Aqueous Reactions and Solution Stoichiometry

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Aqueous Reactions and Solution Stoichiometry
Chapter 4
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What is a solution?

• When the solvent is water,
• The solution is an aqueous solution

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Examples of Aqueous Solutions
A Cup of Coffee Coffee Sugar Water
Sea Water Salt other solutes Water
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Concentration
The general term concentration refers to the
quantity of solute in a standard quantity of
solution.
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Molar Concentration

• Molar concentration, or molarity (M), is defined
  as the moles of solute dissolved in one liter
  (cubic decimeter) of solution.

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An Example
Calculation of molarity from number of moles of
Solute and volume of the solution
A sample of 0.0341 mol iron(III) chloride,
FeCl3, was dissolved in water to give 25.0 mL of
solution. What is the molarity of the solution?
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An Example
Calculation of mass of the solute from molarity
and volume of the solution
How many grams of NaCl are required to prepare
500 ml of 0.2M aqueous solution?
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Diluting Solutions
Upon addition of water to a solution (dilution),
the number of moles of a given substance remains
constant
?? ni nf
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An Example
Preparation of dilute solutions from concentrated
stock solutions
For a 12M stock solution of HCl, how many ml of
this solution gives 500 ml of 1.00 M solution?
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Solution Stoichiometery
An Example
How many ml of 3.00 M HCl are required to react
with 30.00 g of Zn(s)?
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Answer
30.00 g
? (mole)
V
0.4588 moles
0.9176 moles
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Types of Solutions
What happens on the microscopic level when a
compound is dissolved in water?
Nature of the compound
Molecular Compound
Ionic Compound
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A model of a portion of sodium chloride crystal
Ionic Compounds
What Happens when sodium chloride is dissolved in
water?
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Dissociation of ionic compounds in water make
their solutions good conductors to electricity
(electrolytes)
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Molecular Compounds
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Methanol molecular compound dissolves in water
but does not dissociate to ions (nonelectrolytes)
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Weak Electrolytes
Produce small number of ions in aqueous solutions