MadSci Network: Chemistry

Re: How many atoms are in a single drop of water?

Date: Tue Oct 10 10:40:53 2000
Posted By: Michael Onken, Admin, MadSci Network
Area of science: Chemistry
ID: 971146792.Ch

This is a similar calculation to # of molecules in salt, but with different numbers. First, a drop of water is between 45 and 50 microliters (Ál), if dispensed from a dropper; I will use 50 Ál for the calculation. 50 Ál of water should have a mass of 50 milligrams (mg) at Standard Temperature and Pressure. Water is H2O, which has a molecular mass of 18.015 g/mole, so 50 mg of water contains 2.775 millimoles (mM). According to Avogadro's number, one mole of any compound contains 6.022 x 1023 molecules, so 2.775 mM of water has 1.67 x 1021 H2O molecules. In American notation that means:

There are 1.67 sextillion molecules of H2O in a drop of water.

Or, since you asked for atoms, and each water molecule is composed of three atoms:

There are about 5 sextillion atoms in a drop of water.

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