Relative Atomic Mass and Relative Molecular Mass

 

1. The relative atomic mass of an element is defines as the average mass of one atom of that element compare with 1/12 of the mass of the carbon -12 atom

 

Relative atomic mass = average mass of one atom of the element

                               1/12 of the mass of a carbon-12 atom

 

 

2. The relative molecular mass of a substance is defines as the average mass of a molecule of the substance compared with 1/12 of the mass of a carbon – 12 atom

 

Relative molecular mass = average mass of one molecular of a substance

                               1/12 of the mass of a carbon-12 atom

3. The relative formula mass is used instead if relative molecular mass when ionic compound are involved.

 

 

The Number of Moles and the Number of Particles

 

1. 1 mole of any substance contains 6.02 x 10²³ particles
2. 6.02 x 10²³ is known as Avogadro constant

 

 

The Number of moles and the Mass of substance

 

1. 1 mole of a substance has a mass equal to its relative atomic ( molecular or formula) mass expressed in gram
2. The mass of one mole of any substance is called its molar mass

 

 

The number of moles and the volume of gas

 

1. 1 mole of any gas occupies a volume of 22.4 dm³ at STP and 24 dm³ at room temperature and pressure
2. The molar gas volume is the volume that is occupied by 1 mole of any gas.

 

Number of mole of a substance =        mass of the substance

                                                       Molar mass of the substance

 

Number of mole of a substance =  Number of particles

                                                         Avogadro constant

 

Number of mole of any gas =   Volume of the gas

                                                  Molar gas volume

 

Chemical Formulae

 

1. The chemical formula which shows the simplest whole number ration of the atoms of each element present in a compound is called its empirical formula
2. The chemical formula which  shows the actual number of atoms of each element in molecule is called its molecular  formula
3. The empirical formula of some metallic oxide can be determined experimentally through the combustion reaction of the metals in oxygen gas or air or through the reduction reaction of their oxides by hydrogen gas.

 

Chemical Equation

 

1. A chemical equation is a useful and fast way to summaries what has happened in a chemical reaction
2. In a qualitative interpretation, the chemical equation shows 3 important facts about a chemical reaction; the reactant, the products and the physical state of the reactants and product.
3. In quantitative interpretation, the coefficients of each formula in a balanced chemical equation tell us the molar ratio or the number of atoms of reactant and product involved in chemical reaction
4. The relation ship between the amount (usually in mole) of reactant and product involved is known as the stoichiometry of the reaction

 

EXERCISE

 

1.  
1. Using an example, explain the term empirical formula and molecular formula of a compound
2. Lead metal form two oxide with formula PbO or PbO₂. You are required to carry out an experiment to determine the empirical formula of a sample of lead oxide. Describe the procedure of the experiment and show the calculation involved in determining the empirical formula (O,16;Pb,207)