Question

How many moles of water, are in 13.81 g of water?

Answer 1

To answer this, we wil need to use the molar mass of Water, M.

Let m be the mass of water and n be the number of moles of water, then:

`\begin{gathered} M_{H_(2)O}=\frac{m_(H_2O)}{n_{H_(2)O}} \\ n_{H_(2)O}=\frac{m_(H_2O)}{M_{H_(2)O}} \end{gathered}`

To calculate the molar mass of water, we need the molar mass of H and O, which we can get on a periodic table:

`M_(H_2O)=2\cdot m_H+1\cdot m_O=(2\cdot1.00794+1\cdot15.9994)g\/mol=18.01528g\/mol`

So:

`n_(H_2O)=\frac{m_(H_2O)}{M_{H_(2)O}}=(13.81g)/(18.01528g\/mol)=0.76657\ldots mol\approx0.7666mol`

So, there are approximately 0.7666 mol of water.