|MadSci Network: Chemistry|
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:
Or, since you asked for atoms, and each water molecule is composed of three atoms:
Try the links in the MadSci Library for more information on Chemistry.