How many moles are there

Search for:. Converting between Mass and Number of Moles. Learning Objective Convert between the mass and the number of moles, and the number of atoms, in a given sample of compound.

To convert between mass and number of moles, you can use the molar mass of the substance. Show Sources Boundless vets and curates high-quality, openly licensed content from around the Internet. Licenses and Attributions. We count in moles.

What is cool about choosing the number we did for moles - all our 1 mole amounts match the molecular weight of the molecule in grams. It is a unit factor that we use for converting from grams to moles and moles to grams.

That equality or equivalency is:. Let's do an example with water. Water has the chemical formula of H 2 O. So how many moles of water are in a glass of water? Well we need to be specific about the "glass" of water. Well, the general consensus on a glass of water is 8 fl oz fluid ounces. Let's do the conversion now:. In general, if you know the mass of a substance and the number of mole, you can calculate the molecular weight MWt :.

Rearrange that equation algebraically to get moles from MWt and mass, or mass from MWt and moles. Atomic Weights are Scaled for Mole Counting Take a look at the periodic table and look at those decimal numbers - the atomic weights.

You can use this information to calculate the number of moles in a sample of a compound with a known weight or mass. Conversely, if you know the number of moles of the compound you have, you can calculate the weight or mass of the sample. These calculations apply whether the compound is a solid, liquid or gas, but to perform either of them, you need to know the molecular mass of the compound.

As long as you know the chemical formula of the compound, you can look up its molecular mass. To find the number of moles of a compound you have on hand, look up the molecular weight of the compound and divide that number into the weight you have on hand.

If you know the number of moles, you can find the weight by multiplying the number of moles by the molecular weight. In chemistry, you often see the words mass and weight used interchangeably.

Although weight is a measure of the force of gravity on an object while mass is the amount of matter it contains, the two quantities are essentially equivalent, as long as as all measurements are performed in Earth's gravitational field. If you perform experiments in space though, the distinction becomes important.

In the metric system, the units for mass and weight are the same: gram and kilogram. Every compound is a collection of atoms, and each atom has a characteristic weight. It's displayed under the atoms symbol in the periodic table. For example, the atomic weight of hydrogen is 1.