A Brief Demonstration about Moles - A chemistry Concept and A Part of Syllabus for Cambridge International Examination O Levels Checkpoint.

1. Chemistry - Moles
A Demonstration to describe the
concept of moles more briefly.

2. Part 1: Chemical
Quantities

3. Introduction
● How did you determine the number of M&Ms in
the bag without actually counting?

4. Atoms
● Can you determine
the number of atoms
of an element even
though you can not
actually count them?
● Yes… IF there is a
conversion factor that
allows you to convert
between mass and
number of atoms.

5. Moles
● The SI base unit that
measures amount of
substance
● Avogadro’s Number:
6.02 x 1023
atoms

6. Moles and Atomic Mass
● The atomic mass of an element
in grams contains one mole of
atoms (Avogadro’s number of
atoms)
● Example: There are 6.02 x
1023
(or 1.0 moles) of atoms in
12.011 g of carbon

7. Moles as Conversion Factors
● Use moles/grams (or grams/moles) as a
conversion factor
● Ex: 16.0 g oxygen
-----------------------------
1 mole oxygen

8. Example 1
● How many moles of helium atoms are in
6.8 grams?

9. Example 2
● How many grams is equal to 1.51 moles of
iron?

10. Examples 3, 4, and 5
● 17.6 grams of chlorine is equal to how
many moles?
● How many moles of nickel do you have if
you have 65.1 g?
● React 1.9 moles of sodium with chlorine
gas to get sodium chloride. How many
grams of sodium do you need?

11. Calculating Molar Mass
● Atomic Mass of an element = “molar mass”
● Molar mass of a compound must be
calculated

12. Calculating Molar Mass
● How many oxygens are in a
DOZEN water molecules?
● How many hydrogens?

13. Calculating Molar Mass
● One mole of WATER
MOLECULES (H2
O)
is one mole of oxygen
atoms and two moles
of hydrogen atoms
● Calculate the mass of
one mole of water
molecules

14. Calculate the molar mass of…
● Boron Trifluoride
● Sodium Iodide
● Sodium Bicarbonate (NaHCO3
)
● Glucose (C6
H12
O6
)
● Copper (III) Sulfate

15. REMEMBER!
● Molar mass is the mass of one mole of an
element/compound.
● Molar mass has units of grams/mole.
● Molar mass can be used as a conversion
factor to find grams or find moles.

16. What you should know so far:
●Explain the concept of a “mole” and give a definition
●Explain how one mole of an element is related to atomic mass
●Find the molar mass of an element (using correct units)
●Determine the number of grams/moles of a given element using
molar mass
●Calculate the molar mass of a compound
●Determine the number of grams/moles of a given compound
using molar mass

17. Making A Solution
● You want to make a solution
by dissolving 4.00 moles of
potassium nitrate in water.
How many grams of the
compound will you need?

18. Example!
● Calculate the number
of moles in a 13.8-g
sample of butane
lighter fluid. The
formula for butane is
C4
H10
.

19. Find the mass of:
●0.702 mol Be.
●2.40 mol N2
.
●0.160 mol H2
O2
.
●5.08 mol NaNO3
.
Find the number
of moles.
●187 g Al
●0.264 g
Li2
HPO4
●333 g SnF2

20. ● How many grams are in 5.66 mol of
CaCO3
?

21. ● How many moles are in 508 grams of
ethanol, CH3
CH2
OH?

22. Part 2: Moles of a
Gas

23. Gases
● Solids/liquids are packed
tightly together and more
space is needed if
atoms/molecules are larger
● Atoms/molecules in gases
are far apart, so larger
atoms/molecules do not
need more space

24. Mole-Volume Relationship
● Avogadro’s Hypothesis –
equal volumes of gases
contain equal numbers of
particles
● 1 mole of any gas takes up
the same volume as long
as…

25. STP
● …as long as the gases
are at the same
pressures and
temperatures
● STP, or “standard
temperature and
pressure” means 0o
C
and 1 atmosphere, which
is air pressure at sea
level

26. Calculating Moles of a Gas
● At STP, a mole of any gas
takes up 22.4 liters.
● Use 22.4 L
/mol
as a
conversion factor!

