Question

What mass of H2O contains the same number of molecules as 0.20 g of benzene? A. 0.20 g B. 0.02 g C. 0.01 g

Please explain

Answer 1

mass of benzene = 0.20g

moles of benzene = mass/ molar mass

= 0.20 /78 mol

As 1 mole of any substance has Avogadro number(6.022x10²³ ) of particles

number of molecules in 0.20g of benzene = moles x avogadro number

= (0.20/78)x(6.022x10²³ )

Now we need the mass of water that has this many molecules.

As we have alredy learnt

number of molecules = (mass/molar mass) x Avogardo number

= (mass/ 18) (6.022x10²³ ) of water

Equating number of molecules of wter and benzene we have

(0.20/78)x(6.022x10²³ ) of benzene = (mass/ 18) (6.022x10²³ ) of water

Thus mass of water = 0.20 x 18 /78

=0.0461 g

The option is NONE OF THE GIVEN OPTIONS