Question

How many molecules of ethane ( C2H6) are present in 0.197g of C2H6?

Answer 1

1 mol of any substance is made of 6.022 x 10²³ unita, these units could be atoms making up elements or molecules making up a compound.

1 mol of C₂H₆ is made of 6.022 x 10²³ molecules of C₂H₆

the relative molecular mass of C₂H₆ is - (2 x C) + (6 x H)

atomic mass of C = 12 g/mol , H = 1 g/mol

= (2 x 12 g/mol ) = (6 x 1 g/mol ) = 24 + 6 = 30

therefore relative molecular mass of C₂H₆ is 30 g/mol

1 mol of C₂H₆ has a mass of 30 g

30 g of C₂H₆ is 1 mol

therefore 30 g of C₂H₆ is made of 6.022 x 10²³ molecules of ethane

then 0.197 g of C₂H₆ is made of - 6.022 x 10²³ / 30 x 0.197 = 3.95 x 10²¹ molecules of C₂H₆

answer is 3.95 x 10²¹ molecules of C₂H₆

Answer 2

3.945 x 10²¹ molecules

Step-by-step explanation:

• Firstly, we need to calculate the no. of moles using the relation:

• n = mass/molar mass = (0.197 g)/(30.07 g/mol) = 6.55 x 10⁻³ mol.

• It is known that every 1.0 mol of a molecule contains Avogadro's number of molecules (NA = 6.022 x 10²³).

• ∴ 0.197 g of C₂H₆ will contain = (6.55 x 10⁻³ mol)(6.022 x 10²³) = 3.945 x 10²¹ molecules.