Saturday, 11 April 2020

CBSE Class 10 - Chemistry - CHEMICAL REACTIONS AND EQUATIONS (Q & A) - Understanding Chemical Changes (#eduvictors)(#cbse)(#class10Chemistry)

Understanding Chemical Changes 

CBSE Class 10 - Chemistry

Q1: What is a chemical change?

Answer: A chemical change is one in which a new substance is formed which has properties totally different from the starting materials. The starting materials are called as reactants and the new substances formed are called as products. In such changes, the nature and identity of the products is completely changed.

Q2: Give three examples of chemical change?

Answer: Examples of chemical changes occurring in our daily life –
     ❑ Cooking of food
     ❑ Rusting of iron
     ❑ Digestion of food
     ❑ Respiration
     ❑ Souring of milk

Q3: What are the characteristics or indicators of a chemical change?

Answer: Characteristics or indicators of a chemical change are:
     ❑ Change in Physical State
     ❑ Change in colour
     ❑ Evolution of gas
     ❑ Change in temperature
     ❑ Formation of precipitate

Q4: Give two examples of change in physical state during a chemical change.

o Solid wax burns to form carbon dioxide and water vapour which are gaseous.
o Petrol which is a liquid burns to form carbon dioxide and water vapour which are gaseous.

Q5: Give two examples of chemical change in which change in colour occurs.

o Rusting of iron – Greyish-black iron changes to reddish-brown rust.
o Blue coloured copper sulphate solution reacts with iron filings to form green coloured ferrous sulphate solution and copper

Q6: Give examples where evolution gas indicates that chemical change has occurred.

o Burning of coal leads to the formation of carbon dioxide gas.
o Reaction between calcium carbonate and hydrochloric acid results in the formation of carbon dioxide gas.
o Reaction between zinc dust and sulphuric acid leads to the formation of hydrogen gas.

Q7: Give examples of chemical changes in which change in temperature takes place.

o Zinc dust is added to sulphuric acid, the beaker becomes warm. (Increase in temperature - Exothermic Change)
o Reaction between barium hydroxide and ammonium chloride causes the beaker to become cold. (Decrease in temperature - Endothermic Change)

Q8: What is a precipitate? Give an example of chemical change where precipitate formation takes place.

Answer: An insoluble substance formed on mixing two salt solutions is a precipitate.
For example, When lead nitrate solution reacts with potassium iodide solution, a yellow precipitate of lead iodide appears.

Q9: State one characteristic each of the chemical reaction which takes place when :
1. dilute hydrochloric acid is added to sodium carbonate
2. lemon juice is added gradually to potassium permanganate solution
3. dilute sulphuric acid is added to barium chloride solution
4. quicklime is treated with water
5. wax is burned in the form of a candle

1. Evolution of carbon dioxide gas
2. Change in colour from purple to colourless
3. Formation of white precipitate of barium sulphate
4. Change in temperature
5. Change in state from solid to liquid and gas.

Q10: Does chemical change show only indicator at a time?

Answer: No, usually a chemical change involves more than one indicators. For example,When zinc reacts with dilute sulphuric acid, a gas is evolved namely hydrogen and also a rise in temperature takes place.

☞See Also:

Ch 1 - Chemical Reactions & Equations  (Q &A)
Ch 1 - Chemical Reactions & Equations (MCQs)
Ch 1 - Chemical Reactions & Equations (Board Questions)
Learn about Chemical Formulae
Ch1 - Chemical Reactions & Equations (Worksheet)
Ch 1 - 23 Hots Questions on Chemical Reactions You Must Know!
Ch 1 - Chemical Reactions and Equations (Summary Notes)
Ch 1 - Chemical Reaction (Assertion Type Reasoning Quiz)

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