Test: Mole Concept - Class 9 MCQ

Copper atom(s) = 1
Sulfur atom(s) = 1
Oxygen atoms = 4 + 5 = 9
Hydrogen atoms = 10

Total atoms = 1 + 1 + 9 + 10 = 21

∴ There are total 21 atoms in CuSO₄·5H₂O (also called blue vitriol).

C =  12 g = 1 mole 
1 mole = 24 g = n atoms
1 g = (n  * 12) / 24 
 1 g  =  n /2

Avogadro’s number, number of units in one mole of any substance (defined as its molecular weightin grams), equal to 6.022140857 × 10²³.

Water (H₂O) is made from 2 atoms of hydrogen and 1 atom of oxygen. A mole of water molecules would be 2 moles of hydrogen atoms plus 1 mole of oxygen atoms.

Phosphorus exists as a tetratomic molecule i.e.  P₄ molecule. Thus, 1 mole of P₄ = 4 × 6.022 × 10²³ atoms

14 g of nitrogen = gram atomic mass of nitrogen = 1 mole of nitrogen atoms

24 g of magnesium = gram atomic mass of magnesium = 1 mole of magnesium atoms

So, mole ratio = 1:1

Avogadro's number,N_A,is defined as the number of atoms in 12 gram of carbon-12 atoms in their ground state at rest.

By definition it is related to the atomic mass constant  m_{u  b}y the relation.

Avogadro's number are defined in terms of the atomic mass constant (one twelfth of the mass of a 12C atom).

Avogadro's constant and number have by definition the same numerical value. In practice the two terms are used interchangeably.

Given Data:
Mass of Water = ?
no. of moles = 0.5
Molar mass of H₂O = 2(1) + 16 = 18 g/mol

Formula to be Used:
No. of moles = Given Mass/Molar mass

Solution:
No. of moles = Mass of Water/Molar mass
0.5 = Mass of Water/18
Mass of Water = 0.5*18
Mass of Water = 9g

no of moles = mass in gram / molecular mass

no. of moles = 52/4 =13

A sulphate ion (SO₄^2-) contains one sulphur atom and four oxygen atoms. Therefore there are 5 atoms in a sulphate ion. In the ammonium ion (NH₄⁺) there is one nitrogen atom and four hydrogen atoms. So, this ion also contains 5 atoms. 

Atomic mass of hydrogen = 1 a.m.u.

Atomic mass of Sulphur = 32 a.m.u.

Thus, the molecular mass of hydrogen sulphide, which contains two atoms of hydrogen and one atom of sulphur is = 2 × 1 + 1 × 32 = 34 a.m.u.

Mass of 6.022 X 10 ²³ atoms (1 mole) of sodium = 23 g

Number of moles of Ca :- 
n = Given mass in grams / molar mass
=   16 / 40 
=   0.4 mole.

- The mole allows scientists to calculate the number of elementary entities (usually atoms or molecules) in a certain mass of a given substance.

- Avogadro’s number is an absolute number: there are 6.022x10^23 elementary entities in 1 mole. This can also be written as 6.022x10^23 mol-1.

- The mass of one mole of a substance is equal to that substance’s molecular weight. For example, the mean molecular weight of water is 18.015 atomic mass units (amu), so one mole of water weight 18.015 grams.