Brush Up Flashcards
How do you calculate pH of a buffer solution by mixing an acid and a base?
|>Calculate initial n
|>smallest reactant n is used up
|>[H⁺] = Ka x ([HA]/[A⁻])
|>[H⁺] = Kw / (n(OH⁻)/total v.)
An Acidic Buffer is a mixture of?
weak acid, HA & one of its salts, A⁻
Two ways of making Acidic buffers?
|>Add together weak acid & one of its salts
|>Partially neutralise some weak acid by adding a base
When OH⁻ is added to a basic buffer, what occurs?
|>OH⁻ reacts with BH⁺
|>Equilibrium shifts left
|>pH changes are minimised
When acid is added to a basic buffer, what occurs?
|>H⁺ reacts with OH⁻
|>Equilibrium shifts right
|>pH changes are minimised
A Basic buffer is a mixture of?
weak base, B & one of its salts, BH⁺
Equation for [H⁺] of a buffer?
[H⁺] = Ka x ([HA]/[A⁻])
When OH⁻ is added to a acidic buffer, what occurs?
|>OH⁻ reacts with H⁺
|>Equilibrium shifts right
|>pH changes are minimised
Two ways of making Basic buffers?
|>Add together weak base & one of its salts
|>Partially neutralise some weak base by adding an acid
When acid is added to a basic buffer, what occurs?
|>H⁺ reacts with A⁻
|>Equilibrium shifts left
|>pH changes are minimised
Method to make a buffer?
|>Weigh accurately Xg of salt (A⁻) |>In a beaker, dissolve in its acid (HA) |>Using a funnel, transfer to volumetric flask |>Include washings |>Make up to mark with acid |>Invert multiple times to mix
Define: Kw, ionic product of water
Kw = [H⁺][OH⁻]
When mixing strong acid & strong alkali
where Base is in excess, [H⁺] = ?
[H⁺] = Kw / (n(OH⁻)/total v.)
When mixing strong acid & strong alkali
where Acid is in excess, [H⁺] = ?
[H⁺] = n(H⁺)/total v.
the Most Reactive Metals have the
____ Eᶿ values?
Most Negative
if Concentration of Ions in the Left Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Right
Less Negative
Decreases
Cell has smaller difference in E
if Concentration of Ions in the Right Half-Cell
Decreases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Left
Less Positive
Decreases
Cell has smaller difference in E
if Concentration of Ions in the Right Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Right
More Positive
Increases
Cell has bigger difference in E
if Concentration of Ions in the Right Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Left
More Negative
Increases
Cell has bigger difference in E
the Most Reactive Non-metals have the
____ Eᶿ values?
Most Positive
Define: Standard Electrode Potential
e.m.f of a half cell compared with a standard hydrogen half-cell
Measured under standard conditions
Reduction occurs at the ____ electrode?
Positive
Equation for: mole fraction of a gas
Mole fraction = moles of gas in mixture/
of a gas total n of all gases in mixture
