Question

Calculate the amount of moles in 1.17 x 1016 molecules of H2S.

Answer 1

`\boxed {\boxed {\sf About \ 1.94 *10^(-8) \ mol \ H_2S}}`

Step-by-step explanation:

To convert from molecules to moles, Avogadro's Number must be used.

• 6.022* 10²³

This number tells us how many particles (atoms, ions, molecules, etc.) are in 1 mole of a substance. For this problem, it is moles of hydrogen sulfide.

• 6.022*10²³ molecules of hydrogen sulfide in 1 mole.

We can use the number as a fraction.

`\frac { 6.022 *10^(23) \ molecules \ H_2S}{1 \ mol \ H_2S}`

Multiply by the given number of molecules.

`1.17*10^(16) \ molecules \ H_2S *\frac { 6.022 *10^(23) \ molecules \ H_2S}{1 \ mol \ H_2S}`

Flip the fraction so the molecules of hydrogen sulfide will cancel out.

`1.17*10^(16) \ molecules \ H_2S *\frac {1 \ mol \ H_2S }{ 6.022 *10^(23) \ molecules \ H_2S}`

`1.17*10^(16) *\frac {1 \ mol \ H_2S }{ 6.022 *10^(23) }`

`\frac {1.17*10^(16) \ mol \ H_2S }{ 6.022 *10^(23) }`

`1.94287612*10^(-8) \ mol \ H_2S`

The original measurement of molecules had 3 significant figures so we must round our answer to that.

For the number we calculated, that is the hundredth place. The 2 in the thousandth place tells us to leave the 4 in the hundredth place.

`1.94 *10^(-8) \ mol \ H_2S`

There are about 1.94*10⁻⁸ molecules of hydrogen sulfide.