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Extra e) Separate a mixture of sand and water (sea water)

Ans: Filtration

f) Obtain pure water from salt solution (or sea water)

Ans: Simple distillation

g) Obtain sugar from sugarcane

Ans: Crystallisation

h) Produce pure oxygen and pure nitrogen gas from liquid air

Ans: Fractional distillation

Q3. A child accidentally puts the sand into a bottle of granulated sugar.

Explain how you can separate the sand from the granulated sugar?

Ans: The sand can be separated using filtration method.

Process used in filtration method:

i) At first, we dissolve the mixture of sand and granulated sugar into

water.

ii) Then we pour the mixture of sand and sugar solution into a filterfunnel lined with a filter paper.

iii) The insoluble sand is then trapped on the filter paper.

iv) The sugar solution passes through the funnel.

Thus, we can separate sand from granulated sugar.

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CHAPTER 5

Energy and Chemical Changes

Q1. What is meant by (a) an electrolyte and (b) a cation?

Ans:

(a) Electrolyte: An electrolyte is a compound which conducts electricity in

molten or liquid state (aqueous solution).

Example, molten Lead (II) Chloride or aqueous Copper (II) Chloride

solution.

(b) Cation: A cation is a positive ion which is attracted to the cathode (or

negative electrode) and also is discharged at the cathode duringelectrolysis.

Example, Copper ions are discharged at the cathode and become

copper atoms .

Q2. State two differences between a molten electrolyte and an aqueous

electrolyte.

Ans:

Differences between molten electrolyte and aqueous electrolyte:

Molten Electrolyte Aqueous Electrolyte

1. When an electrolyte is heatedto its melting point, it forms amolten electrolyte.

1. When an electrolyte isdissolved into water, it forms anaqueous electrolyte.

2. It is generally an ionic

compound.

2. It is generally a salt solution.

3. It is less energy efficient. 3. It is more energy efficient.

Note: You must memorize no. 1 and can choose anyone between no. 2

and no. 3.

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Q3. Give three uses of Electrolysis.

Ans: Three uses of electrolysis:

Electrolysis is used to --

i) extract metals from their oresii) obtain pure metals by removing impurities from impure metals

iii) coat a metal object with a layer of another metal (electroplating).

Q4. In the metal plating process what is used as the anode and the

cathode?

Ans:

In metal plating or electroplating process, for example in copper platingprocess, Copper (Cu) is used as anode and Iron (Fe) is used as cathode.

Likewise, in silver plating process, Silver (Ag) is used as anode and

Aluminium (Al) is used as cathode.

Q5. What is produced at the anode and at the cathode in the electrolysis of

molten lead (II) bromide?

Ans:

In the electrolysis of molten lead (II) bromide,

(a) Brown bromine gas is released

at the anode. It can change blue

litmus paper to red and

decolourises it.

(b) Grey shiny lead atoms are

deposited at the cathode.

Figure: Electrolysis of molten lead (II) bromide

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CHAPTER 6

Nuclear Energy

Q1. How can the process of nuclear fusion be accelerated?

Ans: The process of nuclear fusion can be accelerated by achieving high

temperature and pressure. This accelerates the speed of colliding

hydrogen neutrons and hence accelerates the process of nuclear fusion.

Extra Q1. How can the process of nuclear fission be accelerated?

Ans: The process of nuclear fission can be accelerated by using graphite

core. The graphite core slow down the speed of neutrons and the fission ofuranium - 235 is more likely to occur with slow-moving neutrons compared

to fast moving neutrons.

Q2. How can the rate of chain reactions (nuclear fission) in a nuclear

reactor be controlled?

Ans: The rate of nuclear reaction can be controlled by using boron rods.

The boron rods inside a nuclear reactor absorb neutrons. This can controlthe number of neutrons that bombard the uranium235 nuclei.

Extra Q2. How can the rate of nuclear fusion be controlled?

Ans: The rate of nuclear fusion can be controlled by using magnetic field to

confine the plasma hydrogen nuclei.

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Q3. State the type of energy sources that are non-renewable.

Ans: Types of non-renewable energy sources:

Non-renewable energy sources are mainly fossil fuels such as,

i) Crude oil / Petroleumii) Natural gas

iii) Coal

All these are non-renewable and have been gathered down the Earths

crust for millions of years.

Q4. Name the radioactive substances used in nuclear reactors to producenuclear energy.

Ans: Radioactive substances used in nuclear reactors:

i) Uranium - 235 nucleus (used in nuclear fission)

ii) Hydrogen - 2 (Deuterium) or Hydrogen3 (Tritium) nuclei (used in

nuclear fusion)

Q5. What is the main use of nuclear energy produced from nuclear fission?

Ans: Use of nuclear fission energy:

Nuclear energy produced from nuclear fission is used to

i) generate electric energy

ii) propel submarines and big vessels

iii) operate satellites

iv) explode atomic bombs

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Extra Q5. What is the main use of nuclear energy produced from nuclear

fusion?

Ans: Use of nuclear fusion energy:

Nuclear energy produced from nuclear fusion is used toi) produce hydrogen bombs

ii) produce heat and light energy from the Sun

Q6. State a misuse of nuclear energy that can bring mass destruction to

nature and mankind.

Ans:

Using nuclear energy in atomic bomb and hydrogen bomb explosion canbring mass destruction to nature and mankind.