STOIchioMETRY!
Lesson 2
Molar Concentration
• Remember that concentration is c = n/v
• Stoichiometry is the relationship between the
moles.
• We can rearrange the equation to solve for moles
by
• n = cv
• NOTE – If volume is mentioned, we cannot
ASSUME the volume is 22.4L. We can only use
22.4L if the given information is a GAS and at STP!
Example
• What mass of barium phosphate will result if
139.0mL of 5.000M barium bromide reacts
with sodium phosphate?
• 3BaBr2 + 2Na3PO4 → Ba3(PO4)2 + 6NaBr
• NOTE – We must always convert to moles to
cross the mole bridge!
Example
• What volume of CO2(g) at STP is produced if
1.35L of 0.100M HCl reacts with excess
CaCO3?
Titration
• It is a special process we use to find an
unknown concentration of a chemical
• We can do this if we know the EXACT VOLUME
and CONCENTRATION of one species and the
VOLUME of our unknown species
• We use a tool called a burette (will use a lot in
chemistry 12)
Equivalence point or stoichiometric
point
• This is the point when the molar ratio between
our known species and unknown species meet
the molar ratio of the balanced reaction!
• Their mole ratio matches the coefficients!
• We use an indicator that changes colour when
the equivalence point is met! (more on this in
chemistry 12)
• One indicator is phenolphthalein, the indicator
that turns pink!
Example
• H2SO4 + 2NaOH → Na2SO4 + 2H2O
• For this example, our equivalence point is met
when 1 mole of H2SO4 is reacted with 2 moles
of NaOH. Any ratio of 1:2 will work
• This means if we have a known concentration
of 0.05mol of H2SO4. We will need 0.10 mol of
NaOH to meet its equivalence point!
Example
• It takes 19.54mL of 0.50M BaBr2 to titrate
25.0mL of Na3PO4. Find [Na3PO4]
Remember
• In a titration, the equivalence point is when
the mole ratios are met!
• 3A + 2B → 3C
• The equivalence point is met when we have
any ratio of 3A to 2B.
Homework
• Page 131 #17-25 (odd only)