Module 5

Question 1

What is Kc?

Answer 1

A quantitative measure of the proportion of reactant in an equilibrium mixture. Large Kc means the equilibrium lies to the right with a high yield of products

Question 2

What is a homogenous equilibrium?

Answer 2

Contains species that all have the same state

Question 3

What is a heterogenous equilibrium?

Answer 3

Contains species that have different states

Question 4

What is Kp?

Answer 4

A equilibrium constant for gaseous equilibriums as it is more convenient to use partial pressures

Question 5

What is Lattice Enthalpy?

Answer 5

The enthalpy change when one mole of an ionic compound is formed from its gaseous ions

Question 6

Is bond forming endothermic or exothermic?

Answer 6

Exothermic

Question 7

2 factors that affect lattice enthalpy?

Answer 7

Ionic size (radius) - smaller ions attract more strongly than larger ions
Ionic charge - ions of greater charge attract more strongly than ions with a smaller charge

Question 8

What is standard enthalpy change of formation?

Answer 8

The enthalpy change when one mole of compound is formed from its elements in their standard states under standard conditions

Question 9

What is standard enthalpy of atomisation?

Answer 9

The enthalpy change when one mole of GASEOUS atoms is formed from its element in its standard state under standard conditions

Question 10

What is first ionisation energy?

Answer 10

The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 11

What is second ionisation energy

Answer 11

The enthalpy change when one electron is removed from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 12

What is first electron affinity?

Answer 12

The enthalpy change when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 13

When is second electron affinity

Answer 13

The enthalpy change when one electron is added to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions

Question 14

What is enthalpy change of solution?

Answer 14

The enthalpy change that takes place when one mole of a compound (solute) is completely dissolved in water under standard conditions

Question 15

What two processes take place when an ionic compound dissolves into water?

Answer 15

1) The ionic lattice dissociates into its gaseous ions (endothermic)
2) The gaseous ions are hydrated with H2O molecules (exothermic, +ve ions attract slightly negative O, -ve ions attract slightly positive H)

Question 16

What is standard enthalpy change of hydration?

Answer 16

The enthalpy that takes place when one mole of isolated gaseous ions is dissolved into water forming one mole of aqueous ions under standard conditions

Question 17

What are the standard conditions?

Answer 17

101kPa and 298K

Question 18

273K is what in degrees

Answer 18

1

Question 19

How to work out how many electrons are removed from a mass of an element

Answer 19

Take the grams of the element (mass)
divide the mass by the Mr
Times the answer to the above by Avogadro’s constant (in formula book)

Question 20

Name and bond angle:
2 bond pairs
0 lone pairs

Answer 20

Linear, 180

Question 21

Name and bond angle:
2 bond pairs
1 lone pair

Answer 21

Non-linear, 117.5

Question 22

Name and bond angle:
2 bond pairs
2 lone pairs

Answer 22

Non-linear, 104.5

Question 23

Name and bond angle:
3 bond pairs
0 lone pairs

Answer 23

Trigonal Planar, 120

Question 24

Name and bond angle:
3 bond pairs
1 lone pair

Answer 24

Pyramidal, 107

Question 25

Name and bond angle: 4 bond pairs 0 lone pairs

Answer 25

Tetrahedral, 109.5

Question 26

Name and bond angle: 6 bond pairs 0 lone pairs

Answer 26

Octahedral, 90

Question 27

What is entropy?

Answer 27

A measure of the dispersal of energy in a system. The entropy is greater when the system is more disordered. It is always positive. It increases with temperature

Question 28

What is standard entropy change of reaction?

Answer 28

The entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactant and products being in their standard states

Question 29

What sign does Gibbs (free energy change) need to be for a reaction to be feasible?

Answer 29

Negative

Question 30

Limitations of predictions made for feasibility

Answer 30

-Some reactions have a negative Gibbs but still do not seem to actually take place at the expected temperature -Feasibility predictions do not take into account the reactions kinetics (rate of reaction)

Question 31

What is the difference between NH3 and PH3?

