# How many molecules are present in a 0.05*cm^3 volume of LIQUID water under standard conditions?

Sep 10, 2017

Approx. $1.67 \times {10}^{21}$ individual water molecules......pretty vast but not infinite.....

#### Explanation:

We approach all these problems dimensionally. We want the answer as a dimensionless number, and our calculation should give us a dimensionless number if we do the correct product/quotient....

${\rho}_{\text{density"="mass"/"volume}}$, and thus $\text{mass"=rhoxx"volume}$

And number of moles $=$ $\text{mass"/"molar mass}$....

And so we take ....................

$\frac{1.0 \cdot g \cdot c {m}^{-} 3 \times 0.05 \cdot c {m}^{3}}{18.01 \cdot g \cdot m o {l}^{-} 1} = 2.78 \times {10}^{-} 3 \cdot m o l$...

And we multiply this molar quantity by $\text{Avocado number}$ to get....

2.78xx10^-3*molxxN_A-=2.78xx10^-3*molxx6.022xx10^23*mol^-1=??

And note that this approach gives us a dimensionless number as required.