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Chemistry > 5.1.3: Acids, bases and buffers > Flashcards

5.1.3: Acids, bases and buffers Flashcards

1
Q

Give Bronsted Lowry definition of an acid

A

Species which is a proton donor

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2
Q

Give Bronsted Lowry definition of a base

A

Species which is a proton acceptor

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3
Q

Explain monobasic acids and give an example

A
  • 1 mole of acid produces one mole of H+ ions and each molecule can release 1 proton
  • HCl
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4
Q

Explain dibasic acids and give an example

A
  • 1 mole of acid produces 2 moles of H+ ions and each molecule can release 2 protons
  • H2SO4
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5
Q

Explain tribasic acids and give an example

A
  • 1 mole of acid can produce 3 moles of H+ ions and each molecule can release 3 protons
  • H3PO4
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6
Q

Metal + acid =

A

Salt + hydrogen

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7
Q

Acid + base =

A

Salt + water

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8
Q

Acid + metal carbonate =

A

Carbon dioxide + water + salt

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9
Q

Acid + metal oxide =

A

Salt + water

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10
Q

Acid + alkali =

A

Salt + water

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11
Q

What ion is formed from acid dissociation which is simplified to H+ and give a feature of it

A

Hydronium ion
H3O+
Has a dative covalent bond

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12
Q

What is the acid dissociation constant ?

A

Ka

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13
Q

What type of acids are Ka used for ?

A

Weak acids

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14
Q

What does it mean if Ka is larger ?

A

Species is a stronger weak acid as more H+ dissociation has caused equillibrium to shift right

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15
Q

Ehat does it mean if pKa is lower ?

A

Species is a stronger weak acid as it means Ka will be larger

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16
Q

What are the 2 equations showing the relationship between Ka and pKa ?

A

pKa = -log(10) Ka
Ka = 10-pKa

17
Q

Define weak acids and give an example

A

Dissociates partially in an aqueas solution
- Carboxylic acids

18
Q

Define strong acids and give 3 examples

A

Dissociates fully in aqueas solutions
- HCl, H2SO4,H2SO4

19
Q

Define strong base and give 2 examples

A

Dissociates fully
- NaOH, KOH

20
Q

Define weak base and give an example

A

Dissociates partially
-NH3

21
Q

Give the equations to show the relationship between pH and H+

A

pH = -log[H+]
[H+] = 10-pH

22
Q

What does a low pKa mean in terms of pH?

A

Low pH

23
Q

What is the expression for the ionic product of water ?

A

Kw

24
Q

What is the standard value for Kw ?

A

At 25 degrees Kw = 1 x 10^14 mol^2dm-6

25
Q

How do you calculate Kw ? What happens with H20 ?

A

[H+][OH-]
Negligible dissocaition of water so assume concentration of water is constant

26
Q

Give the equation including Ka , [H+] and HA

A

[H+]2
Ka = ———————–
[HA]

27
Q

What approximation do we use for weak acid calculations ?

A

[HA]equillibrium = [HA]undissociated
[H+] = [A-]

28
Q

What is a limitation to using the approximation for ‘stronger’ weak acids?

A

Once the amount of dissociation is above 5%, Ka is far away from true value as weak acid increases strength

29
Q

Define buffer

A

A system that minimises pH changes on addition of small amount of acid or base

30
Q

Give the 2 ways a buffer can be formed

A

Weak acid + salt of weak acid
Excess weak acid and strong alkali

31
Q

What is the role of a conjugate acid-base pair in an acid buffer solution ?

A
  • When [H+] increases [H+] ions react with conjugate base to remove acid and cause equillibrium to shift to left
  • When [OH-] increases small concentrations of [H+] react with the [OH-] ions to restore [H+] and shift equillibrium to right
32
Q

Give the 3 steps to calculate the pH of a buffer and what 2 assumptions are made

A
  • Ka value
  • Conc. weak acid
  • Conc. salt

[HA]equillibrium = [HA]undissociated
[salt] = [A-]

33
Q

Name and explain a biochemically important buffer

A
  • Carbonic acid - hydrogencarbonate system
  • Controls blood pH to maintain it between 7.35 and 7.45
  • Present in blood plasma
  • Carbonic acid = weak acid
  • Hydrogen carbonate = conjugate base
34
Q

How is a suitable indicator selected ?

A

-Must have colour change which falls within rapid vertical pH change section of curve
- Colour change is around pKa of indicator

35
Q

What causes a colour change of an indicator ? What is the indicator considered as ?

A
  • Equillibrium shift between acid and conjugate base
  • [HA] weak acid
36
Q

For which type of titration is no indicator suitable for ?

A

Weak acid or weak base

Chemistry (38 decks)

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