Electrolysis and Extraction

Question 1

Practical: Investigate the Electrolysis of Aqueous Solutions

Answer 1

1. Add the aqueous solution to a beaker and cover the electrodes with the solution
2. Invert two test tubes to collect gaseous products
3. Connect the electrodes to a power supply using wires and crocodile clips
4. Turn on power pack
5. Make observations at each electrode
6. Gases collected in the test tubes can be tested and identified
7. If a solid forms around the electrode, it must be a metal. The colour can indicate the metal

Question 1

Cathode products in electrolysis of aqueous solutions

Answer 1

Metal or hydrogen ion will form solid metal or hydrogen gas

The metal will be produced if it is less reactive than hydrogen
Hydrogen gas will be produced if the metal is more reactive than hydrogen

Question 2

Anode products in electrolysis of aqueous solutions

Answer 2

• Halide solutions form its halogen
• Sulfate, nitrate or hydroxide solutions form oxygen

Question 3

Ore

Answer 3

Rocks that have enough mineral to extract

Question 4

Native metals

Answer 4

Very unreactive metals that are found in the Earth’s crust as the uncombined element (not bonded to other elements)

Question 5

Method of metal extraction vs reactivity

Answer 5

• Metals more reactive than carbon, such as aluminium, are extracted by electrolysis
• Metals less reactive than carbon, such as iron, may be extracted by reduction with carbon
• Unreactive metals such as gold are found as a native metal

Question 6

Carbon extraction method

Answer 6

• Add two spatulas of charcoal into a test tube
• Add two spatulas of metal oxide
• Mix well
• Add one spatula of charcoal on top of the mix
• Heat strongly with a bunsen burner
• Allow to cool and examine products

Question 7

Uses of aluminium

Answer 7

• airplane bodies (low density, high resistance of corrosion)
• power cables (good conductor of electricity)
• saucepans (good conductor of heat, corrosion-resistant)
• food cans (non-toxic, corrosion-resistant)

Question 8

Uses of copper

Answer 8

• hospital surfaces (antimicrobial properties)
• electrical wires (good conductor of electricity, ductile)
• water pipes (unreactive, malleable)
• pots and pans (good conductor of heat, unreactive, malleable)

Question 9

Uses of mild steel (0.25% carbon)

Answer 9

• nails
• car bodies
• ships

Advantages:
- strong
- malleable
- cheap

Disadvantage:
- rusts easily

Question 10

Uses of high-carbon steel (0.6% - 1.2% carbon)

Answer 10

• cutting tools
• masonry nails
• knives

Advantages:
- harder than mild steel
- resistant to wear

Disadvantage:
- brittle

Question 11

Uses of stainless steel (<1.2% carbon)

Answer 11

• cutlery
• cooking utensils
• kitchen sinks

Advantages:
- corrosion-resistant
- strong
- hard

Disadvantages:
- expensive
- may not be as durable as other materials

Question 12

Uses of iron

Answer 12

• buildings (strong)
• saucepans (malleable, good conductor of heat)
• alloyed with carbon, nickel, chromium etc. to form cast iron or steel

Question 13

Alloy

Answer 13

A mixture of a metal and one or more elements, usually other metals or carbon

Question 14

Why alloys are harder than pure metals

Answer 14

In an alloy, there are atoms of different sizes. The smaller or bigger atoms distort the layers of atoms in the pure metal from its lattice. This means that a greater force is required for the layers to slide over each other.

Question 15

Electrolysis of molten lead bromide

Answer 15

• solid lead bromide is heated and becomes molten
• electrodes attached to a power source are placed in the molten lead bromide
• electrodes become charged, forming cathode and anode
• At the anode a red-brown gas is given off (bromine gas)
  explanation: negatively charged bromide ions are attracted to the anode. There, bromide ions lose electrons (oxidation) and become bromine atoms
• At the cathode a shiny substance is formed (molten lead)
  explanation: positively charged lead ions are attracted to the cathode. There, lead ions gain electrons (reduction) and become lead atoms

Question 16

Electrolysis of sodium chloride solution

Answer 16

• solid sodium chloride is dissolved in water
• the solution also contains hydrogen ions (H+) and hydroxide ions (OH–) from ionised water
• chloride ions (Cl–) and hydroxide ions (OH–) are attracted to the anode
• sodium ions (Na+) and hydrogen ions (H+) are attracted to the cathode
• at the anode a green gas is given off (Cl2(g))
• at the cathode a colourless gas is given off (H2(g))
• the solution at the end is sodium hydroxide (NaOH(aq))

Question 17

Electrolysis of copper sulfate solution

Answer 17

• copper sulfate solution is composed of copper ions (Cu2+), sulfate ions (SO42-), hydrogen ions (H+) and hydroxide ions (OH–)
• at the cathode a brown layer is formed. This is copper.
• at the anode, bubbles of gas are given off. This is oxygen gas (O2(g))
  explanation: hydroxide ions lose electrons (oxidation) and form molecules of oxygen and water. The hydroxide ions react at the anode instead of the sulfate ions because the hydroxide ions are less stable

Question 18

Electrolysis of sulfuric acid

Answer 18

• sulfuric acid is composed of sulfate ions (SO42-), hydrogen ions (H+) and hydroxide ions (OH–)
• at the cathode bubbles of gas are formed. This is hydrogen gas (H2(g))
• at the anode, bubbles of gas are given off. This is oxygen gas (O2(g))

Question 19

Electrolysis

Answer 19

The breaking down of a substance using electricity. An electric current is passed through an electrolyte (a molten or dissolved ionic compound), causing it to decompose.