IX Model Test Questions Chemistry Test # 3 for Chapter # 1 (Fundamental of Chemistry)

 

Answer

Atomic Mass Unit (amu)

One twelfth (1/12) of the mass of one atom of carbon-12 is termed as Atomic Mass Unit abbreviated as a.m.u. i.e.                                                           1 a.m.u. = 1/2^th weight of carbon-12 = 1.66 x 10^–24 g

Molecular Mass

It is the average mass of a molecule of a substance (element or compound) as compared with 1/12^th mass of one atom of C-12. molecular Formula mass or Molecular Mass of a substance is the sum of atomic masses of all atoms present in a molecule of a substance shown by its molecular formula. 

 

Formula Mass

Formula mass of a substance (ionic compounds) is the sum of atomic masses of all atoms in formula unit shown by its simplest or empirical formula.

 

Gram Atomic Mass

The atomic mass of an element expressed in gram is called gram atomic mass. It is also called 1 mole.

 

Gram Molecular Mass

The molecular mass of an element or a compound expressed in gram is called gram molecular mass. It is also called 1 mole.

 

Gram Formula Mass

The formula mass of an ionic compound expressed in grams is called gram formula mass. It is also called 1 mole.

 

Molar Mass

The relative atomic mass or molecular mass or formula mass of a substance expressed in gram is called its molar mass. The unit of molar mass is gram/mol.

 

Mole

Mole is the S.I. base unit of chemical amount of substance. A mole of a substance can be defined as the atomic mass or molecular mass or formula mass of a substance (element or compound) expressed in gram containing 6.02 x 10²³ particles (Atoms, molecules or ions)”.

 

Avogadro’s number

The number of elementary particles (atoms, molecules, ions or formula units) contained in one mole  of a substance (element or compound) is found to be 6.02 x 10²³ called Avogadro’s number. It is denoted as N_A.

 

Molar Gas Volume or Molar Volume (V_M)

According to Avogadro, one gram mole of any gas at STP occupies volume of 22.4 dm³ (where standard temperature is O^OC and standard pressure is 1 atm). The volume occupied by one mole of any gas at s.t.p is 22.4 dm³ (Litre) and is referred to as Molar Volume. 

                                1 mole of a gas  at S.T.P = 22.4 dm³ mol^-1

Difference between Atomic and Molecular Mass

Difference between Gram atom and Gram Molecule

Difference between Molecular and Formula Mass

Difference between Empirical and Molecular Formula 

Q20. Calculate the formula mass (a.m.u) of the following

Al₂O₃ , MgCl₂ , NaCl , KNO₃, washing soda (Na₂CO₃.10H₂O)

Solution

Q21. Calculate molecular (a.m.u) of the following

C₂H₅OH (ethanol) , H₂O (water), NH₃(ammonia) , CO₂ (carbon dioxide) , acetic acid (CH₃COOH) , nitric acid (HNO₃) and benzene (C₆H₆) 

Solution

Q7. Calculate number of mole in 53 g of Na₂CO₃ and 36 g of water. 

Solution

Calculation of number of moles in 53 g of Na₂CO₃

Given mass of Na₂CO₃ (ionic compound) = 50 g

Molar mass of Na₂CO₃ (ionic compound) = 2 x23 + 1 x 12 + 3 x 16 = 106 g/mol

No. of moles of Na₂CO₃  = ?

No. of moles (n) = mass of substance in gram/molar mass of substance

                                = 53/106 = 0.5 mole

 

Calculation of number of moles in 36 g of H₂O

Given mass of H₂O (Molecular compound) = 36 g

Molar mass of H₂O  = 2 x1 + 1 x 16 = 18 g/mol

No. of moles of H₂O  = ?

No. of moles (n) = mass of substance in gram/molar mass of substance

                                = 36/18 = 2.0 mole

Q8. Calculate the mass of 1 atom of carbon and 1 molecule of water.

Solution

Calculation of Mass of 1 atom of carbon

Calculation of Mass of 1 molecule of water 

Q9. Calculate the number of atoms present in 2.3 g of sodium (Na)

Solution

Q10. A coin of silver (Ag) having 8.5 g weight. Calculate the number of moles and number of atoms of silver in coin?

Solution

 

Calculation of number of moles in 8.5 g of silver

Given mass of silver = 8.5 g

Molar mass of silver = 108 g/mol

 

No. of moles (n) = mass of substance in gram/molar mass of substance

                                = 8.5/108 = 0.0787 mole

Calculation of number of atoms in 8.5 g of silver

Number of atoms = number of moles x Avogadro’s number

Number of atoms = 0.0787 x 6.02 x 10²³

Number of atoms = 0.473 x 10²³ = 4.73 x 10²² atoms

Q11. Calculate number of mole in 900 g of glucose.

Solution

Calculation of number of moles in 900 g of glucose

Given mass of C₆H₁₂O₆  = 900 g

Molar mass of C₆H₁₂O₆ = 6 x 12 + 12 x 1 + 6 x 16 = 180 g/mol

No. of moles (n) = mass of substance in gram/molar mass of substance

                                = 900/180 = 5 mole

Q12. Calculate the number of moles, number of molecules present in 8g of C₆H₁₂O₆?

Solution

Calculation of number of moles in 8 g of glucose

Given mass of C₆H₁₂O₆  = 8 g

Molar mass of C₆H₁₂O₆  = 6 x 12 + 12 x 1 + 6 x 16 = 180 g/mol

No. of moles (n) = mass of substance in gram/molar mass of substance

                                = 8/180 = 0.04 mole

 

Calculation of number of molecules in 8 g of glucose

No. of particles = no. of moles x Avogadro’s number

                      = 0.04 x 6.02 x 10²³ = 2.67 x x 10²²

Q11. How many liters of carbon dioxide would be produced if 0.450 of a mole of carbon monoxide reacts with excess oxygen at STP. (answer;10.08 liter of Co₂)

2CO_(g) + O_2(g) ®2CO_2(g)

Solution

Q8.        Calculate the number of moles, number of molecules and number of atoms present in 10 g  H₂SO₄?

Solution

Given

Mass of H₂SO₄ = 10 g

Molar mass of H₂SO₄ =  2(1) + 32 + 4(16) = 98 g/mol

Avogadro’s number = 6.02 x 10²³

Atomicity of H₂SO₄ = 2+1+4 =7

 

Required

No. of moles = ?

No. of molecules = ?

No. of atoms = ?

 

Calculating No. of Moles of H₂SO₄

No. of moles (n) = mass of substance/molar mass = 10/98 = 0.1 mol

 

Calculating No. of Molecules of H₂SO₄

No. of moles (n) = no. of particles/Avogadro’s no (N_A)

No. of particles (molecules) = n x N_A = 0.1 x 6.02 x 10²³ = 6.02 x 10²² Molecules

 

Calculating No. of atoms of H₂SO₄

No. of atoms = no. of molecules x atomicity = 6.02 x 10²² x 7 = 4.214 x 10²³ atoms