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Atoms And Molecules
Question
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Give an account of existence of various elements and compounds.

Answer

Metals exist as atomic crystals and do not form molecules. Generally, metals and other elements like carbon and silicon do not have single molecular structure but consist of a very large indefinite number of atoms bonded together. A form of carbon bonded with sixty atoms is called buckminsterfullerence.

Non-metals exist as molecules containing one or more atoms. For example, argon exists as Ar and nitrogen as N2.

Compounds containing non-metals only exist as molecules. For example, compound of nitrogen and hydrogen is a ammonia molecule. Compound of carbon and oxygen is a carbon dioxide molecule.

Compounds containing metal and non-metal exist as ions. For example, compound of sodium and chlorine consists of positively charged sodium ions and negatively charged chloride ions.

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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.