(a) Define: (i) Molecular mass, (ii) Avogadro constant. (b) Calculate the number of molecules in 50 g of CaCO3. (Atomic mass of Ca = 40 u, C = 12 u and O = 16 u) (c) If one mole of sodium atom weighs 23 g, what is the mass (in g) of one atom of sodium ?

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Q. (a) Define 'formula unit' of an ionic compound. What is the formula unit of (i) sodium chloride, and (ii) magnesium chloride ?
(b) Calculate he formula masses of the following compounds :
(i) Calcium chloride
(ii) Sodium carbonate
(Given : Atomic masses : Ca = 40 u ; Cl = 35.5 u ; Na = 23 u ; C = 12 u ; O = 16 u)

Q. (a) Define mole. What are the two things that a mole represents.
(b) What weight of each element is present in 1.5 moles of sodium sulphite, Na₂SO₃?

(Atomic masses : Na = 23 u ; S = 32 u ; O = 16 u)

Q. A sample of a mixture of

C a C l_{2}

and

N a_{2} C O_{3}

weighing

4.22

g was treated to precipitate all the

C a

C a C O_{3}

. This

C a C O_{3}

is heated and quantitatively converted into

0.959

g of

C a O

. Calculate the percentage of

C a C l_{2}

in the mixture.

(Atomic mass of

C a = 40, O = 16, C = 12

and

C l = 35.5 g / m o l e)

The number of atoms in one mole is $6 \times 10^{23}$ . Then the number of sodium ions in 19.5 gm of sodium chloride will be? (If one mole of a substance is equal to gram molecular mass of the substance.)

(a) A gas cylinder contains 24 × 10²⁴ molecules of nitrogen gas. If Avogadro's number is 6 × 10²³ and the relative atomic mass of nitrogen is 14, calculate:
(i) Mass of nitrogen gas in the cylinder.
(ii) Volume of nitrogen at STP in dm³.

(b) Commercial sodium hydroxide weighing 30 g has some sodium chloride in it. The mixture on dissolving in water and subsequent treatment with excess silver nitrate solution formed a precipitate weighing 14.3 g.What is the percentage of sodium chloride in the commercial sample of sodium hydroxide? The equation for the reaction is
NaCl + AgNO₃ → AgCl + NaNO₃.
[Relative molecular mass of NaCl = 58; AgCl = 143]

(c) A certain gas 'X' occupies a volume of 100 cm³ at S.T.P. and weighs 0.5 g. Find its relative molecular mass.

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