The mole is the base unit of amount of
substance. One mole of substance has 6 x 10^{23 }particles.
Particles may be molecules, atoms, ions and electrons.

**Number
of particles**

One mole of substance contains 6 x
10^{23 }particles.
This value is called Avogadro’s number.

Number of particles in 1 mol of substance = 6 x 10^{23}

Number of particles in 2 mol of substance = 2 x 6 x 10^{23}

Number of particles in y mol of substance = y x (6 x 10^{23})

Hence,

**Number of particles = number of moles x (6 x 10**^{23})

^{23})

**Volume of gas at r.t.p**

One
mole of any gas occupies 24 dm^{3
}(24 000 cm^{3})
at room temperature and pressure. This volume is called the molar volume of a
gas.

At r.t.p,

Volume
occupied by 1 mol of gas = 24 dm^{3
}Volume occupied by 2 mol
of gas = (2 x 24) dm^{3
}Volume occupied by y mol
of gas = (y x 24) dm^{3
}

Hence,

**Volume of gas = number of moles x 24 dm**^{3}

^{3}

**Mass of substance in g**

Molar mass is the mass of one mole of a substance.

Take for example, copper metal

Mass of 1 mol of copper metal = 64 g (64 gmol^{-1})

Note: 64 gmol^{-1 }is the molar mass of copper metal. This value is obtained from The Periodic Table

Mass of 2 mol of copper metal = (2 x 64) g

Mass of y mol of copper metal = (y x 64) g

Hence,

**mass of substance = number of moles x molar mass**

**Concentration of aqueous solution**

The concentration of a solution is the amount of solute dissolved in a unit volume of a solution.

Concentration
of a solution can be expressed in gdm^{-3
}or moldm^{-3}_{.}

When concentration is expressed in moldm^{-3}, it is called the molar concentration.

Concentration of aqueous solution in gdm^{-3} can be calculated by multiplying concentration in moldm^{-3} with the molar mass of the solute