Basic concepts of Chemistry and chemical calculations

Atomic mass unit

One twelfth of the mass of a Carbon-12 atom in its ground state.

Relative atomic mass (RAM)

Ratio of the average atomic mass to the unified atomic mass unit.

Ar = average mass of the atom/unified atomic mass

Molecular mass

Ratio of mass of a molecule to the unified atomic mass unit.

Mole

• One mole is the amount of substance of a system, which contains as many elementary particles as there are atoms in 12 g of Carbon-12 isotope.

• The elementary particles can be molecules, atoms, ions, electrons or any other specified particles.

Avogadro Number

The total number of entities present in one mole of any substance is equal to 6.022 × 10²³.

Molar mass

• Mass of one mole of a substance

• Molar mass of a compound is equal to the sum of its relative atomic masses of its constituents

• Unit : g mol-¹

Molar volume

Volume occupied by one mole of a substance in the gaseous state at a given temperature and pressure.

Gram equivalent mass

• Mass of an element (compound or ion) that combines or displaces 1.008 g hydrogen, 8 g oxygen or 35.5 g chlorine

• equivalent mass = Molar mass (g mol-¹) / equivalence factor ( eq mol-¹)

Equivalent mass of acids

E = Molar mass of the acid / basicity of the acid

Basicity - No. of replaceable H+ ions

Equivalent mass of Bases

E = Molar mass of the the base / Acidity of the base

Acidity - no. of replaceable OH- ions

Equivalent mass of Oxidising agent or reducing agent

E = Molar mass of the oxidising (or) reducing agent/ No. of moles of electrons gained or lost by one mole of the oxidising or reducing agent

Stoichiometry

It gives the numerical relationship between chemical quantities in a balanced chemical equation

Limiting reagent

• When a reaction is carried out using non-stoichiometric quantities of the reactants, the product yield will be determined by the reactants that is completely consumed

• It limits the further reaction from taking place and is called as the limiting reagent.

Excess reagents

Other reagents which are in excess

Cyanide poisoning

• Oxygen binds to haemoglobin

• Cyanide binds irreversibly to haemoglobin and blocks oxygen binding

• Transport of oxygen from lungs to tissues is stopped

• Leads to quick death of the person

Oxidation number

• Imaginary charge left on the atom when all the other atoms of the compound have been removed in their usual oxidation states

Oxidation number of elements in ground state

0

Oxidation number of Na+

+1

Oxidation number of Cl-

-1

Oxidation number of Hydrogen

+1 except metallic hydrides (-1)

Oxidation number of Fluorine

-1

Oxidation number of alkali metals (1st group)

Li, Na, K, Rb, Cs

+1

Oxidation number of alkaline earth metals (2nd group elements)

Mg, Ca, Sr

+2

Sum of the oxidation numbers of elements in a compound

0

Sum of the oxidation numbers of elements in a polyatomic ion

Charge carried by the ion

Oxidation reaction

• Addition of Oxygen

• Removal of Hydrogen

• Loss of electrons

• Oxidation number in increases

• Eg : C + O2 → CO2

Reduction reaction

• Addition of Hydrogen

• Removal of Oxygen

• Gain of electrons

• Oxidation number decreases

• Eg : H2 + Cl2 → 2 HCl

Combination reactions

It is a reaction in which two substances combine to form a single compound

C + O2 → CO2

Decomposition reaction

It is a reaction in which a compound breaks down into two or more components

2 KClO3 → 2 KCl + 3 O2

Disproportionation reaction (Auto redox reaction)

It is a reaction in which same compound undergoes both oxidation and reduction

2 H2O2 → 2 H2O + O2

Displacement reaction

It is a reaction in which an ion or atom in a compound is replaced by an ion or atom of another element.