27. Example 1
● How many liters will a
0.19-mole sample of
oxygen gas take up?

28. Example 2
● A blimp has a volume of 95 kL (95,000 L). If it is
filled with helium at STP, how many moles of the
gas are contained within the blimp?

29. Examples 3 and 4
● Find the number of moles in a
sample of chlorine gas stored
in a 14.2-liter tank at STP.
● What is the volume
of 0.18 moles of
xenon at STP?

30. During Last Week’s Episode…
● Look up molar mass of elements /
calculate molar mass of compounds
● Convert moles-grams using molar mass
as the conversion factor (elements and
compounds)
● Convert moles-liters of a gas using molar
volume (22.4 L/mol)

31. MOLES
Mass (g)
Volume (L) # Atoms
Conversion Factor:
molar mass
Conversion Factor:
molar volume
(22.4 L / 1 mol)
Conversion Factor:
Avogadro’s number
6.02 x 1023
atoms/mol

32. Challenge Problem
● Calculate the mass of
16.4 L of chlorine gas
at STP.

33. Part 3: Molarity

34. Molarity
Molarity is a measure of how
concentrated a solution is
Amount of solute per volume of
solution
High concentration / high
molarity

35. Molarity
Measured in units of moles/liter
mol/L = “M”
A 2.5 M solution has 2.5 moles of salt in one liter of
water

36. Molarity Problems
To make one liter of a
2.5 molar solution of
sodium chloride, how
many grams of sodium
chloride do you need?

37. Molarity Problems
SET MOLARITY
PROBLEMS UP AS A
PROPORTION!
●How many moles of
silver nitrate (AgNO3
)
are in 0.4 L of a 6.0 M
solution?
●How many grams of
silver nitrate is that?

38. Molarity Problem #3
How many grams of lead(IV) chloride must
be dissolved in 50 mL of water to make a
0.1 M solution?
Remember: 0.1 M = 0.1 mol/L

39. Molarity Problem #4
●If you dissolve 56 g of sugar (sucrose,
C12
H22
O11
) into a liter of water, what is the
molarity of the solution you created?

40. Part 3: Percent
Composition
Section 10.3, page 305

41. ● Methane, CH4
, is made of solely hydrogen and
carbon. What percent of the compound is
hydrogen? What percent is carbon?

42. Percent Composition
● Remember that some atoms are
larger, by mass, than others
● Mass of each atom must be taken
into account when calculating
percent composition

43. Percent Composition
● Percent composition = % (by mass) of
each atom in a compound
mass of element
% composition = --------------------------- x 100%
mass of compound

44. Example 1
● 15.1 grams of oxygen combine with 1.9 g
of hydrogen to make water. Find the
percent composition of each element.

45. Example 2
● A sample of glucose is synthesized from
58.00 g carbon, 9.73 g hydrogen, and
77.27 g oxygen. Find the percent
composition for each element.

46. Percent Composition and
Chemical Formulas
● Allows you to find the %
composition of an element
in a compound without
knowing the mass of that
element
molar mass of element
% composition = --------------------------------------- x 100%
molar mass of compound

47. Example 1
● What percentage of a sample of table salt,
sodium chloride, is sodium?

48. Example 2
● Determine the percent composition of iron
(III) oxide.

49. Example 3
● Hypochlorous acid is one of the active
sanitizers in pool-cleaning products. Its
formula is HClO. What percent of the
compound is oxygen?

50. Using Percent Composition
to Calculate Mass
● To calculate mass of one
element in a specific mass
of a compound, multiply
the mass of the compound
by the percent composition
of that element.

51. Using Percent Composition
to Calculate Mass
● Example:
● Carbon is 27.3% of
CO2
. Of 45.1 g of
CO2
, what mass is
carbon?
27.3% x 45.1 g = 12.3 g

52. Example 1
● Find the number of grams of sodium in
10.1 g of sodium sulfate.
● HINT! First write the formula for sodium sulfate,
then find the % sodium.

53. Thank You
A Presentation by Irfad Imtiaz

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