How many molecules of water are present in 7.9 g of water

The number of molecules = 2.6408 molecules

Explanation:

To determine the number of molecules in water, we need to determine how many moles of water we have

Water has a molar mass of 18.015g/mol, this means that one mole of water molecules has a mass of 18.015g

To find the number of molecules,

7.9g * 1 mole H2O / 18.015g

= 0.4385mole of H2O

Using avogadro number,

0.4385 H2O * 6.022 * 10^23molecules / 1 mole of H2O

That's 0.4385 H2O multipled by 6.022*10^ 23 molecules divided by 1 mole of H2O

Which gives = = 2.6408 molecules