ICSE Class 6 Chemistry Important Questions Chapter 8 Rocks and Minerals

Chemistry ICSE Class 6 Important Questions Chapter 8 Rocks and Minerals

Practice Questions

Question 1.
Write use of –

1. Granite
2. Pumice
3. Basalt
4. Limestone
5. Quartzite
6. Obsidian

Answer:

1. Use of Granite – It is used for making monuments and decorating buildings.
2. Use of Pumice – It is used in the cosmetic industry as an abrasive. It is also used by dentists for polishing teeth.
3. Use of Basalt – It has sharp edges and is therefore used for making tools.
4. Use of Limestone – It is used to make quicklime, mortar, cement and concrete.
5. Use of Quartzite – Because of its hardness, it is used as paving stones and railway ballast.
6. Use of Obsidian – Used in surgical operations as the edges of this rock are very sharp.

Question 2.
What is magma and lava ?
Answer:
Magma is the hot molten rock deep within the earth. During volcanic eruption, when the magma appears above the earth, itis called lava.

Question 3.
How are rocks classified on the basis of their mode of occurrence ?
Answer:
Igneous rocks are classified into the following two types based on their mode of occurrence.

1. Extrusive igneous rocks :
They are formed by the rapid cooling of molten lava on the earth’s surface. Hence, these rocks are smooth, crystalline and fine-grained. They are also called volcanic rocks. An example of such rocks is basalt.

2. Intrusive igenous rocks :
They are formed when the magma solidifies at a slow rate below the surface of the earth. Hence, the crystals formed in the rock are large-grained in size. Such kinds of rocks with large-sized crystals are known as plutonic rocks. Dolerite and granite are examples of such rocks.

Question 4.
Name some common metamorphic rocks and the rocks they are formed from.
Original rock Metamorphic rock
Granite – Gnesis
Basalt – Schist
Sandstone – Quartzite
Limestone – Marble
Shale – Slate or schist

Question 5.
What is the chemical name of talc and write its use ?
Answer:
Talc is chemically magnesium silicate. It is the softest mineral and used as talcum powder, as a filler in the paper industry, for making ceramics, paint, etc.

Question 6.
What is a streak ?
Answer:
When we rub a mineral on the back of porcelain, it leaves a streak. This streak is specific for a particular mineral and always remains the same. The colour of the streak is a reliable clue in identifying a mineral. Example: Gypsum gives a white streak although it is yellowish in colour.

Question 7.
What are the types of gemstones ?
Answer:
Gemstones are classified as :
1. Precious gemstones – They rare and include highly prized gemstones like diamond, emerald, ruby, sapphire.
2. Semi – Precious gemstones – These are less rare and include garnet, opal, amethyst, jade, lapis, malachite, etc.

Question 8.
Write the colour of the following gemstones :
1. Ruby
2. emerald
3. sapphire
Answer:
1. Ruby – red
2. Emerald – green
3. Sapphire – blue or yellow

Question 9.
Write few uses of coal.
Answer:

1. It is used as a domestic fuel.
2. It is used in the extraction of metals.
3. Used in the generation of electricity.
4. Used for the manufacture of coke and coal gas.
5. Used in the manufacture of synthetic petrol.

Question 10.
Why is natural gas considered an ideal fuel ?
Answer:
Natural gas (methane) bums with a blue smokeless flame and does not leave any ash behind after burning. So, natural gas is considered an ideal fuel.

Methane (natural gas) + oxygen (air)
↓
Combustion
↓
Carbon dioxide + water + heat + light

Question 11.
Why CNG is considered a clean fuel to run vehicles ?
Answer:
CNG is a clean fuel because it does not emit sulphur and lead and causes very low level of air pollution.

Question 12.
Write a short note on petroleum gas.
Answer:
Petroleum gas when liquefied under pressure is called liquefied petroleum gas (LPG). It consists mainly of butane and propane. Pure LPG is odourless. Therefore, to detect its leakage, a strong smelling compound called ethyl mercaptan is added to it. LPG is mainly used as a domestic fuel for cooking. It is stored and supplied in gas cylinders.

Question 13.
Name few renewable sources of energy.
Answer:
Hydroelectric energy, solar energy, wind energy, biomass fuel, nuclear energy, geothermal energy, etc.

ICSE Class 6 Chemistry Important Questions