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chemistry a level > Acids And Bases > Flashcards

Acids And Bases Flashcards

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1
Q

Bronsted – Lowry acid

A

Bronsted – Lowry acid proton donor

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2
Q

Bronsted – Lowry base

A

Bronsted – Lowry base proton acceptor

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3
Q

pH

A

Measure of acidity by measuring concentration of H+ ions

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4
Q

Low pH means

A

Acidity

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5
Q

High pH means

A

Alkalinity

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6
Q

Calculating pH equation

A

pH = -log[H+]

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7
Q

Calculating [H+]

A

-pH

[H+] = 10

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8
Q

What does an acid/base reaction involves

A

Transfer of the H+ ions from the acid to the base

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9
Q

Strong acid ful..

A

Strong acid fully dissociates in water

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10
Q

Weak acid

A

Only very Slightly dissociates in water

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11
Q

Ka weak acid dissociation constant

A

Ka= [H+] [A-]

[HA]

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12
Q

The more a weak acid dissociates…

A

The more H+ ions are formed

the stronger the acid the larger the Ka volume

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13
Q

Calculating pKa

A

pKa = -log (ka)

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14
Q

Calculating Ka from pKa

A

-pKa

Ka=10

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15
Q

Dissociation of water

A

H2O (reverse sign) H+/H3O+OH-

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16
Q

When water boils what happens to its pH

A

Water dissociating is endothermic and the reverse reaction is exothermic
Le chatliers principal
equilibrium shifts to rights to lower temperature more H+ ions So pH lower

17
Q

Oxonium ion

A

H3O+

18
Q

The ionic product of water at 298 Kelvin

A

Kw = [H+][OH-] = 1.0 x 10^-14

19
Q

Calculating pH of a base

A

[H⁺] = Kw

[OH⁻]

20
Q

Buffer

A

Buffer

Solution that maintains an almost constant pH on addition of small amounts of strong acid or strong base.

21
Q 
What does an acidic buffer consist of?
Weak acid (HA) with its salt (Na⁺A⁻)
A 
What does an acidic buffer consist of?
Weak acid (HA) with its salt (Na⁺A⁻)
22
Q

What does a basic buffer consist of

A

What does a basic buffer consist of?

Weak base with its salt.

23
Q

How can an acidic buffer be made?

A

How can an acidic buffer be made?
Mix HA with Na⁺A⁻.
Part-neutralise HA with NaOH.

24
Q

How can a basic buffer be made?

A

How can a basic buffer be made?
Mix weak base with its salt (e.g. NH₃ with NH₄Cl).
Part-neutralise weak base with HCl.

25
Q

When H⁺ added to acidic buffer…

A 
When H⁺ added to acidic buffer...
Unbalances equilibrium.
Higher concentration of H⁺.
Le Chatelier's principle.
H⁺ + A⁻ → HA
26
Q

When OH⁻ added to acidic buffer…

A 
OH⁻ + H⁺ → H₂O
Unbalances equilibrium.
Lower concentration of H⁺.
Le Chatelier's principle.
HA → H⁺ + A⁻
27
Q

When H⁺ added to basic buffer…

A 
OH⁻ + H⁺ → H₂O
Unbalances equilibrium.
Higher concentration of H₂O.
Le Chatelier's principle.
NH₃ + H₂O → NH₄⁺ + OH⁻
28
Q

When OH⁻ added to basic buffer…

A

Unbalances equilibrium.
Higher concentration of OH⁻.
Le Chatelier’s principle.
NH₄⁺ + OH⁻ → NH₃ + H₂O1.

29
Q

How is a pH titration carried out?

A

How is a pH titration carried out?

  1. Calibration curve of pH meter and electrode using buffer solutions.
  2. Prepare graph of pH (y-axis) against volume of alkali added (x-axis).
  3. Pipette 25cm³ 0.1M acid into 250cm³ beaker. Measure pH and record as initial pH.
  4. Add 0.1M alkali from burette in appropriate portions, measuring and plotting pH after each addition.
  5. Repeat up to 50cm³.
  6. Plot curve of best fit.
30
Q

Equivalence volume/endpoint

A

Equivalence volume/endpoint

Mi-point of “vertical section”.

31
Q

At half equivalence…

A

At half equivalence…
[A⁻] = [HA]
Ka = [H⁺]
pKa = pH

32
Q

Buffer region

A

Buffer region

Around pa where pH changes very little, despite acid/base being constantly added.

33
Q

Acid-base indicators

Weak acids.

A

Acid-base indicators
Weak acids.
Conjugate acid and base forms have different colours

34
Q

An indicator colour change must…

A

An indicator colour change must…
Be rapid
Occur at exactly the same time as the equivalence point.

35
Q

What colour changes does methyl orange show?

A

What colour changes does methyl orange show?
Yellow - pH5
Orange - pH4
Red - pH3

36
Q

What colour changes does phenolphthalein show?

A

What colour changes does phenolphthalein show?
Pink - pH10
Pale pink - pH9
Colourless - pH8

37
Q

When can you NOT use phenolphthalein?

A

When can you NOT use phenolphthalein?

With a weak base.

38
Q

When can you NOT use methyl orange?

A

When can you NOT use methyl orange?

With a weak acid.

chemistry a level (12 decks)

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