Molar Mass
7 Minutes
Molar mass explained for students, showing how to calculate moles and particle counts in sand and salt. A chemistry lesson in English.
- What a mole is and finding molar mass from the periodic table
- Calculating moles and molecules in 100 grams of sand
- Finding the mass of a salt packet from its molecule count
What this lesson teaches
Molar mass is the mass of one mole of a substance, which contains 6.02 times 10 to the power of 23 particles like atoms or molecules. It acts as a bridge that connects the visible mass of an object to the count of tiny, invisible particles inside it.
The mole and molar mass
- Particles in chemistry refer to atoms and molecules that cannot be seen with the human eye.
- One mole contains 6.02 times 10 to the power of 23 particles, which is called Avogadro's number.
- The molar mass of an element is found by taking its number from the periodic table and writing it in grams.
- A mole acts as a bridge between the large mass we can weigh and the tiny particles inside.
Finding molecules in a sample of sand
Silicon dioxide is the chemical name for sand, made of one silicon atom and two oxygen atoms. The periodic table gives silicon as 28.05 grams and oxygen as 15.99 grams. Multiplying oxygen by two gives 31.98 grams, and adding silicon gives a molar mass of 60.03 grams for one mole of sand. Dividing a 100-gram sample of sand by 60.03 gives 1.66 moles, and multiplying by Avogadro's number reveals 9.99 times 10 to the power of 23 molecules in that sample.
Finding salt packet mass from molecule count
A salt packet contains 10.3 times 10 to the power of 24 sodium chloride molecules. Dividing this count by Avogadro's number of 6.02 times 10 to the power of 23 gives 17.1 moles of salt. The periodic table gives sodium as 22.98 grams and chlorine as 35.45 grams, which add together to make a molar mass of 58.43 grams for one mole of sodium chloride. Multiplying 17.1 moles by 58.43 grams gives 999 grams, which shows the packet weighs approximately one kilogram.
Converting between mass and particles
- Divide the mass of a substance by its molar mass to calculate how many moles it contains.
- Multiply the number of moles by 6.02 times 10 to the power of 23 to get the total number of particles.
- Divide a known number of particles by Avogadro's number to find the number of moles.
- Multiply the number of moles by the molar mass to find the total mass of the substance.