Question

calculate the number of moles and molecules present in 0.032 mg of Methane if carbon is equal to 2 and hydrogen is equal to 1

Answer 1

we first get its molar mass by adding the masses of C and H. There are C atoms and 4 H atom:

CH4 = 12 + 4*1 = 16 g/mol

Then we divide the given mass by the molar mass:

0.032 mg = 0.000032 g

0.000032 g / (16 g/mol)

= 0.000002 mol or 2 x 10^(-6) mol

To get the molecules present, recall that 1 mole of a substance is equal to 6.022 x 10^23 particles / mol (Avogadro's number). We'll multiply this to the the moles:

6.022 x 10^23 / mol * 2 x 10^(-6) mol

= 1.2044 x 10^18 molecules of CH4

Answer 2

moles = mass / molar mass

mass methane = 0.032 mg = 3.2x10^-5 g

moles methane = 3.2x10^-5 g / 16.042 g/mol
= 1.994x10^-6 moles methane
= 2.0x10^-6 moles

1 mole of anything is 6.022x10^23 units of that anything.
So 1 mole metane has 6.022x10^23 molecules of methane.

Thus molecules of methane = moles x 6.022x10^23 molecules / mol
= 1.994x10^-6 mol x 6.022x10^23 molecules/mol
= 1.2x10^18 molecules

this is your answer