NCERT Solutions For Class 7 Science Chapter 9

NCERT Solutions Class 7 Science Soil

The NCERT solutions class 7 Science chapter 9 Soil is crucial for the students of 7th standard. The NCERT solutions for class 7 Science chapter 9 Soil is provided here to help students understand the chapter in an easy and interesting way. These NCERT Solutions for class 7 Science chapter 9 is created by subject experts according to the latest CBSE syllabus. Students must practice the solutions regularly to prepare effectively for their examination. Check the NCERT Solutions for class 7 Science chapter 9 pdf given below.

Q1. Identify the following processes :

  1. Beating aluminum to make foil
  2. Digestion of food
  3. Melting of wax   
  4. Burning of coal
  5. Photosynthesis
  6. Sugar dissolving in water

Ans.

1)physical change          2) chemical change        3)physical change        4)chemical change 5)chemical change         6)physical change

 

Q2.classify the following into true or false:

  1. cutting wood into pieces is a chemical change.
  2. Manure formation from leaves is a chemical change.
  3. Rust and iron are same material.
  4. Iron pieces coated with zinc do not get rusted easily.
  5. steam condensation is not a chemical change.

Ans. :

  1. False
  2. True
  3. False
  4. True
  5. True

 

Q3. Complete the following:

  1.  Lime water turns milky when carbon dioxide is passed through it as __________ is formed in it.
  2. ____  is the chemical name of baking soda.
  3. ____ and ____ are the two methods which can prevent rusting of iron.
  4. Physical changes are the changes in which only _____ properties of the substance change.
  5. _____ are the changes in which new substances are formed.

Ans.:

  1.  calcium carbonate
  2.  Sodium hydrogen carbonate
  3.  galvanization, painting or greasing
  4.  Physical
  5.  Chemical

 

Q4. When lime juice is mixed with baking soda, with the evolution of a gas, bubbles are formed. Identify what type of change.

Ans.

Lemon juice   +   baking soda                      ———>       co2(bubbles)  +   other substances

(citric acid)         ( sodium hydrogen-carbonate )                (carbon dioxide)

It is a chemical change

 

Q5. Both physical and chemical change take place when a candle burns. Identify these changes. Give another familiar example in which both physical and chemical change take place.

Ans.

Both physical and chemical change occurs when a candle burns.

  1. Physical change: Melting of wax, vaporization of melted wax.
  2. Chemical change: Carbon Dioxide, heat and light formed due to the burning of vapours of wax.

LPG is another example in which a chemical change occurs when the gas burns in air and physical change occurs when LPG comes out of the cylinder and is converted from liquid to gaseous state.

 

Q6. Is formation of curd a chemical process?

Ans.

Formation of change is a chemical change because we cannot get back the original substance, i.e. milk, and a new substance is formed with other chemical properties like taste and smell.

 

Q7. Why burning of wood and cutting it into smaller pieces are considered as different types of changes? Explain.

Ans.

Burning of wood is a chemical change because new substances are formed in burning. Wood + Oxygen ——-> Charcoal + Carbon Dioxide + Heat + Light

Whereas cutting wood into small pieces is a physical change because we can only reduce the size of the wood and no new substance is formed.

 

Q8. How is the copper sulphate crystal formed?

Ans.

 Add few drops of dilute sulphuric acid in a beaker containing water. Heat the water, add copper sulphate powder when it starts boiling. Continue to add copper sulphate till no more powder can be dissolved. Continuously stir the solution during this process. Filter the solution and leave it for cooling. Crystals of copper sulphate will be formed after cooling.

 

Q9. How rusting is prevented when it is painted?

Ans.

Painting prevents iron from coming in contact with oxygen and moisture. Without the presence of oxygen and moisture rusting cannot take place. Thus painting of iron prevents rusting.

 

Q10. Why rusting is quicker in coastal areas? Explain.

Ans.

In coastal areas, moisture content in the air is higher. So rusting is faster in coastal areas.

 

11.Choose the correct one.

In kitchen we use LPG gas. In cylinder it exists as a liquid.

It becomes a gas when it comes out of the cylinder (change 1).

Then it burns (change 2).

The following statement pertain to these changes.

a)change-1 is a chemical change.

b)change-2 is a chemical change.

c)Both 1 and 2 are chemical changes.

d)none of these is a chemical change.

Ans.

b)change-2 is a chemical change.

 

Q12. Choose the correct one.

Animal wastes are decomposed by anaerobic bacteria and produce biogas(change 1).

The biogas which is a fuel is burnt.(change 2).

The following statements pertain to these changes.

(a) Change-1 is a chemical change.

(b)Change-2 is a chemical change.

(c)Both 1 and 2 are chemical changes.

(d)None of these is a chemical change.

Ans.

c)Both 1 and 2 are chemical changes.