How many h20 molecules in a drop of water

Eggs, doughnuts, and many other things are sold by the dozen—a unit of twelve items. Smaller objects, such as pencils, may be ordered in units of , that is, by the gross, and paper is packaged in reams, each of which contains sheets. A stack of paper containing a mole of sheets would extend more than a million times the distance from the earth to the sun, and 6.

A student may contain 10 27 water molecules about 10 4 mol , and would need to accumulate about 10 18 ten million million million, but only 0. The proof is given soon in Using the Molar Mass of Water. Obviously there are a great many particles in a mole of anything. Why have chemists chosen such an unusual number as 6. Surely some nice round number would be easier to remember. The rest of it is a simple chemistry calculation. Let's use the volume of a water drop that is used by the medical and scientific community.

The accepted average volume of a drop of water is exactly 0. It turns out there are over 1. To calculate the number of molecules and atoms in a water drop, you need to know the chemical formula of water. There are two atoms of hydrogen and one atom of oxygen in each water molecule, making the formula H 2 O.

So, each molecule of water contains 3 atoms. Determine the molar mass of water. Do this by adding up the mass of hydrogen atoms and oxygen atoms in a mole of water by looking up the atomic mass of hydrogen and oxygen on the periodic table. The mass of hydrogen is 1. In other words, one mole of water has a mass of Use the density of water to determine the mass of water per unit volume. The density of water actually varies depending on conditions cold water is denser; warm water is less dense , but the value typically used in calculations is 1.

In other words, 1 milliliter of water has a mass of 1 gram. A drop of water is 0. One mole of water is Finally, use Avogadro's number to determine the number of molecules in a drop of water.

Avogadro's number tells us there are 6. So, next we calculate how many molecules there are in a drop of water, which we determined contains 0. Put another way, there are 1.

Now, the number of atoms in a droplet of water is 3x the number of molecules:. Or, there are about 5 sextillion atoms in a drop of water. One interesting question is whether there are more atoms in a drop of water than there are drops of water in the ocean. To determine the answer, we need the volume of water in the oceans. There are over 1. Defining the volume of a drop of water is the first part of the problem.

Water droplets vary dramatically in size. The medical and scientific community commonly define the average volume of a drop of water as exactly 0. This is a good starting point for calculating molecules and atoms in a drop of water. Use the chemical formula of water to determine the mass of a single molecule. The formula of water is H 2 O, which means there are two hydrogen atoms and one oxygen atom in each water molecule. Each water molecules contains a total of 3 atoms. Find the molar mass of water.