Notes of Chemistry Class 11 Chapter 2 Stoichiometry

The word Stoichiometry is derived from Greek word stoicheion (element) + metron (measure)

1. Comes from Greek word: stoicheion (element) and metron (measure)
2. It is branch of chemistry that deals with relationship between reactants and product produced in a chemical reaction.
3. Means: how much reactant is required to form specific amount of product.
4. Eg: \(\displaystyle \frac{Ca + CO_3}{Reactant} = \frac{CaCO_3}{Product}\)
5. Combination of element to form compound is ruled by 5 laws called as 'Law of stoichiometry'
6. Dalton's atomic theory: (Given By: A teacher John Dalton in the year 1803 to 1808 AD)

📌 Main postulates:

1. All matters are composed of extremely small, indivisible and discrete particles called atoms.
2. Atoms of same element are identical in all properties like mass,shape , size etc, but atoms of different elements are different in properties.
   (Eg: All Atoms of Na is identical to themselves but different from calcium's atoms)
3. Atoms can neither be created nor destroyed by simple chemical reactions.
   (Possible by Nuclear Reaction)

4. Atom of an element takes part in chemical reaction to form molecule.
Eg: \(\mathrm{C} + \mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}\)  \(\mathrm{N}_{2} + \mathrm{H}_{2} \longrightarrow \mathrm{NH}_{3}\)

5. Atoms combine in the ratio of small whole number to form compound.

Click to Watch Video mo

✘ Drawbacks (Modifications Read)

1. Atoms are divisible: Not by simple means but possible to break by Nuclear Reaction.
Atoms can further be divided as \(\mathrm{e}^{-}\), \(\mathrm{p}^{+}\), \(\mathrm{n}^{0}\)

2. Isotopes:

• According to Dalton, atoms of same element are similar in mass or have same mass number.
• But, Isotopes are atoms of same element with different atomic mass.Eg: There are different Atoms of hydrogen which have different masses like protium ,deuterium ,tritium, etc. These all atoms belongs to same element hydrogen but they have different mass number. This shows the failure of Dalton's Atomic theory.
  eg: \(\mathrm{H}^{1}, \mathrm{H}^{2}, \mathrm{H}^{3}\)

3. Isobars:

• According to Dalton, atoms of different elements have different mass.
• But, Isobars are atoms of different element but they have same mass number.
  Eg: Calcium (40)   Argon (40)

✏️ Argon and calcium are different element , according to John Dalton atomic theory, atoms of calcium should not have equal atomic weight with the atoms of Argon, but in reality atoms of Calcium & atoms of Argon have same atomic weight called as Isobars. This also shows weakness Dalton's atomic theory

🧪 Problem (Law of conservation of mass)

10 gm of Calcium (Ca) react with oxygen (O₂) to give 14 g of calcium oxide (CaO). If the law of conservation of mass holds true, what will be the mass of oxygen (O₂) required in this reaction?[Ans: 4g]

Experimental Verification. — By : Landolt's Experiment

⚖️ 2. Law of Constant Composition

(Law of Definite Proportion)

“Proportion (Ratio) of elements of chemical compound always remain same, irrespective of their source”

Eg: Water (From Rain, Sea, Ice or combining H₂ and O₂ they will result H₂O)

\[ \rightarrow H_2O \Rightarrow 2 + 16 \quad \text{(1:8)} \quad \text{Ratio (Always Same)} \] O₂, 2 Atoms of Hydrogen, 1 Atom of Oxygen → 2:1 Ratio of atoms (Always Same)

🧪 Exp. Verification:

→ Heating copper(II) nitrate, copper(II) hydroxide & copper(II) carbonate.

\[ \begin{array}{c} \text{Cu(NO}_3)_2 \xrightarrow{\Delta} \text{CuO} + \text{CO}_2\text{NO}_2 + \text{O}_2 \\ \text{Cu(OH)}_2 \xrightarrow{\Delta} \text{CuO} + \text{H}_2\text{O} \end{array} \]

→ Metallic copper was converted by current of dry H₂ gas.

→ Mass of oxygen = mass of oxide – mass of copper

\[ = \text{CuO} - \text{O2} \quad\text{(note)}\quad = \text{CuO} - \text{Cu} = O2 \] \[ \text{Ratio of Mass of copper \& oxygen = Nearly Equal (4:1)} \]

9. A pure sample of ammonia contains 14g of nitrogen and 3g of hydrogen. A second sample of pure ammonia contains 28g of nitrogen & 6g hydrogen. Which law of chemical combination is illustrated by these data? Justify.

→ Law of Definite Proportion

✦Notes by : SJ Classes YT Channel✦