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Atoms And Molecules
Question
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When you stand on loose sand, your feet go deep into the sand. Now, lie down on the sand. You will find that your body will not go deep in the sand. Give reason for the difference in the two cases.

Answer

The force exerted on the sand is equal to the weight of our body in both the cases. 

When we stand on loose sand, our weight acts on a smaller area of the sand. Hence, a large pressure (= force/area) is exerted onto sand and our feet penetrate deeper into the sand.

When we lie down, our weight acts on a larger surface area of the sand. Hence, a smaller pressure is exerted onto sand and our feet stay on the ground only. 

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Some More Questions From Atoms And Molecules Chapter

Write the chemical formulae of the following:

(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate 
(d) Aluminium chloride
(e) Calcium carbonate

Give the names of the elements in the following compounds.

(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder 
(d) Potassium sulphate.

Calculate the molar mass of the following substances:

(a) Ethylene
(b) Sulphur molecule, S8
(c) Phosphorus molecule, P4
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO3.

What is the mass of:

(a) 1 mole of nitrogen atoms

(b) 4 moles of aluminium atoms

(c) 10 moles of sodium sulphite.

Convert into mole

(a) 12 gm of oxygen gas

(b) 20 gm of water

(c) 22 gm of carbon dioxide.

What is the mass of?

(a) 0.2 mole oxygen atoms.

(b) 0.5 mole of water molecules.

Calculate the number of molecules of sulphur (S8) present in 16 gm of solid sulphur.

Calculate the number of aluminium ions present in 0.56 gm of aluminium oxide.

Explain law of conservation of mass.

50 g of 10% lead nitrate is mixed with 50 g of 10% sodium chloride in a closed vessel. After the reaction has taken place, it was found that 6.83 g of lead chloride was precipitated. Besides, the reaction mixture contained 90 g water and sodium nitrate. Calculate the amount of sodium nitrate formed.