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AQA - A Level - Physical Chemistry > Brush Up > Flashcards

Flashcards in Brush Up Deck (61)
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1

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.)

2

An Acidic Buffer is a mixture of?

weak acid, HA & one of its salts, A⁻

3

Two ways of making Acidic buffers?

|>Add together weak acid & one of its salts

|>Partially neutralise some weak acid by adding a base

4

When OH⁻ is added to a basic buffer, what occurs?

|>OH⁻ reacts with BH⁺
|>Equilibrium shifts left
|>pH changes are minimised

5

When acid is added to a basic buffer, what occurs?

|>H⁺ reacts with OH⁻
|>Equilibrium shifts right
|>pH changes are minimised

6

A Basic buffer is a mixture of?

weak base, B & one of its salts, BH⁺

7

Equation for [H⁺] of a buffer?

[H⁺] = Ka x ([HA]/[A⁻])

8

When OH⁻ is added to a acidic buffer, what occurs?

|>OH⁻ reacts with H⁺
|>Equilibrium shifts right
|>pH changes are minimised

9

Two ways of making Basic buffers?

|>Add together weak base & one of its salts

|>Partially neutralise some weak base by adding an acid

10

When acid is added to a basic buffer, what occurs?

|>H⁺ reacts with A⁻
|>Equilibrium shifts left
|>pH changes are minimised

11

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

12

Define: Kw, ionic product of water

Kw = [H⁺][OH⁻]

13

When mixing strong acid & strong alkali
where Base is in excess, [H⁺] = ?

[H⁺] = Kw / (n(OH⁻)/total v.)

14

For weak acids, [H⁺] = ?

√Ka[HA]

assuming: [HA](equilibrium) = [HA](initial)
[H⁺] = [A⁻]

15

When mixing strong acid & strong alkali
where Acid is in excess, [H⁺] = ?

[H⁺] = n(H⁺)/total v.

16

the Most Reactive Metals have the
____ Eᶿ values?

Most Negative

17

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

18

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

19

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

20

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

21

the Most Reactive Non-metals have the
____ Eᶿ values?

Most Positive

22

Define: Standard Electrode Potential

e.m.f of a half cell compared with a standard hydrogen half-cell
Measured under standard conditions

23

Reduction occurs at the ____ electrode?

Positive

24

Equation for: mole fraction of a gas

Mole fraction = moles of gas in mixture/
of a gas total n of all gases in mixture

25

Equation for: Partial Pressure of a gas

Partial Pressure = mole fraction of gas x Total Pressure
of a gas

26

Equation for Gibbs free Energy Change, ΔG?

ΔG = ΔH - TΔS

27

Charge density increases if:

Charge Increases & Size Decreases

Charge Increases & Size is Constant

28

Charge density decreases if:

Charge Decreases & Size Increases

Charge is Constant & Size Increases

29

As Charge Density Increases, ΔhydH ____?

becomes less Exothermic

30

Define: Enthalpy of Lattice Formation ΔLFHᶿ

Enthalpy Change when
One mole of Ionic Substance
is formed from its Gaseous Ions