C4 - Metallic Structures, Superconductors and Water

Question 1

Give some properties of metals

Answer 1

In general:

• hard
• lustrous
• good conductors of heat and electricity

Many metals have high tensile strength, so they resist being stretched. They also have high melting points and boiling points.

Question 2

Describe how metallic bonding works and how it creates some of the properties of metals.

Answer 2

• Metals contain positive metal ions packed closely together. These form when electrons leave the outer shell of each atom.
• The electrons become free to move and so form a ‘sea’ of delocalised electrons.
• Metallic bonding is the strong force of attraction between the sea of delocalised electrons and the closely packed positive metal ions.
• These forces are strong. It takes a lot of energy to overcome them, which is why metals have high melting points and boiling points.

Question 3

Why do metallic structures contain crystals?

Answer 3

The particles in solid metals are packed closely together in a regular arrangement. This arrangement is repeated many times to produce crystals.

Question 4

How is resistance caused within metals? What does resistance do?

Answer 4

• The metal crystals contain delocalised electrons which are able to move easily through the structure allowing it to conduct electricity.
• However, their path through the metal is not clear. Other electrons and the positive metal ions get in the way. This causes electrical resistance. Resistance makes metals heat up when they conduct electricity, wasting energy.

Question 5

What is a superconductor? What are some uses? What could they be used for in the future?

Answer 5

Superconductors: materials with little or no resistance to the flow of electricity at low temperatures.

Uses:

• powerful electromagnets
• MRI scanners

Future:

• super-fast electronic circuits= extremely powerful computers.
• replace the traditional metal cables that carry electricity from power stations to our homes, offices, and factories. There would be little or no loss of energy from superconducting cables, as they would have little or no resistance.

Question 6

What are the drawbacks of superconductors?

Answer 6

At the moment, superconductors only work at very low temperatures which means that the applications of superconductors are limited.

Question 7

What is an aquifer and what does it contain apart from water?

Answer 7

Underground water reserve. Water from here contains many different dissolved substances. Many of these must be removed to make the water safe to drink or to use in industry.

Question 8

Why is water important for industrial processes?

Answer 8

Can be used as:

• a solvent to dissolve other substances
• a coolant to stop overheating happening
• a cheap raw material.

Question 9

What are some substances and pollutants found in water?

Answer 9

• insoluble materials such as leaves
• dissolved salts and minerals.
• microbes
• various pollutants :
  • nitrates from fertiliser that runs off fields
  • lead compounds from old lead pipes
  • pesticides from spraying crops in fields close to
  water resources.

Question 10

Give two ways in which water can be purified?

Answer 10

1. Sedimentation allows large particles such as sand and soil to settle to the bottom over time. Filtration then removes the ner particles, including clay. Chlorination kills microbes in the water, helping to prevent disease.
2. Very pure water can be produced from sea water by distillation. However, a lot of energy is needed to do this. It is usually too expensive to make large amounts of fresh water in this way.

Question 11

How do you test for sulfate ions? Give the word and symbol equation for this.

Answer 11

• A small sample of the water is put into a test tube, then a few drops of barium chloride solution are added.
• If sulfate ions are present, a white precipitate of barium sulfate forms.

                                                                                        (white precipitate) Sodium sulfate + barium chloride => sodium chloride + barium sulfate
    Na2SO4    +          BaCl2          →       2NaCl             +     BaSO4

Question 12

How do you test for halide ions? What colour precipitates do these form?

Answer 12

• Silver nitrate solution is used to test for dissolved halide ions.
• A small sample of the water is put into a test tube, then a few drops of silver nitrate solution are added.
  • chloride ions produce a white precipitate
  • bromide ions produce a cream-coloured precipitate
  • iodide ions produce a pale yellow precipitate.