The mole

The mole is a common unit used to represent the quantity of a chemical substance and is the amount of that substance that contains 6.2023×1023 particles (Avogadro’s constant).
Number of moles =mass of substance/R.F.M

Calculating masses

Na2SiO3

R.F.M= (R.A.M Sodium x 2) + (R.A.M Silicon) + (R.A.M Oxygen x 2)
R.F.M= (23×2) + 28+ (16×3) = 36+12+48 =96

Al2S3

R.F.M= (27×2) + (32×3) = 54+96=150

Percentage composition

Calculate the percentage of carbon in sodium carbonate

Percentage = (R.A.M) /R.F.M × 100

Na2CO3

R.F.M of Na2CO3 = (23×2) +12+ (16×3) =106

Percentage of C =(12/106) x 100= 11.32%

Percentage of O = (R.A.M × 3(number of oxygen’s))/R.F.M = (48/106) x100 = 45.28%

Please note that 1 mole of a substance = R.F.M in grams of a substance

Moles Example

Calculate the number of moles of sodium chloride in 58.5g.

Number of moles = mass of substance/R.F.M = 58.5g/ 58.5 = 1

Calculate the mass of 0.12moles of sodium

1 mole of Na = 23g

0.12 mole of Na=? g

Mass of substance = R.F.M × number of moles = 23 x0.12 = 2.76g Na

1 mole of any substance contains 6.023×1023 molecules, atoms or ions.

Example 1; 1 mole of Sodium Chloride contains 6.023×1023 ions.

Example 2; 1 mole of CH4 contains 6.023×1023 molecules.

Example 3; 1 mole of Li contains 6.023×1023 atoms.

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