Ans. Number of moles in 5g of calcium = mass / molar mass
= (5 / 40) = 0.125 Number of moles in 2g of oxygen = mass / molar mass
= (2 / 16) = 0.125
Now we will calculate the simplest ratio of the element by dividing the number of moles of each element by the smallest value. Since number of moles of each element is 0.125, therefore calcium and oxygen are present in a ratio of 1 : 1. Thus the empirical formula of the compound is CaO.
For calculating the molecular formula, we need the molecular mass of the compound. However, because a compound with the formula CaO is known,
Therefore the molecular formula of the compound is CaO.
Q. (i) Name the body which approves the nomenclature of elements and compounds.
(ii) The symbol of sodium is written as Na and not as S. Give reason.
(iii) Name one element which form diatomic and one which form tetra atomic molecules. [CBSE 2011 ]
Ans. (i) IUPAC (International Union of Pure and Applied Chemistry)
(ii) Latin name of sodium is Natrium. The first two letters (Na) of this name represents the symbol of sodium.
(iii) Oxygen forms diatomic molecules and phosphorus forms tetra atomic molecules.
Q.Calcium and Oxygen are combined in the rates of 5:4 by mass to form calcium oxide. What mass of Oxygen gas would be required to react with 2.5 g of calcium ?
Ans: Calcium and oxygen combine in the rates of 5:4 by mass to form calcium oxide
let x gram of oxygen is required to react with 2.5 g of calcium to form calcium oxide
Therefore 5/4 = 2.5 / x
5 x = 2.5 * 4
x = (2.5 *4 ) / 5
x = 2
Therefore 2 grams of oxygen is required to react with 2.5 grams of calcium to form calcium oxide .