Avogadro’s Constant

6.02 x 10^23 atoms = 12 grams

The mole is used in measurements in a way similar to the use of “dozens”.

  • The reason why we use moles in chemistry is because of the vast number of molecules and atoms involved in the calculations
  • Just like it’s easier to manage the thought of 2 dozen eggs instead of 24, scientists prefer to think of a reaction requiring 2 moles of carbon rather than 1,204,428,200,000,000,000,000,000 particles
  • The number is huge and unimaginable, a bit like the number of stars in the galaxy
  • Using the mole unit helps simplify calculations

Note: the symbol for mole is “mol”

The mole concept

The mole

The mole concept

The mole concept

Avogadro's constant and the mole

The mole is equal to 602 thousand billion billion!

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Sublimation is the process of turning from solid to vapor without going through the intermediate liquid phase.

Sublimation of Ice

We are all familiar with ice melting before it evaporates. However, in sublimation, the liquid phase is omitted. In order for a solid to sublime, it must exhibit a higher than usual vapor pressure and weak intermolecular attractions.… Read the rest

Atmospheric Pressure & Boiling Point

What is vapor pressure chemistry cartoon

What is vapor pressure?

Water always evaporates no matter what the temperature or atmospheric pressure is.

Even in the coldest of winter, snow and ice can evaporate by a process called sublimation. They can turn straight into vapor (the gaseous stage) without melting.

The vapor that escaped into the air whether by evaporation or sublimation had sufficient energy to break away from the intermolecular forces of the water.… Read the rest


Molality = mol solute / kg solvent

Molality is defined as the number of moles of solute per 1 (kg) of solvent.

  • Solute = particles you dissolve
  • Solvent = the liquid you use for dissolving the particles

Molality (m) = mol solute / kg solvent


Calculate molality (m) of 29.8 g of glucose (C6H12O6) dissolved in 622.8 g of water

Symbol Element Atomic weight Atoms
C Carbon 12.01 6
H Hydrogen 1.008 12
O Oxygen 16.00 6

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Colligative Properties of Solutions

Colligative properties of solutions

The characteristics of a solution such as the boiling point, freezing point and vapor pressure are known as colligative properties. Colligative properties apply only to solutions and not gases or solids.


The word colligative comes from the same Latin root that the word collection comes from.… Read the rest