What is the empirical formula of this?

Caffeine $\left({\mathrm{C}}_8{\mathrm{H}}_{10}{\mathrm{N}}_4{\mathrm{O}}_2\right)$ a substance found in tea and coffee.

1. Classical idea of redox reactions:

(i) In chemical classification, the matter is classified as mixtures, compounds and elements.

(ii) Relative atomic mass $=\frac{\text{Average of the}}{\text{atom}}$

(iii) Molecular mass: The relative molecular mass of any compound can be calculated by adding the relative atomic masses of its constituent atoms.

(iv) Stoichiometry is the quantitative relationship between reactants and products in a balanced chemical equation in moles.

(v) Redox reaction is a reaction in which oxidation and reduction reaction occur simultaneously.

(vi) Oxidation: A process involving increase in oxidation number by the loss of electrons.

(vii) Reduction: A process involving decrease in oxidation number by gain of electrons.

(viii) Oxidising Agent: A substance which involves decrease in oxidation number of one or more of its elements.

(ix) Reducing Agent: A substance which involves increase in oxidation number of one or more of its elements.

2. Oxidation Number

Oxidation Number is the charge which an atom has in its ion or appears to have when present in the combined state.

3. Equivalent weight

Equivalent weight of an oxidising/reducing agent is equal to its molecular weight divided by the number of electrons gained/lost as represented in the balanced chemical equation.

4. Types of redox reactions:

(i) Combination redox reactions are those in which either one or both the reacting species are in the elemental state.

(ii) Decomposition redox reactions are those reactions in either one or both the decomposition products are in the elemental state.

(iii) Displacement redox reactions are those in which an atom or ion in a compound is replaced by an atom or ion of some other element

(iv) Disproportionation reactions. A reaction in which the same species is simultaneously oxidised as well as reduced is called a disproportionation reaction.

5. Balancing of redox reactions:

Balancing of redox reactions can be done by oxidation number method or Half reaction method.

6. Mole concept:

(i) Avogadro’s law states that equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules.

${\mathrm{N}}_{\mathrm{A}} = 6·022 \times {10}^{23}$

(ii) $1$ mole $=$ Gram atomic mass if substance is element$=$Gram molecular mass if substance is molecular

(iii) $1$ mole $= 6·022 \times {10}^{23}$ atoms if substance is atomic $= 6·022 \times {10}^{23}$ molecules if substance is molecular

(iv) $1$ mole $= 22·4 \mathrm{L}$ at STP if substance is gaseous.

7. Empirical formula and Molecular formula:

Empirical formula is the formula which expresses the simplest whole number ratio between atoms of various elements present in one molecule of the compound. Molecular formula is the formula which expresses actual number of atoms present in one molecule of the compound.

Molecular formula $= \mathrm{n} \times$ Empirical formula $(\mathrm{n} = 1, 2, 3......)$

$\mathrm{n}=\frac{\text{Molecular}}{\text{Mass}}$

8. limiting reactant:

The reactant which reacts completely in the reaction is called limiting reactant/reagent. The other reactant is called the excess reactant. Limiting reactant decides the amounts of other reactants reacted or the amounts of products formed.