Question

What amount (moles) is represented by each of these samples?
a. 20.0 mg caffeine, c8h10n4o2
b. 2.72 1021 mo?

Answer 1

Answer:

                  a)  Moles of Caffeine  =  1.0 × 10⁻⁴ mol

                  b) Moles of Ethanol   =  4.5 × 10⁻³ mol

Solution:

Data Given:

                  Mass of Caffeine  =  20 mg  =  0.02 g

                  M.Mass of Caffeine  =  194.19 g.mol⁻¹

                  Molecules of Ethanol  =  2.72 × 10²¹

Calculate Moles of Caffeine as,

                               Moles  =  Mass ÷ M.Mass

Putting values,

                               Moles  =  0.02 g ÷ 194.19 g.mol⁻¹

                                Moles  =  1.0 × 10⁻⁴ mol

Calculate Moles of Ethanol as,

                                                         As we know one mole of any substance contains 6.022 × 10²³ particles (atoms, ions, molecules or formula units). This number is also called as Avogadro's Number.

The relation between Moles, Number of Particles and Avogadro's Number is given as,

                          Number of Moles  =  Number of Molecules ÷ 6.022 × 10²³

Putting values,

                          Number of Moles  =  2.72 × 10²¹ Molecules ÷ 6.022 × 10²³

                          Number of Moles  =  4.5 × 10⁻³ Moles