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:

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

So, there are approximately 0.7666 mol of water.