Transcript Slide 1

John E. McMurry • Robert C. Fay
C H E M I S T R Y
Sixth Edition
Chapter 3
Mass Relationships in Chemical Reactions
These Sections Will NOT be on EXAM 1
Concentrations of Reactants in
Solution: Molarity
Molarity: The number of moles of a substance dissolved in each liter of
solution. In practice, a solution of known molarity is prepared by
weighing an appropriate amount of solute, placing it in a container
called a volumetric flask, and adding enough solvent until an accurately
calibrated final volume is reached.
Solution: A homogeneous mixture.
Solute: The dissolved substance in a solution.
Solvent: The major component in a solution.
Concentrations of Reactants in
Solution: Molarity
Concentrations of Reactants in
Solution: Molarity
Molarity converts between mole of solute and liters of solution:
molarity =
moles of solute
liters of solution
1.00 mol of sodium chloride placed in enough water to make 1.00 L of
solution would have a concentration equal to:
1.00 mol
1.00 L
= 1.00
mol
L
or 1.00 M
Concentrations of Reactants in
Solution: Molarity
What is the molarity of a solution made by
dissolving 2.5 g of NaCl in enough water to make
125 ml of solution?
How many grams of solute would you use to prepare
1.50 L of 0.250 M glucose, C6H12O6?
Calculate the volume of a 0.80M potassium
bromide solution containing 23.6 g of potassium
bromide.
Diluting Concentrated Solutions
concentrated solution + solvent
dilute solution
initial
final
Mi Vi = Mf Vf
Or
M1V1 = M2V2
Since the number of moles of solute remains constant, all that changes is
the volume of solution by adding more solvent.
Diluting Concentrated Solutions
1.
Sulfuric acid is normally purchased at a concentration of 18.0 M.
How would you prepare 250.0 mL of 0.500 M aqueous H2SO4?
2.
To what volume should you dilute 0.200 L of a 15.0 M
NaOH solution to obtain a 3.00 M NaOH solution?
Solution Stoichiometry
aA + bB
Volume of
Solution of A
Molarity of A
Moles of
A
cC + dD
Moles of
B
Mole Ratio
Between A and B
(Coefficients)
Volume of
Solution of B
Molar Mass of
B
Solution Stoichiometry
What volume of 0.250 M H2SO4 is needed to react with 50.0 mL of 0.100 M
NaOH?
H2SO4(aq) + 2NaOH(aq)
Volume of
Solution of H2SO4
Molarity of
H2SO4
Moles of
H2SO4
Na2SO4(aq) + 2H2O(l)
Moles of
NaOH
Mole Ratio Between
H2SO4 and NaOH
Volume of
Solution of NaOH
Molarity of
NaOH
Example
 What is the minimum amount (L) of 6.0 M H2SO4
necessary to produce 25.0 g
Assumed H2SO4 is limited
2 Al(s) + 3 H2SO4(aq)  Al2(SO4)3(aq) + 3 H2(g)
Titration
Titration: A procedure for determining the concentration of a solution by
allowing a carefully measured volume to react with a solution of another
substance (the standard solution) whose concentration is known.
HCl(aq) + NaOH(aq)
NaCl(aq) + 2H2O(l)
Once the reaction is complete you can calculate the concentration of the
unknown solution.
How can you tell when the reaction is complete?
Titration
buret
Erlenmeyer
flask
standard solution
(known concentration)
unknown concentration solution
An indicator is added which changes color once
the reaction is complete
Titration
48.6 mL of a 0.100 M NaOH solution is needed to react with 20.0 mL of an
unknown HCl concentration. What is the concentration of the HCl solution?
HCl(aq) + NaOH(aq)
Volume of
Solution of NaOH
Molarity of
NaOH
Moles of
NaOH
NaCl(aq) + 2H2O(l)
Moles of
HCl
Mole Ratio Between
NaOH and HCl
Concentration
of HCl
Volume of
HCl
Example
 What volume (in mL) of a 0.150 M HNO3 solution is
required to completely react with 35.7 mL of a 0.108
M Na2CO3 solution according to the following
balanced chemical equation?
Na2CO3(aq) + 2 HNO3(aq)  2 NaNO3(aq) +
CO2(g) + H2O(l)