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Atoms And Molecules

Question
CBSEENSC9005061
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Define the term:Gram molecular mass. How is it related to the mole and Avogadro number?

Solution

The molecular mass of a substance (compound) expressed in grams is called its gram molecular mass. Ionic compounds do not contain molecules (they consist of ions) and therefore, molecular masses of ionic compounds are equal to their formula masses.
A gram molecular mass of a compound is equal to the mass of 6.023 x 1023 molecules or 1 mole of the substance.
Examples;
(i) A gram molecular mass of hydrogen molecules (molecular mass = 2)
weighs 2 grams and contains 6.023 x 1023 hydrogen molecules.
1 space gram space molecular space mass space of space hydrogen space space space equals space 2 space grams space equals stack space 6.023 space cross times space 10 to the power of 23 with Avogadro space number below space equals space space space space 1 space mole space of stack space straight H subscript 2 with Hydrogen space molecule below space space space space space space space space space space space

(ii) A gram molecular mass of sodium chloride (molecular or formula mass = 58.5) weighs 58.5 grams and contains 6.023 x 1023 sodium chloride units.

Some More Questions From Atoms And Molecules Chapter

When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen ? Which law of chemical combination will govern your answer?

What are polyatomic ions? Give examples.

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.

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