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

1 Answer
Sep 10, 2017

Answer:

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.