Name: _________________
Date: ___________________
Avogadro’s Constant and the Mole
LEARNING GOAL: Today I am learning how to determine the number of particles in a
sample of matter.
Recall
Avogadro’s Constant
o Symbol NA
o One mole (1 mol) of a substance contains 6.022 x 1023 particles
o i.e. NA = 6.022 x 1023 particles/mol
The Mole
o Symbol mol (n)
o The SI unit for the amount of substance that contains as many
elementary particles (atoms, molecules, ions, or formula units) as exactly
12 g of carbon-12
o Used for convenience by chemists because atoms are so small. Without
the mole, chemists would have to deal with very large numbers
Converting Number of Particles to Moles
Ex.1) A vat of cleaning solution contains 4.05 x 1025 molecules of ammonia, NH3. How
many moles of ammonia are in the vat?
Converting Moles to Number of Particles
Ex. 2) A sample contains 3.15 x 10-3 mol of platinum, Pt. How many atoms of platinum
are in the sample?
Ex. 3) A sample contains 4.0 mol of C6H12O6.
a) How many molecules are there?
b) How many atoms of carbon are in the sample?
a)
b)
Name: _________________
Date: ___________________
Avogadro’s Constant and the Mole
Practice Questions
1. A small pin contains 0.0178 mol of iron. How many atoms of iron are
in the pin?
2. A sample contains 4.70 x 10-4 mol of gold. How many atoms of gold
are in the sample?
3. How many formula units are contained in 0.21 mol of magnesium
nitrate?
4. A litre of water contains 55.6 mol of water. How many molecules of
water are in the sample?
5. Consider a 0.829 mol sample of sodium sulfate.
a. How many formula units are in the sample?
b. How many sodium ions are in the sample?
6. A sample of bauxite ore contains 7.71 x 1024 molecules of aluminum
oxide. How many moles of aluminum oxide are in the sample?
7. A sample of hydrogen cyanide contains 3.33 x 1022 atoms. How
many moles of hydrogen cyanide are in the sample? Hint: Find the
number of molecules of hydrogen cyanide first.
8. A sample of pure acetic acid, CH3COOH, contains 1.40 x 1023 carbon
atoms. How many moles of acetic acid are in the sample?
Answers:
1. 1.07 x 1022
2. 2.83 x 1020,
3. 1.3 x 1023,
4. 3.35 x 1025,
5a. 4.99 x 1023, 5b. 9.98 x 1023,
6. 12.8 mol,
7. 1.84 x 10-2 mol,
8. 1.16 x 10-1 mol