CHEMISTRY (Part-V) (Railway)

Carbon contains four electrons in its outer shell.

• Hence, it has unique property due to which it forms covalent bonds with other carbon atoms.

• This property is called "catenation or self- linking".

A pH of 11.6 means that the soil is alkaline.

• Aluminium sulphate (Al₂(SO₄)₃) can be used to treat alkaline soil.

• It is extremely acidic, so it is added to very alkaline soils to balance the pH for plants.

Neutralisation is the reaction of an acid and a base. which forms water and a salt.

An acid is a substance or compound that releases hydrogen ions (H⁺) when in solution. A base is a substance that releases hydroxyl ions (OH⁻) when in solution.

The reaction of these two ions to give the neutral molecule water (H⁺ + OH⁻ → H₂O)

A thermal decomposition reaction happens when one reactant gets broken down by heating.

• When zinc carbonate is heated, it will decompose to produce zinc oxide, which is the metal oxide, and carbon dioxide gas. ZnCO₃ → ZnO + CO₂

• From this equation it is visible that the ZnCO₃ is breaking into two smaller molecules which are ZnO and CO₂.

Hence the reaction is a thermal decomposition reaction.

Chlor-alkali process is the one in which an electricity is passed through an aqueous solution of Sodium chloride or brine (NaCl) which decomposes to form sodium hydroxide (NaOH).

• 2NaCl(aq)+2H₂O(l)→ 2NaOH(aq)+Cl₂(g)+H₂(g)

• Sodium hydroxide is used for making artificial textile fibers. It is also used in the manufacture of paper.

Homologous series is defined as a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain.

• This series will be differing with a successive member of CH₂.

• As the molecular mass increases in any homologous series, a gradation in physical properties is seen. This is because the melting points and boiling points increase with increasing molecular mass.

In a chemical equation, the subscript (aq) after a molecule means that it is aqueous.

• An aqueous solution is a solution in which the solvent is water.

• For example:

Na(s)+H₂O(l)→H₂(g)+NaOH(aq).

This shows that NaOH formed is dissolved in water.

The elements which have two electrons in the outermost orbit are called alkaline earth. metals.
• Alkaline metals make up the group 2 of the modern periodic table.
• For example, Magnesium, Calcium, and Strontium have two electrons in their outermost orbit.

In pure water, the concentrations of the hydronium ion (H₂O⁺) and the hydroxide ion (OH⁻) are equal, and the solution is therefore neutral.

• Because of its highly polar structure, liquid water can act as either an acid (by donating a proton to a base) or a base (by using a lone pair of electrons to accept a proton).

• So, adding water to hydroxide ion increases its concentration.

Sulphuric acid and lithium hydroxide neutralise each other and produce lithium sulfate and water.

• H₂SO₄(aq) + 2LIOH(aq) → Li₂SO₄(aq) + 2H₂O(aq)

• This reaction is a type of double replacement (double displacement) reaction that is also a neutralizsation reaction.