Metals and Non-metals

Which of the following methods is suitable for preventing an iron frying pan from rusting?

• Applying grease
• Applying paint
• Applying a coating of zinc
• All of the above.
  Answer: (c) Applying a coating of zinc

An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

• Calcium
• Carbon
• Silicon
• Iron
  Answer: (a) Calcium

Food cans are coated with tin and not with zinc because

• zinc is costlier than tin.
• zinc has a higher melting point than tin.
• zinc is more reactive than tin.
• zinc is less reactive than tin.
  Answer: (c) zinc is more reactive than tin.

You are given a hammer, a battery, a bulb, wires and a switch.

• How could you use them to distinguish between samples of metals and non-metals?
  
  Answer: If a substance can be beaten into thin sheets with the help of a hammer then the given substance is a metal. Otherwise, it is a non-metal. A circuit is made with the help of a battery, a bulb, wires and a switch. After that, the given substance is connected in the circuit. If the given substance ensures that the circuit is complete then it is a metal; else it is a non-metal.
• Assess the usefulness of these tests in distinguishing between metals and non-metals.
  
  Answer: When a substance fulfills both the criteria then it can be confirmed as a metal. We know that some of the metals are brittle and graphite (a non-metal) is a good conductor of electricity. Hence, either of the tests cannot confirm a metal or non-metal; when the test is done in isolation.

What are amphoteric oxides? Give two examples of amphoteric oxides.

Answer: Some oxides show both acidic and basic characters. Such oxides are called amphoteric oxides. Amphoteric oxide reacts with acid as well as with base to form salt.

Example: Aluminium oxide and zinc oxide are examples of amphoteric oxide. When aluminium oxide reacts with a base, it gives salt and water.

Al₂O₃ + 2NaOH ⇨ 2NaAlO₂ + H₂O

When aluminium oxide reacts with an acid it gives salt and water.

Al₂O₃ + 6HCl ⇨ 2AlCl₃ + 3H₂O