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8. Acids and Bases > Strong and weak acids and bases > Flashcards

Strong and weak acids and bases Flashcards

1
Q

What does the strength of an acid depend on?

A
  • The degree of dissociation (ionisation) in aqueous solution
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2
Q

What does dissociate and ionize mean?

A
  • Break apart an ionic compound into its constituent ions
  • Ionize means to from ions and is mainly used for covalent compounds
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3
Q

Explain the degree of dissociation for strong and weak acids.

A
  • Strong acids completely dissociate in solutions
  • Weak acids only partially dissociate in solution
  • Differ by extent of ionization
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4
Q

Explain strong acids. What is the general equation for dissociation of strong acids?

A
  • When a strong acid dissolves in water, it completely dissociates into ions H+ and OH-
  • HA = strong acid
  • HA (g or l) –> H+ (aq) + A- (aq)
  • A strong acid will contain no undissociated HA molecules
  • A strong acid the concentration of H+ is equal to the initial concentration of the acid
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5
Q

Explain weak acids. What is the general equation for dissociation of weak acids?

A
  • Small % of the acids molecules dissociate to from H3O+ ions
  • An equilibrium is reached, the majority of acid molecules do not dissociate into ions
  • Position of equilibrium on the left, Kc is small
  • HA (aq) ⇌ H+ (aq) + A- (aq)
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6
Q

Explain strong bases. What is the general equation for dissociation of strong base?

A
  • Completely dissociates into ions in aqueous solution. MOH is strong base
  • MOH (aq) –> M+ (aq) + OH- (aq)
  • The equilibrium position for the dissociation of a strong base lies to the right
  • For a strong base, the concentration of OH- ions is equal to the initial concen. of base
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7
Q

Explain weak bases. What is the general equation for dissociation of weak base?

A
  • Weak bases are made up of molecules that react with water to release hydroxide ions
  • ‘B’ is the weak base
  • B (aq) + H2O ⇌ BH+ (aq) + OH- (aq)
  • Position of equilibrium lies to the left and Kc is small
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8
Q

What is the OH- and H+ concentration of weak acids/bases compared to strong acids/bases?

A
  • Weak acids/bases, the equilibrium concentrations are much lower than for strong ones
  • The difference in concentration is used to distinguish between solutions of weak and strong acids/bases
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9
Q

What are equimolar solutions?

A
  • Solutions that have equal concentrations
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10
Q

What are three methods to distinguish between weak and strong acids/bases?

A
  • Must be same concentration, distinguished by pH, electrical conductivity, reactions with active metals
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11
Q

How does the pH scale distinguish between weak and strong acids?

A
  • Weak partially ionise in solution, different pH values
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12
Q

How does electrical conductivity distinguish between weak and strong acids?

A
  • Weak have lower concentration of mobile ions, poor conductors of electricity
  • Strong, completely ionize, more mobile ions, good conductors
  • Solutions must be of equal concentration
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13
Q

How do reactions with active metal distinguish between weak and strong acids?

A
  • E.g. zinc or magnesium, active (above H in activity series)
  • Can only distinguish between strong and weak acids, bases do not react with metals
  • Reaction with strong acid, reaction faster, more vigorous
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14
Q

How do metal oxides distinguish between weak and strong acids?

A
  • Metal oxides and metal carbonates, a faster reaction will be observed with a strong acid
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15
Q

How strong is the conjugate base in a reaction with a strong acid?

A
  • The water molecule acts as a stronger base than the chloride ion
  • Water has a greater tendency to accept a proton than the chloride ion
  • Acid will ionise more
  • Position of equilibrium lies to the right
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16
Q

How strong is the conjugate base in a reaction with a weak acid?

A
  • Ethanoate ion is a stronger base than the water molecule
  • Ethanoate ion has a greater tendency to accept a proton than water
  • Acid will partly dissociate
  • Position of equilibrium lies on the left
17
Q

Explain the relationship between acids and their conjugate bases.

A
  • Strong acids have weak conjugate bases, hence water acts as a stronger base
  • Weak acids have a strong conjugate base, hence the other base acts as a weaker base

8. Acids and Bases (5 decks)

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