Redox II

Question 1

Describe oxidation using oxidation numbers

Answer 1

An increase in oxidation numbers means the reaction is oxidized

Question 2

Describe reduction using oxidation numbers

Answer 2

An decrease in oxidation numbers means the reaction is reduced

Question 3

Describe the redox reactions that occur with s-block elements

Answer 3

• They are usually metals
• They tend to be oxidized because
• They lose electrons to form positive ions with the charges

Question 4

Describe the redox reactions that occur in the p block

Answer 4

• They are both metals and nonmetals
• The metals lose electrons and form a positive ion which makes them oxidized
• The non-metals gain electrons and form a negative ion which makes them reduced

Question 5

Describe the redox reactions that occur in the d block

Answer 5

• They are metals
• They have variable oxidation states like transition metals
• They tend to form positive ions with positive oxidation

Question 6

What is meant by the term ‘standard electrode potential’, Eo

Answer 6

The standard electrode potential of a half-cell is the voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

Question 7

What are the standard electrode potential conditions

Answer 7

• concentration of 1 moldm^-3
• Pressure of 100kPa or 1atm
• temperature at 298k

Question 8

Why is a reference standard hydrogen electrode necessary ?

Answer 8

• The standard hydrogen electrode (SHE) serves as a crucial reference point because it has a known and consistent standard reduction potential of 0 volts.
• This allows scientists to measure and compare the reduction potentials of other half-cells accurately.
• Additionally, the SHE provides a stable environment for comparison, as hydrogen ions and a platinum electrode in contact with a hydrogen gas at a known pressure create a standardized reference point against which other half-cell potentials can be measured.

Question 9

What is the formula for cell potential

Answer 9

Ereduction - Eoxidation

Question 10

Oxidation takes place at which electrode

Answer 10

Anode with a (- charge)

Question 11

Reduction takes place at which electrode

Answer 11

Cathode with a (+ charge)

Question 12

The more reactive the metal the

Answer 12

more readily it gives up electrons hence that means more reactive metals are oxidized and made the anode

Making less reactive metals the cathode in that electrochemical cell

Question 13

Describe how the electrodes in an electrochemical cells diagram is usually drawn

Answer 13

Anode left (Oxidation takes place here)
Cathode right (Reduction takes place here )

Question 14

How do electrons flow in electrochemical cells

Answer 14

Electrons move from most reactive to least reactive

Question 15

What is EMF

Answer 15

Voltage between two half cells

Question 16

How to set up an electrochemical cell

Answer 16

1. Prepare Electrodes: Obtain metal strips for each electrode and clean their surfaces with sand paper to ensure they are free from impurities.
2. Remove Grease: Clean the electrodes further with propanone to remove any grease or oil, ensuring no contamination from handling.
3. Immerse in Ion Solutions: Place each electrode in a beaker filled with a solution containing ions of the respective metal. For instance, zinc metal goes into ZnSO4(aq), and copper into CuSO4(aq). Add acid if one half-cell contains an oxidizing agent like MnO4–.
4. Salt Bridge Creation: Use a salt bridge to connect the two solutions. Soak a piece of filter paper in a salt solution like KCl(aq) or KNO3(aq) and place it between the beakers, ensuring the ends are immersed in the solutions.
5. Connect to Voltmeter: Use crocodile clips and wires to connect the electrodes to a voltmeter. A correct setup should yield a voltage reading on the voltmeter, allowing for the measurement of cell potential.

Question 16

What do voltmeters measure

Answer 16

Direction of flow of electrons

Question 17

Why shouldn’t we handle the electrode with our hands after sand papering and dipping in propanone

Answer 17

To avoid transfer of grease from hand

Question 18

What is the role of a salt bridge ?

Answer 18

• It completes the circuit
• It also allows for the salt ions to flow between the half-cells to balance the changes

Question 18

An oxidizing agent that contains oxygen will have to be

Answer 18

acidified like (MnO4^-) in acidified potassium manganate

Question 19

Define electrode potential

Answer 19

This is a measure of how easily the substance in the half-cell is oxidized (i.e. loses electrons)

Question 20

What creates potential difference in half cells

Answer 20

It occurs due to the difference
in charge between the electrode and the ions in solution
Positive ions formed negatively charged electrode

Question 21

What is the equation of the reaction of hydrogen electrodes ?

Answer 21

2H+(aq) + 2e– <—-> H2(g)

Question 22

Why are standard conditions used to measure electrode potentials

Answer 22

• Just like any other reversible reaction, the equilibrium position in a half-cell is affected by changes in temperature, pressure and concentration.
• Changing the equilibrium position changes the cell potential.
• Using standard conditions means you always get the same value for the electrode potential and you can compare values for different cells.

Question 23

More reactive metals….

Answer 23

• The more reactive a metal is, the more easily it loses electrons to form a positive ion.
• More reactive metals have more negative standard electrode potentials.

Question 24

The more reactive a non-metal is

Answer 24

• The more easily it gains electrons to form negative ions
  -More reactive non-metals have more positive standard electrode potentials

Question 25

A thermodynamically feasible reaction would have an overall ………. potential

Answer 25

positive

Question 26

How do you determine if a rection is a disproportionation one with electrode potentials

Answer 26

A positive overall cell potential means the reaction can proportionate

Question 27

Why would predictions using electrode potentials be inaccurate

Answer 27

• Because the prediction is done under standard conditions if it is not under standard conditions we would get different values
• It could also be because the reaction kinetics are not favorable. This means :
  1
  1.The rate of a reaction may be so slow that the reaction might not appear to happen.
  2. If a reaction has a high activation energy, this may stop it happening.

Question 28

Cell potential is directly proportional to

Answer 28

Entropy and Equilibrium Constant