# Question d0c80

Apr 1, 2015

The thimble contains $3.3 \cdot {10}^{- 4}$ moles of water.

To go from number of molecules to moles and vice versa, you can use Avogadro's number, which describes the number of atoms or molecules present in a mole of substance.

According to this, each mole contains exactly $6.022 \cdot {10}^{23}$ atoms or molecules; in your case, 1 mole of water would contain $6.022 \cdot {10}^{23}$ molecules of water.

Since $2.0 \cdot {10}^{20}$ is a smaller number than $6.022 \cdot {10}^{23}$, you'll have less than 1 mole of water in a thimble.

The exact value is

2.0 * 10^(20)cancel("molecules") * "1 mole"/(6.022 * 10^(23)cancel("molecules")) = 3.321* 10^(-4)"moles"#

Rounded to two sig figs, the answer will be

$\textcolor{g r e e n}{3.3 \cdot {10}^{- 4} \text{moles of water}}$

Apr 1, 2015

The thimble contains $3.3 \times {10}^{- 4}$ moles of water.

$1 \text{mole water molecules" = 6.022xx10^23 "water molecules}$

$2.0 \times {10}^{20} \cancel{\text{water molecules")xx(1 "mole water molecules")/(6.022xx10^23 cancel ("water molecules}}$ = $3.3 \times {10}^{- 4} \text{moles water molecules}$