Question

How many moles are in 4.3 x 1024 molecules of H20?

Answer 1

`\boxed {\boxed {\sf About 7.1 \ mol \ H_2O}}`

Step-by-step explanation:

To convert from molecules to moles, we must use Avogadro's Number: 6.022*10²³. This tells us the amount of particles (atoms, molecules, etc.) in 1 mole of a substance. In this case, the particles are molecules of water.

`\frac {6.022*10^(23) \ molecules \ H_2O} {1 \ mol \ H_2O}`

Multiply by the given number of molecules.

`4.3 *10^(24) \ molecules \ H_2O *\frac {6.022*10^(23) \ molecules \ H_2O} {1 \ mol \ H_2O}`

Flip the fraction so the molecules of water cancel.

`4.3 *10^(24) \ molecules \ H_2O *\frac {1 \ mol \ H_2O} {6.022*10^(23) \ molecules \ H_2O}`

`4.3 *10^(24) *\frac {1 \ mol \ H_2O} {6.022*10^(23) }`

`\frac {4.3 *10^(24)\ mol \ H_2O} {6.022*10^(23) }`

`7.140484889 \ mol \ H_2O`

The original measurement of atoms has 2 significant figures ( 4 and 3), so our answer must have the same. For the moles we calculated, that is the tenth place. The 4 in the hundredth place tells us to leave the 1.

`7.1 \ mol \ H_2O`

There are about 7.1 moles of water.