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A-levels > Chemistry- Acids, Bases and Alkalis > Flashcards

Chemistry- Acids, Bases and Alkalis Flashcards

1
Q

Define an Acid

A

A molecule or other species which can donate a proton or accept and electron pair in a reaction.

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2
Q

What is a strong and weak Acid?

A

Strong acid can dissociate protons (h+ ions) more than a weak acid.
Weak acids have more un-dissociated protons.

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3
Q

What is an Arrhenius acid?

A

A substance that produces hydrogen ions (H+) in solution.

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4
Q

What is a Bronsted-lowry acid?

A

A substance that is a proton donor

A base is a proton acceptor.

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5
Q

What is the difference between strength and concentration?

A

Strength is how much an acid dissociates H+ ions in solution.

Concentration is the ratio of how much acid present in the solution both dissociated and associated.

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6
Q

What is produced when an acid and alkali react together?

A

Salt + water

Acid + Alkali —-> Salt + Water

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7
Q

What happens when an acid and base react together?

A

Salt + Water

Acid + Base —-> Salt + Water

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8
Q

What is formed when an acid and metal carbonate react together?

A

Salt + Water + Carbon dioxide
Acid + Metal carbonate —-> Salt + Water + Carbon
Dioxide

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9
Q

What happens when a metal and acid react together?

A

Salt + Hydrogen

Metal + Acid —-> Salt + Hydrogen

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10
Q

Write the dissociation equation for Nitric Acid (HNO3)

A

HNO3 —-> H+ + NO3-

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11
Q

Write the full ionic equation for the acid-base reaction between sulphuric acid and solid magnesium carbonate?

A 
Full Equation:
H2SO4 + MgCO3 ---> MgSO4 + H2O + CO2
Ions:
2H^+ + SO4^2- + MgCO3 --->  Mg^2+ + SO4^2- + H2O + CO2
Ionic Equation:
2H^+ + MgCO3 ---> Mg^2+ + H2O + CO2
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12
Q

What are Mono, Di and Tri Basic acids?

A

Monobasic Acid= each molecule can release 1 proton
HCl —> H^+ + Cl^-
Dibasic Acid= Each molecule can release 2 protons
H2SO4 —> H^+ + HSO4^-
HSO4^- —> H^+ + SO4^2-
Tribasic Acid= Each molecule can release 3 protons
H3PO4 —> H^+ + H2PO4^-
H2PO4 —> H^+ + H2PO4^2-
HPO4^2- —> H^+ + PO4^3-

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13
Q

What is a conjugate acid-base pair?

A

A pair of 2 species that transform into each other by gain or loss of a proton.
e.g. HNO2 H^+ + NO^2-
Acid Base
H^+ links an acid with its conjugate base

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14
Q

Identify the acid, base conjugate acid and conjugate base for the reaction of
HClO4 + H2O H3O^+ + ClO4^-

A

HClO4 + H2O H30^+ + ClO4^-
Acid 1 base1 acid 2 base 2

Acid & base 2 = conjugate acid and base

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15
Q

What does pH measure?

A

Measures the amount of H+ present

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16
Q

What are the equations linking concentration of H+ ions and pH?

A 
pH = -log([H+])
[H+] = 10^-pH
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17
Q

Key points on the relationship between pH and [H+]

A
  • Low pH means larger [H+]
  • High pH means lower [H+]
  • A pH change of 1 changes [H+] by 10x
  • An acid with a pH of 2 contains 1000x [H+] of an acid with a pH of 5
18
Q

What is an amphoteric substance?

A

A substance that can act as an acid or a base.
e.g Water (H2O)
H2O Donate H+ —-> :OH^-
H2O accepts H+ —-> H3O^+

19
Q

Define a strong acid

A

An acid that can dissociate completely in aqueous solutions.

HA H+ + A-

20
Q

How is dissociation measured?

A

Extent of dissociation is measured by an equilibrium constant and dissociation constant (Ka)

21
Q

What does a large and small Ka value mean in terms of acidity?

A

Large Ka value = Strong Acid

Small Ka value = Weak Acid

22
Q

Since Ka numbers can be large what is done to make them easier to use in calculations?

A

Logarithmic Scale —> turned into pKa Values
pKa = -log(Ka)
Ka = 10^-pKa

Large pKa = Weak Acid
Small pKa = Strong Acid

23
Q

What is the equation when using Ka?

A

Ka = [H+][A-] / [HA]

larger number on top means a stronger acid

24
Q

What is the ionic product of water equation?

A

Kw = [H+][OH-]

Kw = 1.0x10^-14 mol^2dm^-6 @ 298K (always)

25
Q

What affects Ka Values?

A

Only Temperature:
As temperature increases more H2O dissociates so both [H+] and [OH-] increase.
Therefore the pH of neutrality decreases.

26
Q

Define Endpoint

A

The point at which the indicator changes colour.

27
Q

Define Equivalence point

A

The term for the moment when neutralisation occurs.

28
Q

What is an acid-base indicator?

A

An Acid-base indicator is a weak acid represented as HIn.
An indicator has one colour in its acid form (HIn) and a different colour in its conjugate base form (In-)
eg. Methyl Orange HIn - Red
In^- - Yellow

29
Q

What is the Value of Kw at 298K?

A

1x10^-14

30
Q

Define a weak acid

A

An acid that does not fully dissociate (ionise) when dissolved in water.

31
Q

Where does equilibrium for a weak acid and water tend to lie?

A

The position of equilibrium between the acid and water varies from one weak acid to the other.
The further left equilibrium lies, the weaker the acid.

32
Q

What is the acid dissociation constant for a weak acid and its equation?

A

Ka
Ka = [H+][OH-] / [HA]

Lower the value for the constant the more equilibrium lies to the left

33
Q

What do larger and smaller Ka Values mean?

A

Larger Ka = Stronger Acid

Smaller Ka = Weaker Acid

34
Q

Define pKa and what is its relationship to Ka similar to?

A

pKa = -log(Ka)
Ka = 10^-pKa
Similar relationship to pH and [H+]

35
Q

What doe larger and smaller pKa values mean?

A

Larger pKa = Weaker Acid

Smaller pKa = Stronger Acid

36
Q

How can we calculate pH of weak acids?

A 
Be given a Ka value and [HA]
ka = [H+][OH-] / [HA]
Ka = [H+]^2 / [HA]
[H+] = Square root ( Ka x [HA])
pH = -log[H+]
37
Q

What does a buffer do?

A

A buffer can resist changes to pH.

This is achieved by neutralising the H+ ions or OH- ions.

38
Q

How is a buffer made?

A

Made from a weak acid and its salt.
eg. Ethanoic acid and sodium ethanoate.
CH3COOH CH3COO-Na+

39
Q

What happens when an alkali is added to the buffer?

A

CH3COOH H+ + CH3COO-
- H+ ions would neutralise OH- ions from the alkali and therefore get used up.
- So equilibrium will shift to the right producing more H+ ions
Which means that the pH remains constant.

40
Q

What happens when an acid is added to the buffer?

A

CH3COOH H+ + CH3COO-
- Adding more H+ ions would increase the H+ ion concentration
- So equilibrium would shift to the left reducing the [H+] since a large number of ethanoate ions from reaction are added.
Therefore removing H+ and maintaining a constant pH.

A-levels (23 decks)

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