Answer 31

NH3 has hydrogen bonding which is a stronger intermolecular force than PH3 has

Question 32

NaSO4 or Na2SO4?

Answer 32

Na2SO4

Question 33

How to work out enthalpy of formation?

Answer 33

Products-Reactants

Question 34

How to work out k from half lives

Answer 34

ln2/half life average

Question 35

If there are two weak acids, which acid becomes the acid in the acid-base pair

Answer 35

The acid with the higher Ka value

Question 36

Ka=

Answer 36

Ka=[H+]^2/[HA]

Question 37

pH of a buffer

Answer 37

pKa + log([A-]/[HA])

Question 38

Kw=

Answer 38

[H+][OH-] at 298K

Question 39

If you have pH how can you find the [OH-]?

Answer 39

14-pH = p0H 10^-pOH = [OH-]

Question 40

Acid is?

Answer 40

Acid is a proton donor

Question 41

Base is?

Answer 41

Base is a proton acceptor

Question 42

How is a choice of indicator linked to the pH curve?

Answer 42

Must change colour within the equivalence point

Question 43

What is a buffer solution?

Answer 43

A mixture that minimises pH change on addition of small amounts of an acid or base

Question 44

If the oxidation number is odd, eg (III) or (VII), how many oxygen in the compound and what is the charge

Answer 44

Oxygen = oxidation number + 1 / 2 Charge = -1

Question 45

If the oxidation number is even, eg (IV) or (VI), how many oxygen in the compound and what is the charge

Answer 45

Oxygen= oxidation number + 2 / 2 Charge = -2

Question 46

Is the oxidising agent in the flask or burette in a redox titration?

Answer 46

Burette

Question 47

What is the colour change of oxidation in a manganate (VII) redox titration?

Answer 47

pink to colourless

Question 48

What colour does starch indicator turn in the presence of iodine?

Answer 48

Blue-black

Question 49

Aqueous iodine is this colour

Answer 49

Brown

Question 50

Colour change at end point of titration of iodine and thiosulfate? (starch indicator added)

Answer 50

Blue-black to colourless

Question 51

Are the moles of titrated I2 the same as the "liberated"/redox product I2?

Answer 51

Yes :)

Question 52

More positive standard electrode potential means

Answer 52

greater tendency to gain electrons, and undergo reduction

Question 53

Standard conditions of electrochemical cells

Answer 53

298K 1.00moldm-3 1 atm

Question 54

If only aqueous/liquid in the half cell equation, what solid can be the electrode

Answer 54

Pt(s) / Platinum solid

Question 55

If there is a gas in the half cell equation what is needed?

Answer 55

A gas cylinder is placed over the electrode and low enough to be submerged in the solution. The gas is pumped into the solution this way

Question 56

What is between half cells

Answer 56

A salt bridge which completes the electrical circuit and allows the movement of ions between the two half cells

Question 57

Standard hydrogen half cell

Answer 57

2H+(aq) + 2e- (reversable arrow) H2(g) -needs H2(g) (at 1 atm) pumping into H+(aq) (at 1.00moldm-3) -needs a solid platinum electrode

Question 58

What is the standard electrode potential of a half cell?

Answer 58

The electromotive force/voltage of a half cell compared with a standard hydrogen half-cell, measured at 298K with solution concentrations of 1moldm-3 and a gas pressure of 1atm

Question 59

Is the standard cell potential positive or negative?

Answer 59

Positive

Question 60

What are primary cells?

Answer 60

Non-rechargeable (provide electrical energy until the chemicals have reacted to such an extent that the voltage falls and the cell is 'flat'

Question 61

What are secondary cells?

Answer 61

Rechargeable The reaction that provides electrical energy can be reversed during the recharging process

Question 62

What is a fuel cell?

