Electrochemistry

Question 1

What is a redox reaction?

Answer 1

A redox reaction is a transfer of electrons in a chemical reaction.

Question 2

What is the loss of electrons called?

Answer 2

The loss of electrons is called oxidation.

Question 3

What is the gain of electrons called?

Answer 3

The gain of electrons is called reduction.

Question 4

What does an oxidising agent do?

Answer 4

An oxidising agent accepts electrons and itself gets reduced.

Question 5

What does a reducing agent do?

Answer 5

A reducing agent donates electrons and itself gets oxidised.

Question 6

What is the main rule about elements when it comes to oxidation numbers?

Answer 6

All elements are treated as ions, even if they are covalently bonded.

Question 7

What oxidation number do all uncombined elements have?

Answer 7

All uncombined elements have an oxidation number of 0 (zero).

Question 8

What oxidation number do elements bonded to the same atoms have?

Answer 8

Identical elements that are bonded to each other, like oxygen, have an overall oxidation number of 0 (zero).

Question 9

What is the oxidation number of a simple monoatomic ion?

Answer 9

A simple monoatomic ion has an oxidation number that is the same as its overall charge, for example, Na + has a charge of +1.

Question 10

What is the oxidation number of a complex ion or compound?

Answer 10

The oxidation number of a complex ion or compound is equal to its charge.

Question 11

How do you calculate the oxidation number of an element in a neutral compound?

Answer 11

The overall charge of a neutral compound is 0 (zero). You take away all of the charges and oxidation numbers of elements and ions in the compounds.

Question 12

What charge does combined oxygen always carry?

Answer 12

Combined oxygen always has a charge of -2, except in peroxides, where its -1.

Question 13

What is disproportionation?

Answer 13

Disproportionation is whereby a single element in a single species is simultaneously oxidised and reduced. For example, in the following reaction, the chlorine in NaOCl is oxidised and simultaneously reduced: 3NaOCl —-> NaClO3 + 2NaCl

Question 14

When is a reaction not a disproportionation reaction?

Answer 14

It is not a disproportionation reaction when two different species are simultaneously oxidised and reduced, it must be the same element** in the **same species.

Question 15

The total increase in the oxidation number of the reducing agent must equal…

Answer 15

…the total change in the oxidation number of the oxidising agent.

Question 16

A reducing agent is…

Answer 16

…reduced.

Question 17

An oxidising agent is…

Answer 17

oxidised.

Question 18

What is the standard electrode potential?

Answer 18

The standard electrode potential of any cell is the electrical potential of a cell relative to a standard hydrogen electrode, where all solution are at a concentration of 1 mol dm-3 and any gases are contained at 1 atmosphere at 25 degrees Celsuis.

Question 19

What are the values of electrode potentials always stated as?

Answer 19

The values of electrode potentials are always stated as reduction potentials.

Question 20

On which side do the electrons sit in a reduction potential?

Answer 20

The electrons must always sit on the left-hand side.

Question 21

What is the hydrogen electrode used for?

Answer 21

The hydrogen electrode is used as a reference electrode in all electrochemical measurements.

Question 22

What is the value of the hydrogen electrode at 25C˚?

Answer 22

The value of the standard hydrogen electrode at 25C˚ is zero volts (≠0).

Question 23

What does a standard hydrogen electrode look like?

Answer 23

Hydrogen gas at 1 atm of pressure is passed over a platinum electrode dipped into a solution of 1.0 mol dm-3 solution containing hydrogen ions, for example, hydrochloric acid.

Question 24

How is the voltage of the half cell measured?

Answer 24

The voltage of the half cell is measured by attaching the standard hydrogen electrode to the voltmeter and attaching the other half cell to the other side of the voltmeter. The voltage that reads is equal to the potential being generated in the half cell (not the hydrogen cell).

Question 25

How do you set up a half cell?

Answer 25

You need:

• A solid catalyst, for example, a piece of platinum foil.
• A solution containing the ions, with a concentration of 1.0 mol dm-3.
• A salt bridge to allow electrons to flow between solutions.
• A voltmeter to attach to the electrode, which will tell you what voltage is being read.