Metal M, with two electrons in its valence shell (M shell), reacts with oxygen. Class 9

Metal M, with two electrons in its valence shell (M shell), reacts with oxygen. Class 9

Question 1.

Metal M, with two electrons in its valence shell (M shell), reacts with oxygen to form a compound that is slightly soluble in water. Predict its: Class 9

(i) formula

(ii) type of bond

(iii) electrical conductivity of its aqueous solution.

Answer:

The metal M has two electrons in its valence shell (M shell, which is the third shell). This means M has electronic configuration 2, 8, 2. This is magnesium (Mg), which forms Mg²⁺ by losing 2 electrons.

(i) Formula: Mg²⁺ combines with O^2- (oxide ion, valency 2).

Formula: MgO (magnesium oxide)

(ii) Type of bond: Since magnesium (a metal) loses electrons and oxygen (a non-metal) gains electrons, an ionic bond is formed. Type of bond: Ionic bond

(iii) Electrical conductivity of its aqueous solution: MgO is slightly soluble in water and forms an aqueous solution. In this solution, Mg²⁺ and O^2- (or OH ) ions are present and are free to move. Therefore, its aqueous solution will conduct electricity.

Question 2.

Find the molecular mass of nitric acid (HNO₃). Class 9

Atomic mass — H = 1 u; N = 14 u; O = 16 u.

Answer:

HNO₃ contains: 1 hydrogen atom, 1 nitrogen atom, 3 oxygen atoms.

Molecular mass of HNO₃

= (1 u × 1) + (14 u × 1) + (16 u × 3)

= 1 + 14 + 48 = 63 u