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

1 Answer
anor277
Sep 10, 2017

Approx. 1.67xx10^21 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_"density"="mass"/"volume", and thus "mass"=rhoxx"volume"

And number of moles = "mass"/"molar mass"....

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

(1.0*g*cm^-3xx0.05*cm^3)/(18.01*g*mol^-1)=2.78xx10^-3*mol...

And we multiply this molar quantity by "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.

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