neutralisation point on curves

A

pH=pKa

24
Q

How do buffers work

A

Resist pH changes upon the addition of an acidic or basic components. It is able to neutralize small amounts of added acid or base to keep pH stable

25
Q

Lewis acid/base

A

Species that accepts/donates a pair of electrons

26
Q

Describe what happens in Brønsted−Lowry acid−base reaction

A

When a Brønsted-Lowry acid loses a proton, a conjugate base is formed. A Brønsted-Lowry base gains a proton, a conjugate acid is formed

27
Q

Explain why the end point of a reaction could be difficult to judge accurately using an indicator

A

Change in pH can be gradual
An indicator would change colour over a range of volumes

28
Q

What physical factors affect Kw + how

A

Temperature
If increased, equilibrium moves right
Kw increases + pH decreases

29
Q

Why is pure water still neutral when pH doesn’t equal 7

A

[H^+] = [OH^-]

30
Q

What is titration (acid/base)

A

The addition of an acid/base of known titration to a base/acid of unknown titration to determine the concentration
An indicator is used to show that neutralisation has occurred

31
Q

Titration curve for strong acid + weak base

A
32
Q

Titration curve for strong acid + weak base

A
33
Q

Titration curve for weak acid + weak base

A
34
Q

Titration curve for weak acid + strong base

A
35
Q

What happens to pH of solution around equivalence point

A

Large + rapid change in PH (except in weak acid/weak base titration)

36
Q

3 properties of a good indicator

A

Sharp colour change (one drop)
End point the same as equivalence point
Distinct colour change

37
Q

What colour is methyl orange in acid and alkali
What pH does is change

A

Acid-red
Alkali-yellow
pH-4.5

38
Q

What colour is methyl orange in acid and alkali
What pH does is change

A

Acid-colourless
Alkali-red
pH-9-10

39
Q

Equation for acidic buffer with added acid

A

A^- + H^+ —> HA

40
Q

Equation for acidic buffer with added alkali

A

HA + OH^- —> H2O + A^-

41
Q

How can you achieved an acidic buffer solution other than just mixing the constituents

A

Neutralise half of a weak acid with an alkali
Forms weak acid/soluble salt mixture

42
Q

Equation for buffer system which maintains blood pH at 7.4

A

H^+ + HCO3 ^- <=> CO2 + H2O

43
Q

What products are buffers found in

A

Shampoos, detergents

A Level Chemistry (36 decks)

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