How many molecules are there in 39 grams of water?

1 Answer
Nov 16, 2015

Answer:

#"39 g H"_2"O"# contains #1.3xx10^24"molecules H"_2"O"#.

Explanation:

One mole of water has a molar mass of #"18.015 g/mol"# and #6.022xx10^23 "molecules H"_2"O"#. Therefore,

#"1 mol H"_2"O"##=##"18.015 g H"_2"O"##=##6.022xx10^23"molecules H"_2"1O"#

Multiply the given mass of water times the conversion factors that cancel grams and moles of water, leaving molecules of water, as demonstrated below.

#39cancel("g H"_2"O")xx(1cancel("mol H"_2"O"))/(18.015cancel("g H"_2"O"))xx(6.022xx10^23"molecules H"_2"O")/(1cancel("mol H"_2"O"))=1.3xx10^24"molecules H"_2"O"#