1.8 g of ethane gas is used to boil 200 cm' of water. What
is the number of molecules
of the ethane gas?
[Relative atomic mass of
C = 12 and H = 1, Avogadro
constant = 6.02 x 10^23 mol ]

3.6 x 10²²molecules

Explanation:

Given parameters:

Mass of ethane gas  = 1.8g

Unknown:

number of molecules of ethane gas = ?

Solution:

To solve this problem, we first find the number of moles of ethane gas.

  Molar mass of ethane, C₂H₆  = 2(12) + 6(1) = 30g/mol

 Number of moles  =

Insert the parameters and solve;

  Number of moles  =   = 0.06mole

 1 mole of a substance contains 6.02 x 10²³ molecules

 0.06mole of ethane will contain 0.06 x 6.02 x 10²³  = 3.6 x 10²²molecules