CHAPTER 1-BASIC CONCEPTS

v LAW OF CONSERVATION OF MASS

In all physical and chemical changes, total mass remains same.

v LAW OF CONSTANT PROPORTION

A chemical compound is always found to be made up of same elements combined together in fixed ratio by weight.

v LAW OF MULTIPLE PROPORTION

When two elements combine with each other to form two or more compounds the mass of one of the elements that combine with a fixed weight of other bear a simple whole number ratio to one another.

v GAY LUSSAC’S LAW

When gases react with each other they do so in volumes which bear simple whole number ratio to one another and to the volume of products at STP.

v MOLE CONCEPT

-1 mole=6.022 X 10²³ particles=1 GAM=22.4L=1 gram atom

-molecular mass=2 X vapour density

This is very helpful in doing stotiometric problems.

v EMPRICAL FORMULA

It refers to the simplest ratio of the elements of a compound.

Example

Let us find out the empirical formula and molecular formula for the given condition.

Carbon C=75%

Hydrogen H=25%

It is easy to do if you can remember the following table.

Element	percentage	n =%/atomic mass	Ratio of moles of atom	Simplest ratio
carbon	75	75/12=6.25	6.25/6.25=1	1
hydrogen	25	25/1=25	25/6.25=4	4

Therefore the empirical formula is CH₄

Molecular formula=Empirical formula X n

n=molecular mass/empirical formula mass

Here, both MF and EF are same.

v LIMITING REAGENT

The reagent which is present in smaller amount and reacts completely.

v CONCENTRATION

·         Mole fraction

·         Mass percentage

·         Molarity

                          Number of solute dissolved in 1 liter of solution.

·         Molality

                         Number of solute dissolved per 1 kg of the solvent.