Answer 62

A fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage

Question 63

Alkali Hydrogen-Oxygen fuel cell

Answer 63

Reduction: 1/2O2(g) + H2O(l) +2e- -> 2OH- Oxidation: H2(g) + 2OH-(aq) -> 2H2O(l) + 2e- Redox: H2(g) + 1/2O2(g) -> H2O(l)

Question 64

Acid Hydrogen-Oxygen fuel cell

Answer 64

Reduction: 1/2O2(g) + 2H+(aq) + 2e- -> H20(l) Oxidation: H2(g) -> 2H+(aq) + 2e- Redox: H2(g) + 1/2O2(g) -> H2O(l)

Question 65

On a concentration-rate graph, which order corresponds to which line: -Straight across -Straight diagonal increasing -Increasing curve

Answer 65

-Straight across is order 0 -Straight diagonal increasing is 1st order -Increasing curve is 2nd order

Question 66

On a concentration-time graph, which order corresponds to which: -Straight diagonal decreasing -Decreasing curve with constant half lives -Decreasing curve with non constant half lives

Answer 66

Straight diagonal decreasing is order 0 Decreasing curve with constant half lives is 1st order Decreasing curve with non constant half lives is 2nd order

Question 67

What is the rate determining step?

Answer 67

The slowest step in a multistep reaction

Question 68

Does a catalyst effect Kc and Kp?

Answer 68

No. It increases the rate of both the forward and reverse reactions by the same amount.

Question 69

Does pressure affect Kp?

Answer 69

No

Question 70

If the forward reaction is exothermic and temperature increases, what is the effect on Kp/c

Answer 70

The value decreases

Question 71

If the forward reaction is endothermic and temperature increases, what is the effect on Kp/c

Answer 71

The value increases

Question 72

Does concentration effect Kc?

Answer 72

No

Question 73

What colour is Mn0₄¯?

Answer 73

Purple

Question 74

What colour is Cr₂O₇²¯?

Answer 74

Orange

Question 75

What colour is Cu²+?

Answer 75

Blue

Question 76

What colour is Cu(OH)₂ and what state symbol should it have?

Answer 76

Blue(s) Precipitate

Question 77

What colour is Fe²+?

Answer 77

Pale Green

Question 78

What colour is Fe(OH)₂ and what state symbol should it have?

Answer 78

Green(s) Precipitate

Question 79

What colour is Fe³+?

Answer 79

Yellow

Question 80

What colour is Fe(OH)₃ and what state symbol should it have?

Answer 80

Rusty-Brown(s) Precipitate

Question 81

What colour is Mn²+?

Answer 81

Pale Pink

Question 82

What colour is Mn(OH)₂ and what state symbol should it have?

Answer 82

Light-Brown(s) Precipitate

Question 83

What colour is Cr³+?

Answer 83

Violet (or Green)

Question 84

What colour is Cr(OH)₃ and what state symbol should it have?

Answer 84

Grey-Green(s) Precipitate

Question 85

How is a OH¯ ion produced for a precipitation reaction?

Answer 85

Either from aqueous sodium hydroxide, or aqueous ammonia (whereby the ammonia reacts with water to make an equilibrium with OH¯ and NH₄+

Question 86

What do you make from reacting a large excess of NH₃(aq) and Cu²+?

Answer 86

Blue precipitate made first will dissolve to a deep blue solution. The complex ion formed contains 4NH₃ ligands and 2H₂O ligands

Question 87

What do you make from reacting Cu²+ and large excess of concentrated HCl(aq)?

Answer 87

Blue solution will turn yellow. If HCl is added dropwise until excess a green solution will appear before the yellow. The complex ion formed has 4Cl¯ ligands and a 2¯ charge

Question 88

What happens when a large excess of NaOH(aq) is reacted with Cr³+?

Answer 88

The grey-green precipitate will dissolve to make a green solution. The complex ion formed has 6OH¯ ligands and a charge of 3¯

Question 89

What happens when an excess of NH₃(aq) reacts with Cr³+?

Answer 89

A purple solution is formed and the grey-green precipitate will dissolve. The complex ion formed had 6NH₃ ligands. 6 molecules of water are a biproduct of this reaction.

Question 90

What three transition element ions don’t change colour when excess NaOH or excess NH₃ is added?

Answer 90

Fe²+, Fe³+ and Mn²+