19.5.2 The Stoichiometry of Electrolysis

Question 1

The Stoichiometry of Electrolysis

Answer 1

• The number of electrons passing through a circuit is related stoichiometrically to the amounts of products formed and reactants consumed.

Question 2

note

Answer 2

• Voltage is like water pressure. The total amount of water flowing through a pipe can be calculated by multiplying the flow rate by the time the water is flowing. Similarly, the total amount of charge flowing through a circuit can be calculated by multiplying the current by the time the circuit is running.
• The current flowing through a circuit changes as the
  concentrations of products and reactants change, making the calculation of total charge difficult. A device called a coulombmeter can be used to do these calculations automatically.
• How many grams of iodine are produced when a current of 8.52 mA flows through a cell containing a solution of potassium iodide for 10 minutes?
• To solve this problem, current must first be converted to charge by multiplying by time in seconds. Next, charge is converted to moles of electrons by dividing by the Faraday constant (96,485 C/mol). Moles of electrons are then converted to moles of iodine by the stoichiometric relationship in the oxidation half-reaction, and moles of iodine are converted to grams of iodine.

Question 3

Consider the electrolytic process below

Cu2+(Aq) + 2e- -> Cu(s)

How many grams of copper are produced when a current of 10.0 amps is passed for 0.5 hours through a solution containing copper (II) ions?

Answer 3

5.94 g

Question 4

Consider the electrolytic process below

2I- -> I2 + 2e-

How many grams of iodine are produced at a platinum anode when a current of 8.52 mA is passed for 20 minutes through a sodium containing potassium iodide?

Answer 4

0.013 g

Question 5

A process that occurs without any outside intervention is said to be what?

Answer 5

Spontaneous

Question 6

Which of the following definitions regarding galvanic cells is INCORRECT?

Answer 6

galvanic cell—converts electrical energy to chemical energy

Question 7

Use the table of standard reduction potentials to calculate the Ecell for the following reaction in a galvanic cell:

Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s)

Answer 7

+1.10 V

Question 8

Examine the diagram of the copper / silver galvanic cell below.

Which of the following statements is true?

Answer 8

Ions from the salt bridge migrate to maintain a neutral electric charge.

Question 9

Which instrument would be the best choice to measure the total amount of current passing through a wire in a galvanic cell?

Answer 9

Coulometer

Question 10

Examine the diagram of the copper / silver galvanic cell below.

Which of the following statement is incorrect?

Answer 10

For every mole of electrons leaving the anode, one mole of copper(II) ions go into solution in the cathode

Question 11

Which of the following reactions would occur only in a galvanic cell?

Answer 11

O2(g) + 4H+(aq) + 2Ni(s) -> 2H2O(l) + 2Ni2+(aq)

Question 12

Which of the following reactions would occur only in an electrolytic cell?

Answer 12

2Zn2+(aq) + 4OH-(aq) -> 2Zn(s) + O2(g) + 2H2O(l)