• Moles and moletown
• Molarity
• Moles Worksheet The mole (abbreviated "mol") is an essential unit of measurement in chemistry. The mole measures how many atoms, molecules, or ions are present within a given sample. Using Avogadro's number, one mole is always 6.02 x 10^23 units. The exact unit depends on what the problem asks, so it might be molecules, atoms, or something else. Moletown, pictured above, is a simple way to transition between moles, grams (mass), liters (volume), and number of particles.

The following information is organized in the moletown model:

• Moles to mass: multiply by molar mass (the mass present on the periodic table for an atom, or the sum of the atoms’ masses in a molecule)
• Mass to moles: divide by the molar mass
• Moles to volume: (at STP: 0 degrees Celsius and 1 atmosphere pressure) multiply by 22.4
• Volume to moles: divide by 22.4
• Moles to number of particles: multiply by 6.02 x 10^23
• Number of particles to moles: divide by 6.02 x 10^23

The factor label method of conversions can also be used. Knowing the conversions from moletown, such as

6.02 x 10^23 particles/mole, 22.4 liters/mole, or molar mass (grams)/mole, factors can be multiplied to cancel out certain units and leave the desired units behind. See the answer key to the worksheet below for more information.

Note that at conditions other than STP, gas molecules become more or less compact and therefore take up a volume different than 22.4 liters/mol. The equation PV=nRT (where temperature is in Kelvin and the units of the constant R match the units of pressure) can be used to solve for a missing variable.

## Molarity

Molarity is a way to measure concentration. Concentration is the number of moles of an atom, ion, or molecule within a given volume.

The formula to calculate molarity is: M=m/L or Molarity=moles/liters

This equation can easily be used to solve for any of the variables, not just molarity, as long as the other two variables are given or can be computed with other information from the question.

## Practice Worksheet

Moles practice and answer key (pdf)