Question 1: Which of the following pairs will give displacement reactions?
Explanation: Copper is more reactive than silver. So, copper will displace silver from silver nitrate solution. Copper is less reactive than sodium, so option a is ruled out. Aluminium is less reactive than magnesium, so option b is ruled out. Silver is less reactive than iron, so option c is ruled out.
Question 2: Which of the following methods is suitable for preventing an iron frying pan from rusting?
Explanation: Grease will get wiped off while cleaning. Both grease and paint will be burnt while cooking. A coat of zinc does not pose these problems.
Question 3: 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
Explanation: Carbon is a non-metal, and oxides of metal do not have high melting point. Rest of the options are metals but out of them only oxide of calcium is soluble in water. So, calcium is the correct answer.
Question 4: Food cans are coated with tin and not with zinc because
Question 5: You are given a hammer, a battery, a bulb, wires and a switch.
(a) 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.
(b) 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.
Question 6: 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
Copyright © excellup 2014