Solutions and Solution
Stoichiometry
Parts of Solutions
• Solution- homogeneous mixture.
• Solute- what gets dissolved.
• Solvent- what does the dissolving
• Water as solvent = aqueous solutions
• Soluble- Can be dissolved.
• Miscible- liquids dissolve in each other.
Water’s Unique Properties
• Water is a good solvent because
the molecules are polar.
• The angle is approximately 105º.
• The oxygen atoms have a partial
negative charge.
• The hydrogen atoms have a
partial positive charge.
• Water will attract ions and other
polar substances
General Properties of Aqueous
Solutions
Electrolytic Properties
• Aqueous solutions, solutions in water,
have the potential to conduct electricity.
• The ability of the solution to conduct
depends on the number of ions in solution.
• There are three types of solution:
– Strong electrolytes
– Weak electrolytes
– Nonelectrolytes
General Properties of Aqueous
Solutions
Ionic Compounds in Water
• Ions dissociate in water.
• In solution, each ion is surrounded by water
molecules.
• Transport of ions through solution causes flow of
current.
General Properties of Aqueous
Solutions
Strong and Weak Electrolytes
• Strong electrolytes: completely dissociate in
solution.
NaCl(aq)  Na+(aq) + Cl-(aq)
• Weak electrolytes: produce a small concentration
of ions when they dissolve. These ions exist in
equilibrium with the unionized substance.
HC2H3O2 (aq)
H+(aq) + C2H3O2-(aq)
General Properties of Aqueous
Solutions
Molecular Compounds in Water
• Molecular compounds in water (e.g., CH3OH): no
ions are formed.
• If there are no ions in solution, there is nothing to
transport electric charge.
Acids
Have a sour taste. Vinegar owes its taste to acetic acid. Citrus
fruits contain citric acid.
Cause color changes in plant dyes (indicators).
React with certain metals (see activity series) to produce H2 (g).
2HCl (aq) + Mg (s)
MgCl2 (aq) + H2 (g)
React with carbonates and bicarbonates to produce carbon
dioxide gas
2HCl (aq) + CaCO3 (s)
CaCl2 (aq) + CO2 (g) + H2O (l)
Aqueous acid solutions conduct electricity.
Acids
Memorize this list!
• Strong Acids
–
–
–
–
–
–
Nitric acid
Sulfuric acid
Chloric acid
Hydrochloric acid
Hydrofluoric acid
Hydroiodic acid
Or memorize this list
• Weak Acids
– Every other acid
Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.
Cause color changes in plant dyes (indicators).
Aqueous base solutions conduct electricity.
Bases
Memorize this list!
• Strong Bases
– All soluble hydroxides
are strong bases
Weak Bases
– Every other base
– Know Ammonia (NH3)
Solubility of a Substance
• How much of a substance will dissolve in a
given amount of water.
• Usually measured in g/100 mL
• Solubility varies with temperature, but this
cannot be predicted for any given
substance except gases
– All gases become less soluble with increased
temperature of the water
Measuring Solutions
• Concentration- how much is dissolved.
moles solute
molarity (M) 
liters solution
1 mol solute
1M 
1 liter solution
Molarity
• Calculate the molarity of a solution with
34.6 g of NaCl dissolved in 125 mL of
solution.
Molarity
• What would the concentration be if you
used 27g of CaCl2 to make 500. mL of
solution?
• What is the concentration of each ion?
Molarity
• Calculate the concentration of a solution
made by dissolving 45.6 g of Fe2(SO4)3 to
475 mL.
• What is the concentration of each ion?
Making solutions
• Adding solutes can increase or decrease
the solution volume
• When making a solution, always dissolve
the solute in about 50% the desired water!
– Then add the remain water to bring the
solution to the desired level.
Making solutions
• Describe how to make 100.0 mL of a 1.0
M K2CrO4 solution.
Making solutions
• Describe how to make 250. mL of an 2.0
M copper (II) sulfate dihydrate solution.
Dilution
• Adding more solvent to a known solution.
• The moles of solute stay the same.
moles = M x L
M1 V1 = M2 V2
moles = moles
• A stock solution is a solution of known
concentration used to make more dilute
solutions
Dilution
• What volume of a 1.7 M solutions is
needed to make 250 mL of a 0.50 M
solution?
• 18.5 mL of 2.3 M HCl is added to 250 mL
of water. What is the concentration of the
solution?
• 18.5 mL of 2.3 M HCl is diluted to 250 mL
with water. What is the concentration of
the solution?
Dilution
• You have a 4.0 M stock solution. Describe
how to make 1.0L of a 0.75 M solution.
Solution Stoichiometry and
Chemical Analysis
• There are two different types of units:
– laboratory units (macroscopic units: measure in lab);
– chemical units (microscopic units: relate to moles).
• Always convert the laboratory units into chemical
units first.
– Grams are converted to moles using molar mass.
– Volume or molarity are converted into moles using M
= mol/L.
• Use the stoichiometric coefficients to move
between reactants and product.
Solution Stoichiometry and
Chemical Analysis
Solution Stoichiometry and
Chemical Analysis
Titrations
• Suppose we know the molarity of a NaOH
solution and we want to find the molarity of an
HCl solution.
• We know:
– molarity of NaOH, volume of HCl.
• What do we want?
– Molarity of HCl.
• What do we do?
– Take a known volume of the HCl solution, measure
the mL of NaOH required to react completely with the
HCl.
Solution Stoichiometry and
Chemical Analysis
Titrations
Solution Stoichiometry and
Chemical Analysis
Titrations
• What do we get?
– Volume of NaOH. We know molarity of the NaOH,
we can calculate moles of NaOH.
• Next step?
– We also know HCl + NaOH  NaCl + H2O.
Therefore, we know moles of HCl.
• Can we finish?
– Knowing mol HCl and volume of HCl (20.0 mL
above), we can calculate the molarity.
Solution Stoichiometry and
Chemical Analysis
Titrations
Titration Calculations
•
•
•
•
•
•
Start VolBase = 10.00 mL
End VolBase = 40.00 mL
Mb = 0.200 M
Vb = 30.00 mL
Va = 20.00 mL
Ma =
Solution Stoichiometry
• 25 mL 0.67 M of H2SO4 is added to 35
mL of 0.40 M CaCl2 . What mass CaSO4
is formed?