Ex1. An atom has atomic number Z = 6 and mass number A = 12. Establish:

a. what element it is;

b. how many protons, neutrons and electrons it has.

Ex2. Calculates the molar mass of hydrogen peroxide, H, 0, barium fluoride, Baf, and carbon dioxide, CO,.

Ex1.

a) Carbon : atomic number Z = 6 and mass number A = 12

b) Protons = 6; electrons = 6; neutrons = 6.

Ex2.

Molar mass of H₂O₂ = 34 g; BaF = 156 g; CO = 28 g.

Explanation:

Ex1.

a) the element with atomic number 6 and mass number 12 is carbon

b) number of protons and electrons in a element is given by its atomic number; and for neutrons its mass number - atomic number (A-Z).

⇒ protons = Z = 6; electrons = Z = 6.; neutrons = A-Z = 12-6 = 6.

Ex2.

Molecular formula of hydrogen peroxide is given by H₂O₂.

⇒ molar mass = 2*mass of hydrogen + 2*mass of oxygen

⇒ molar mass = 2*1 + 2*16 = 34. g

molar mass of BaF = mass of barium + mass of fluoride.

= 137 + 19 = 156 g

molar mass of CO = mass of carbon + mass of oxygen

= 12 + 16 = 28 g