Electrolysis

Question 1

Do aqueous solutions of weak acids have higher or lower ph than solutions of strong acids that have the same concentration?

Answer 1

They have a higher ph

Question 2

What is the order of magnitude for ph?

Answer 2

As the ph decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10.

Question 3

Examples of weak acids

Answer 3

Ethanoic acid, citric acid, carbonic acid

Question 4

Examples of strong acids

Answer 4

Hydrochloric acid. nitric acid, sulfuric acid

Question 5

Why must acids dissolve in water before they show their acidic properties?

Answer 5

This is because in water acids ionise (split up) to from H+ ions and negative ions. Strong acids ionise completely in solution. In weak acids, most of the molecules stay as they are and don’t release H ions into the solution.

Question 6

Can strong or weak acids be partially reversible when ionising?

Answer 6

Weak acids as they don’t release all of the H ions into the solution. Not all ionised.

Question 7

How are ph values related to the concentration of H+ (aq) ions?

Answer 7

As the concentration of hydrogen ions decreases by a factor of 10 the ph value increases by one unit and vice versa.

Question 8

What is electrolysis?

Answer 8

Electrolysis breaks down a substance using electricity.

Question 9

What is an electrolyte?

Answer 9

The compound that is broken down by electrolysis.

Question 10

Name the ends of electrode

Answer 10

The positive electrode is called the anode and the negative electrode is called the cathode

Question 11

What are the electrodes made of?

Answer 11

Electrodes are usually made of unreactive (inert) substances such as graphite.

Question 12

What happens during electrolysis?

Answer 12

During electrolysis positively changed ions move to the cathode. At the same time the negative ions move to the anode as opposite charges attract.

Question 13

Why do ionic compounds have to be electrolysed once molten or dissolved in water?

Answer 13

Because then the ions are free to move and carry charge to their electrodes.

Question 14

What happens to the ion’s electrons when they reach an electrode?

Answer 14

When the ions reach the electrodes, they lose their charge and become elements. At the electrodes, gases may be given off or metals deposited.

Question 15

What is reduction and oxidation?

Answer 15

Gaining electrons = reduction. Losing electrons = oxidation.

Question 16

What is usually produced at the cathode?

Answer 16

When electrolysis happens in aqueous solution. The less reactive element, either hydrogen or the metal is usually produced at the cathode. At the anode, you get either oxygen gas if the electrolysis is happening in aqueous solution, or a halogen if the electrolyte is a solution of a halide.

Question 17

What is electrolysed in the extraction of aluminium metal?

Answer 17

Aluminium oxide

Question 18

How do we lower the melting point of the aluminium oxide when doing electrolysis?

Answer 18

The aluminium oxide is mixed with molten cryolite to lower its melting point, reducing the energy needed to extract the aluminium. Aluminium forms at the cathode and oxygen forms at the anode.

Question 19

Why do the anodes need replacing over time?

Answer 19

The carbon anodes are replaced regularly as they gradually burn away as the oxygen reacts with the hot carbon anodes, forming carbon dioxide gas.

Question 20

What happens when you electrolyse sodium chloride solution?

Answer 20

When you electrolyse sodium chloride solution, chlorine gas and hydrogen gas given off at the electrodes, plus sodium hydroxide solution (an alkali) left in solution.