Redox II Flashcards
Describe oxidation using oxidation numbers
An increase in oxidation numbers means the reaction is oxidized
Describe reduction using oxidation numbers
An decrease in oxidation numbers means the reaction is reduced
Describe the redox reactions that occur with s-block elements
- They are usually metals
- They tend to be oxidized because
- They lose electrons to form positive ions with the charges
Describe the redox reactions that occur in the p block
- 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
Describe the redox reactions that occur in the d block
- They are metals
- They have variable oxidation states like transition metals
- They tend to form positive ions with positive oxidation
What is meant by the term ‘standard electrode potential’, Eo
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
What are the standard electrode potential conditions
- concentration of 1 moldm^-3
- Pressure of 100kPa or 1atm
- temperature at 298k
Why is a reference standard hydrogen electrode necessary ?
- 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.
What is the formula for cell potential
Ereduction - Eoxidation
Oxidation takes place at which electrode
Anode with a (- charge)
Reduction takes place at which electrode
Cathode with a (+ charge)
The more reactive the metal the
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
Describe how the electrodes in an electrochemical cells diagram is usually drawn
Anode left (Oxidation takes place here)
Cathode right (Reduction takes place here )
How do electrons flow in electrochemical cells
Electrons move from most reactive to least reactive
What is EMF
Voltage between two half cells
How to set up an electrochemical cell
- Prepare Electrodes: Obtain metal strips for each electrode and clean their surfaces with sand paper to ensure they are free from impurities.
- Remove Grease: Clean the electrodes further with propanone to remove any grease or oil, ensuring no contamination from handling.
- 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–.
- 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.
- 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.
What do voltmeters measure
Direction of flow of electrons
Why shouldn’t we handle the electrode with our hands after sand papering and dipping in propanone
To avoid transfer of grease from hand
What is the role of a salt bridge ?
- It completes the circuit
- It also allows for the salt ions to flow between the half-cells to balance the changes
An oxidizing agent that contains oxygen will have to be
acidified like (MnO4^-) in acidified potassium manganate
Define electrode potential
This is a measure of how easily the substance in the half-cell is oxidized (i.e. loses electrons)
What creates potential difference in half cells
It occurs due to the difference
in charge between the electrode and the ions in solution
Positive ions formed negatively charged electrode
What is the equation of the reaction of hydrogen electrodes ?
2H+(aq) + 2e– <—-> H2(g)
Why are standard conditions used to measure electrode potentials
- 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.
More reactive metals….
- 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.
The more reactive a non-metal is
- The more easily it gains electrons to form negative ions
-More reactive non-metals have more positive standard electrode potentials
A thermodynamically feasible reaction would have an overall ………. potential
positive
How do you determine if a rection is a disproportionation one with electrode potentials
A positive overall cell potential means the reaction can proportionate
Why would predictions using electrode potentials be inaccurate
- 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.
Cell potential is directly proportional to
Entropy and Equilibrium Constant
