Redox Equilibria

Question 1

What does this equation represent
M+n(aq) + ne- <==> M(s)

Answer 1

A dynamic equilibrium

Question 2

Define dynamic equilibrium

Answer 2

Rate at which
Ion leaving surface of metal to go into solution = it joining metal from solution

Question 3

3 ways to measure standard electrode potential

Answer 3

1.Measuring emf of metal
2. Emf of gas
3. EMF of ions

Question 4

Emf of ions checked in which 2 ways

Answer 4

1. Fe+2 and fe+3
2. Br and I

( ions of same element with different oxidation numbers)
( non metals and their ions in solution)

Question 5

Magnesium has greater negative charge
Than copper. Explain where equilibrium position of it will be

Answer 5

Mg release more electrons.
More +ve ions in sol
Equilibrium further to the left

Question 6

When writing equations where should electrons be

Answer 6

Electrons in the left hand side of equation

Question 7

Reason for reference electrode

Answer 7

You already know it’s potential so when u find potential of the metal u want u can subtract the known potential of reference electrode from the value u get

Question 8

Draw she diagrams do flashcard laptop

Answer 8

Jejs

Question 9

Importance of using standard conditions when measuring potential

Answer 9

Gas pressure 100kpa
Temp 298K
Conc of ions 1moldm-3

Question 10

Define standard electrode potential

Answer 10

Emf measured when a half-cell is connected to a standard hydrogen electrode under standard conditions of …..

Question 11

Why salt bridge needed

Answer 11

To complete the electrical circuit

Question 12

What does salt bridge usually contain

Answer 12

Conc sol of kNO3 (l) or gel

( any ionic salt)

Question 13

What does salt bridge do

Answer 13

Allows movement of ions

Question 14

Which type of ionic salts should be in salt bridge

Answer 14

Neither of the ions present should interfere with the components of the half-cell

Question 15

In a simple cell which is cathode and anode

Answer 15

More reactive metal act as anode

Question 16

Why high resistance voltmeter used

Answer 16

so that there is no flow of electrons

( so both halfcell reactiins are in equilibrium )

Question 18

Negative Ecell value does not mean equilibrium lies to the left so what does it mean

Answer 18

It means that it lies FURTHER to the left than equilibrium of SHE

Question 19

If metal has negative potential value what does it mean

Answer 19

Equilibrium = further to left
Electrons = released more readily
Oxidized = easily
Agent = better reducing than other …………….metal

Question 20

What does reducing agent do

Answer 20

Adds electrons to other species

So it loses electrons

So it’s oxidized

Question 21

For all electrochemical and electrolytic cells which is anode and cathode

Answer 21

Anode = electrode where oxi takeplace
Cath = red takes place

Question 22

EMF

Answer 22

Measured potential difference of a cell when no current is flowing

Question 23

Reactivity series

Answer 23

KNaCaMgAlZnFeTHCuAgAu

Question 24

How charge flows in electrochemical cell

Answer 24

E- move through Pt from anode to cath
Ions flow through salt bridge

Question 25

Define absolute potential difference

Answer 25

The potential difference between a metal and a solution of its ions

Question 26

If thermodynamicall reaction not feasible

Answer 26

Electrons not released No reaction takes place

Question 27

If kineticalky stable ?

Answer 27

Higher activation energy

Question 28

Thermodynamic feasibility of reaction can be predicted using

Answer 28

Standard electrode potentials

Question 29

Even if reaction feasible it may not take place. Why

Answer 29

Reactants may be kinetically stable Reaction may not take place under standard conditions ( changing conditions may alter Ecell value so reaction takes place if Ecell +ve)

Question 30

Define disproportionation reaction

Answer 30

A reaction in which an element is both oxidized and reduced at the same time

Question 31

Thermodynamically feasible reaction define

Answer 31

A reaction that should take place without any intervention by us, if we consider the enthalpy and entropy changes involved.

Question 32

Ecell is directly proportional to

Answer 32

🔺S total and not 🔺Ssystem

Question 33

Fuel cell with acidic electrolyte anode reaction

Answer 33

H2(g) —> 2H+(aq) + 2e-

Question 34

Fuel cell acidic electrolyte cathode reaction

Answer 34

HalfO2(g) + 2H+(aq) + 2e- ———> H2O(l)

Question 35

Fuel cell alkaline electrolyte anode reaction

Answer 35

H2(g) + 2OH- (aq) ——> 2H2O(l) + 2e-

Question 36

Fuel cell alkaline electrolyte cathode equation

Answer 36

HalfO2(g) + H2O(l) + 2e- ——> 2OH-(aq)

Question 37

Advantages of hydrogen oxygen fuel cells

Answer 37

Higher efficiency Lighter Does not emit green house gases

Question 38

Disadvantages of hydrogen oxygen fuel cell

Answer 38

1.Difficulties transporting and storing 2. The process by which hydrogen is obtained release CO2 3. Higher cost for production

Question 39

Mn+ acidic sol = colorless. Why it’s used as an indicator

Answer 39

As soon as Mn is in excess sol = pink

Question 40

Mn + alkali sol not used. Why?

Answer 40

Mn+7 turns to brown Mn+4 Brown ppt interferes with endpoint colour

Question 41

Overall equation of Mn+7 + iron +2

Answer 41

MnO4-(aq) + 8H+(aq) + 5Fe+2(aq) ——> Mn+2(aq) + 4H2O(l) + 5Fe+3(aq)

Question 42

MnO4- oxidation no is

Answer 42

+7

Question 43

Mn+7 + ethanedioic acid

Answer 43

2MnO4-(aq) + 6H+(aq) + 5H2C2O4(aq) ———> 2Mn+2(aq) + 8H2O(l) + 10CO2(g)

Question 44

Iodine and sodiumthiosulfate equation

Answer 44

2S2O3-2(aq) + I2(aq) ——> S4O6-2(aq) + 2I-(aq)

Question 45

What is the indicator used in sodiumthiosulfate and iodine equation

Answer 45

Starch. sol is deep blue black which disappears at endpoint

Question 46

Starch should not be added to early to titration of sodiumthiosulfate and iodine reaction. Why

Answer 46

Starch iodine complex form which reduce accuracy of titration