CHEMISTRY (Part-V) (Railway)

Metal oxides are compounds that contain only two elements, one is a metal and another one is an oxygen atom. Exmaple: Magnesium oxide.

• They are basic in nature because when they react with dilute acids then, salt and water are formed as the products. Example: MgO + 2HCl → MgCl₂ + H₂O

• Moreover, the oxides turn moist red litmus paper blue and blue remains blue.

In 1866, John Newlands, an English scientist, arranged the then-known elements in the order of increasing atomic masses.

• He started with the element having the lowest atomic mass (hydrogen) and ended at thorium which was the 56th element.

Phenolphthalein shows pink colour with bases.

• Magnesium reacts with hot water to form magnesium hydroxide and hydrogen. Mg + 2H₂O → Mg(OH)₂ + H₂ Being basic in nature, Magnesium hydroxideturns phenolphthalein solution pink.

Valence electrons are the total number of electrons present in the outermost shell of an element.

With an atomic number of 9. Fluorine (F) has the electronle configuration of 1s²2s²2p⁵. Thus, the number of valence electrons present in the fluorine is 7.

Aluminium (Al) with atomic number of 13 has 3 valence electrons.

The number of valence electrons in Hydrogen (atomic number of 1) is 1 and nitrogen (atomic number 7) has 5 valence electrons.

A valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond.

• The number of valence electrons in Fluorine is 7: Oxygen: 6; Carbon: 4; Lithium: 1.
• So, in terms of valence shell electrons, F > O > C > Li

Baking powder is a fine white powder, which is used as a leavening agent in cooking.

• It is used to increase the volume and lighten the texture of baked goods.

• It works by releasing carbon dioxide gas into a batter or dough through an acid-base reaction, causing bubbles in the wet mixture to expand and thus leavening the mixture.

A series of compounds with the same general formula is called a homologous series.

• One such series is the alkenes: C₂H₄ (ethene); C₃H₆ (propene), and C₄H₈ (butene) are the first three members of the series. The members of the series differ from the next by CH₂.

• So, the fourth next member of the homologous series of the compound Propene will be Heptene (C₇H₁₄).

Neutral → Solution D → PH is 7

Strongly alkaline → solution C→ PH is 11

Strongly acedice → Solution B → PH is 1

weakly acidic → Solution A → PH is 4

Weakly alkaline → Solution E → PH is 9

We can arrange the PH in creasing order of hydrogen ion concentration as: 11 < 9 < 7 < 4 < 1

C < E < D < A < B

Magnesium hydroxide reacts with Hydrochloric acid to form Magnesium Chloride and water.

• It is a neutralisation reaction since a base (Magnesium hydroxide) reacts with an acid (Hydrochloric acid) to form a salt (Magnesium Chloride).

The atomic number of Carbon is 6 with an electro- nic configuration of 1s², 2s², 2p².

• Hence, carbon has 4 electrons in its valence shell. Carbon can lose or gain 4 electrons in order to gain stability.

• Carbon cannot form C⁴⁺ because if it loses 4 electrons, it will require a large amount of energy to remove 4 electrons, leaving behind a carbon cation with six protons in its nucleus holding on to just 2 electrons.

• Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements.