Science

Chapter 1

Chemical Reactions and Equations

NCERT Solution

In-text Questions (Page 6)

Question 1: Why should a magnesium ribbon be cleaned before burning in air?

Magnesium is very reactive metal like (Na, Ca, etc.). When it expose to air it reacts with oxygen to form a layer magnesium oxide (MgO) on its surface.

`2Mg+O_{2} \Rightarrow 2MgO`

This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper to remove this layer so that the underlying metal can be used for the reaction.

Concept: Always remember that magnesium being a reactive metal will react with oxygen if kept in open. So, it has to be cleaned before it is burned in air.

Question 2: Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride

`H_{2}+Cl_{2} \Rightarrow 2HCl`

Concept: First convert the word equation into skeletal equation and then balance the different atoms on both sides of the equation.

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(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium Chloride

`3BaCl_{2}+Al_{2}(SO_{4})_{3}\Rightarrow BaSO_{4}+2AlCl_{3}`

Concept: First convert the word equation into skeletal equation and then balance the different atoms on both sides of the equation.

Let’s Draw (Page 58)

Question 1: In the circles below draw—

(Note: Students can also draw a wheel, a moon, a sun or a rabbit in Mohini’s circle).

Question 2: Look at these shapes.Try making these shapes into

  • a car
  • a house
  • a door
  • anything else

Activity to be done by yourself.

Question 3: Draw along the dots. So, what did you make? Can you make sounds like a train?

I made a train by joining the dots. Yes, I can make sounds like a train.

Question 4: Draw a face on the balloon below. One has been done for you.

Let's Read and Write (Page 60)

Question 1:

Question 2:

Question 3: Look at the picture and fill in the blanks.

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