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Flashcards in Brush Up Deck (61)
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1
Q

How do you calculate pH of a buffer solution by mixing an acid and a base?

A

|>Calculate initial n
|>smallest reactant n is used up
|>[H⁺] = Ka x ([HA]/[A⁻])
|>[H⁺] = Kw / (n(OH⁻)/total v.)

2
Q

An Acidic Buffer is a mixture of?

A

weak acid, HA & one of its salts, A⁻

3
Q

Two ways of making Acidic buffers?

A

|>Add together weak acid & one of its salts

|>Partially neutralise some weak acid by adding a base

4
Q

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

A

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

5
Q

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

A

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

6
Q

A Basic buffer is a mixture of?

A

weak base, B & one of its salts, BH⁺

7
Q

Equation for [H⁺] of a buffer?

A

[H⁺] = Ka x ([HA]/[A⁻])

8
Q

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

A

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

9
Q

Two ways of making Basic buffers?

A

|>Add together weak base & one of its salts

|>Partially neutralise some weak base by adding an acid

10
Q

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

A

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

11
Q

Method to make a buffer?

A
|>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
Q

Define: Kw, ionic product of water

A

Kw = [H⁺][OH⁻]

13
Q

When mixing strong acid & strong alkali

where Base is in excess, [H⁺] = ?

A

[H⁺] = Kw / (n(OH⁻)/total v.)

14
Q

For weak acids, [H⁺] = ?

A

√Ka[HA]

assuming: HA = HA
[H⁺] = [A⁻]

15
Q

When mixing strong acid & strong alkali

where Acid is in excess, [H⁺] = ?

A

[H⁺] = n(H⁺)/total v.

16
Q

the Most Reactive Metals have the

____ Eᶿ values?

A

Most Negative

17
Q

if Concentration of Ions in the Left Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____

A

Shifts Right
Less Negative
Decreases
Cell has smaller difference in E

18
Q

if Concentration of Ions in the Right Half-Cell
Decreases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____

A

Shifts Left
Less Positive
Decreases
Cell has smaller difference in E

19
Q

if Concentration of Ions in the Right Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____

A

Shifts Right
More Positive
Increases
Cell has bigger difference in E

20
Q

if Concentration of Ions in the Right Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____

A

Shifts Left
More Negative
Increases
Cell has bigger difference in E

21
Q

the Most Reactive Non-metals have the

____ Eᶿ values?

A

Most Positive

22
Q

Define: Standard Electrode Potential

A

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

23
Q

Reduction occurs at the ____ electrode?

A

Positive

24
Q

Equation for: mole fraction of a gas

A

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

25
Q

Equation for: Partial Pressure of a gas

A

Partial Pressure = mole fraction of gas x Total Pressure

of a gas

26
Q

Equation for Gibbs free Energy Change, ΔG?

A

ΔG = ΔH - TΔS

27
Q

Charge density increases if:

A

Charge Increases & Size Decreases

Charge Increases & Size is Constant

28
Q

Charge density decreases if:

A

Charge Decreases & Size Increases

Charge is Constant & Size Increases

29
Q

As Charge Density Increases, ΔhydH ____?

A

becomes less Exothermic

30
Q

Define: Enthalpy of Lattice Formation ΔLFHᶿ

A

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

31
Q

Forming bonds is ____ ?

A

Exothermic

Energy is Given out

32
Q

As Charge Density Increases, ΔLDH ____?

A

becomes less Exothermic

33
Q

Lattice Dissociation Enthalpies are ____ because bonds ____?

A

Endothermic

Bonds are being Broken

34
Q

As Charge Density Decreases, ΔLDH ____?

A

becomes more Exothermic

35
Q

As Charge Density Decreases, ΔLFH ____?

A

becomes less Exothermic

36
Q

As Charge Density Increases, ΔLFH ____?

A

becomes more Exothermic

37
Q

Why are ionic compounds w/ Exothermic
Enthalpy Changes of Solution
more likely to Dissolve?

A

More energy is Released when Ions are Hydrated than is needed in
Dissociation

38
Q

Define: Enthalpy of Hydration ΔhydHᶿ

A

Enthalpy Change when
One mole of Aqueous Ions is formed from
One mole of Gaseous Ions

39
Q

For Born-Haber cycles, Endothermic reactions are represented by ____?

A

Arrows pointing up

40
Q

As Charge Density Increases, ΔhydH ____?

A

becomes less Exothermic

41
Q

As Charge Density Decreases, ΔhydH ____?

A

becomes more Exothermic

42
Q

Why is a Compromise temp of 450°C used?

A

High for Fast Rate

Low for Increased Yield

43
Q

As a reaction occurs, the rate ____ as conc. of reactant ____?

A

Decreases

Falls

44
Q

Why is using Mean Bond Enthalpies less accurate than Hess’ Law?

A

Mean average is used

Assumption all reactions are gaseous

45
Q

Two examples of Endothermic reactions?

A

Thermal decomposition of CaCO₃

Photosynthesis

46
Q

Equation to calculate ΔH in KJmol⁻¹

A

ΔH = q(x10⁻³ if q in J) / mol

47
Q

What is Calorimetry?

A

Method to determine Enthalpy changes by experiment, converting temp. change of water to quantity of heat energy

48
Q

Define: Bond Enthalpy

A

Energy Required to break

One mole of a given Covalent bond in gaseous molecules

49
Q

Define: Enthalpy

A

Heat energy stored in a chemical system

50
Q

How much does Hydrogen Bonding increase water’s b.p.t by?

A

about 200°C

51
Q

Charge of Sulfate(IV) ion?

A

SO₃²⁻

52
Q

Charge of Nitrate(III) ion?

A

NO₂⁻

53
Q

Charge of Nitrate(V) ion?

A

NO₃⁻

54
Q

Charge of Sulfate(VI) ion?

A

SO₄²⁻

55
Q

Shape and Bond Angle: Water?

A

Trigonal Pyramidal

107°

56
Q

Steps to find conc. of a solution of a base?

A

|>Fill a burette w/ standard solution of acid
|>Pipette known volume of base into conical flask
|>Add a few drops of indicator
|>Add solution until indicator changes colour
|>Record volume to the nearest 0.05cm³
|>Perform rough titration, then accurate ones to calculate mean from concordant values

57
Q

Steps for making a standard solution?

A

|>Dissolve a known mass of solid in Deionised Water
|>Using a funnel, transfer into a volumetric flask, including washings
|>Make up to a certain volume
|>Invert to mix contents

58
Q

Stages of Electron Bombardment Ionisation

A

|>Vapourise
|>Fire high energy Electrons at sample using electron gun
|>knocks off electron

59
Q

Stages of Electrospray Ionisation?

A

|>Dissolve sample in volatile solvent
|>Pass through a fine needle to create mist
|>Apply high voltage to tip of needle
|>Sample gains H⁺

60
Q

How to calculate no. of moles of water of crystallisation?

A

|>Need to know mass of hydrated & anhydrous salts
|>Mass of water = mass hydrated - mass anhydrous
|>Work out no. of moles of anhydrous salt
& of water
|>Find simplest ratio

61
Q

Equation for Ar?

A

Σ(mass x abundance of each isotope)/

total abundance