Chemistry (Part-VII) (Railway)

Aqueous solution of sodium chloride is called brine.

• When electricity is passed through brine solution, the following reaction takes place:

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

• Chlorine gas is given out at the anode and hydrogen gas given out at the cathode.

• The hydrogen gas burns a matchstick with a pop sound.

A carbon-carbon bond is a covalent bond between two carbon atoms.

• The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms.

• The single bond is generally a sigma (σ) bond that arises from one hybridized orbital from each C atom.

Metallic character increases from right to left across a period of the periodic table, and from top to bottom down a group.

•The alkali metals in group 1 are the most active metals, and cesium is the last element in the group.

•Thus, it is the element having the most metallic character.

In the reaction, KI + PbNO₃ → 2KNO₃ + PbI₂, the reactants potassium iodide and lead nitrate react to form potassium nitrate and lead iodide.

• It is a double displacement reaction because there is exchange of ions between potassium iodide and lead nitrate.

Ethanol reacts with potassium dichromate (K₂Cr₂O₇) in an acidic medium to form Ethanoic acid.

• C₂H₅OH + K₂Cr₂O₇ → CH₃CHO (acidified) → CH₃COOH

• This reaction is used in detecting the presence of alcohol in breath in suspected drunken drivers.

A chemical reaction in which heat is released along with the formation of products is called an exothermic reaction.

• For example, a lot of heat is produced when carbon burns in oxygen.

• Reactions in which heat is absorbed are known as an endothermic reaction.

• The reaction occurs as follows:
H₂CO₃ + NaOH → Na₂CO₃ + H₂O.

Methane, (CH₄), is a covalent compound with atoms that are linked by covalent bonds.

• It is a nonpolar covalent compound that is formed by sharing of electrons.

• Thus, no ions are present in the compound.

• Methane is a member of Alkane (CₙH₂ₙ₊₂) group.

When dilute hydrochloric acid (HCl) is added to granulated zinc placed in a test tube, zinc metal is converted to zinc chloride and hydrogen gas is evolved in the reaction.

• Zn + HCl → H₂ + ZnCl₂

• The evolved hydrogen gas is colorless and odorless.

Group 11 of the periodic table consists of copper (Cu), silver (Ag), and gold (Au).

• The element Mercury (Hg) lies in Group 12 of the periodic table.