Question

Cyclohexane, a commonly used organic solvent, is 85.6% c and 14.4% h by mass with a molar mass of 84.2 g/mol. what is its molecular formula?

Answer 1

The molecular formula of organic solvent is C6H12

calculation

find the empirical formula first as in step 1 and 2

Step 1: find the moles of C and H

• moles = % composition/molar mass

• from periodic table molar mass of C= 12 g/mol while that of H= 1 g/mol
• moles is C is therefore = 85.6/12= 7. 13 moles
• moles of H= 14.4/1 - 14.4 moles

Step 2: calculate the mole fraction by dividing each mole by smallest number of mole(7.13)

• that is C= 7.13/7.13 = 1

H= 14.4/7.13 =2

the empirical formula is therefore = CH2

Then calculate the molecular formula from empirical formula

step 3: divide the grams molar mass by empirical formula mass

empirical formula mass = 12+(1 x2) = 14 g/mol

= 84.2/ 14 = 6

step 4: multiply each of the subscript within the empirical formula with the value gotten in step 3

• that is [CH2]6 = C6H12 therefore the molecular formula = C6H12