Quantitative Chemistry

The mole concept applies to all kinds of particles: atoms, molecules, ions, electrons, formula units, and so on. The amount of substance is measured in moles (mol). The approximate value of Avogadro’s constant (L), 6.02 × 10^23mol^–1, should be known.

n = m / Mr

n = N (number of particles) / 6.02 X 10^23

CHEMICAL FORMULA is the number of each type of atom in the smallest viable unit of the substance.

EMPIRICAL FORMULA is the simplest possible ratio of elements in a substance.

Example - 2.476g of an oxide of copper is found to contain 2.199g of copper. What is its empirical formula?

1. Divide each mass by its Mr to find the moles

Oxygen - 0.277 / 16.00 = 0.01731mol

Copper - 2.199 / 63.55 = 0.03460mol

2. Divide by the smallest number to find the ratio

1:1.999 therefore, 1:2

Cu^2O

Example 2 - Find the molecular formula of CH^2O which has the molecular mas of 60.

Divide the molecular mass with the relative molecular mass:

60/2 = 30.0

Therefore, the molecular mass is twice the empirical formula.

CH^2O -> C^2 H^4 O^2

The balancing numbers are known as the coefficients of the reaction.

Use of the balancing number is essential to fulfill the law of conservation of matter.

The stoichiometry is the overall set of balancing coefficients of a chemical reaction.

THEORETICAL YIELD = n x M

Experimental Yield = m / Theoretical yield x 100

For RTP - n = v / 24,000 cm^3

For STP - n = v / 22,400 cm^3

c = n/v