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Some examples from this set of practice questions
1.
How do you calculate the standard electrode potential of a cell?
Answer: Standard electrode potential of a cell = E(reduction) - E(oxidation)
2.
What are the conditions for a standard electrochemical cell?
Answer: Temperature 298 K Concentrations of all aqueous solutions at 1mol/dm3 Pressure of gases = 1 atmosphere
3.
How is the salt bridge made?
Answer: By dipping a strip of filter paper into a potassium nitrate solution (KNO3).
4.
What are the main components of an electrochemical cell that is used to measure the standard electrode potential of zinc (Zn)?
Answer: A voltmeter, a salt bridge, a Zn rod immersed into a Zn ion aqueous solution with concentration 1mol/dm3, a standard hydrogen electrode: hydrogen gas pumped into a tube that is immersed into H+ solution with concentration 1mol/dm3 and platinum half immersed into the solution (in contact with the gas and the aqueous solution).
5.
How do you determine in which direction in an electrochemical cell do electrons flow?
Answer: The half-cell with the more positive standard electrode potential (see the data booklet) is the positive electrode. At the positive electrode reduction occurs, or the gain of electrons. So electrons from from the negative electrode to the positive one.
6.
What happens when the concentration of the Zn ion is increased in its half-equation? What happens when it is decreased?
Answer: 1. When concentration of Zn ion increases, equilibrium shifts to the right to decrease the concentration of the ion. Gaining of electrons is reduction and the values of the standard electrode potentials for reduction reactions are more positive. So the electrode potential with also become more positive. 2. When concentration of Zn ion decreases, equilibrium shifts to the left to increase the concentration of the ion. Zn (s) will lose electrons, will get oxidised and the values of the standard electrode potentials for oxidation reactions are more negative. So the electrode potential with also become more negative.
7.
List the anions in their increasing order of ease of discharge/oxidation. (hardest to easiest)
Answer: sulfate, nitrate, chloride, hydroxide, bromide, iodide or SO4-, NO3-, Cl-, OH-, Br-, I- (sonoclohbri)
8.
How does ease of discharge of cation change with their standard electrode values?
Answer: Ease of discharge of cations at the cathode increases as their standard electrode values increase/become more positive.
9.
What is the Faraday constant and what is its value?
Answer: Faraday constant is the charge of one mole of electrons. F = 96 500 C (coulombs)
10.
What is the formula connected the Avogadro constant L, the Faraday constant F and the charge of one electron \'q\'?
Answer: L = F/q
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