REVIEW

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REVIEW
Solution- a homogenous mixture of two or more
substances in a physical state.
Solute- the substance being dissolved.
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OBJECTIVE

• To acquire the skill of solving molarity problems.

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Hydration

• Hydration-when the positive ends of the water
  molecules (hydrogen) are attracted to the
  negatively charged anions and the negative ends
  (oxygen) are attracted to the cations. This
  causes the salt to fall apart.

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Electrolytes

• Strong electrolyte100 dissociate into ions
  conduct electricity.
• Weak electrolytepartially dissociate.
• Nonelectrolyteno ions in solution dont conduct
  electricity.

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Determination

• Is it a salt?
• Is it an acid?
• Is it a base?
• Is it covalently bonded?

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General Rules

• Most salts are strong electrolytes.
• Most acids are weak. SA HCl, HBr, HI, HNO3,
  H2SO4, HClO3, and HClO4
• SB hydroxides of the alkali metals and heavy
  alkaline earth (Ca, Sr, Ba). NH3 is a weak
  electrolyte.
• Most other substances are nonelectrolytes

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Other Notes

• Two acids which are weak but decompose
  immediately are carbonic acid (H2CO3) and
  sulfurous acid (H2SO3). Carbonic acid is always
  written as CO2 H2O while sulfurous acid is
  always written as SO2 H2O.
• NH4OH is always written as NH3 H2O.

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Molarity (M)

• The number of moles dissolved in each liter
  of solution.

Molarity (M) moles of solute
liters of solution
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EXAMPLE 1
You have 125g of acetic acid (C2H4O2) dissolved
in water to prepare 1.50L of solution. Find the
molarity.
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125g C2H4O2
1 mol C2H4O2 60g C2H4O2
1.50L solution
125 mol C2H4O2
90L solution
1.39 mol C2H4O2 / L solution
1.39 M C2H4O2
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EXAMPLE 2
How many grams of bromine are needed to prepare
.500L of a .0100 M solution of bromine in water?
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.0100 mol Br2 1 L
159.8g Br2 1 mol Br2
.500 L
.799g Br2
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Example 3
What is the concentration of sodium ions when
15.0 mL of 0.300 M Na2SO4 and 10.0 mL of 0.100 M
NaCl are mixed?
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Example 3
Na2SO4 2 Na SO42- 0.300 moles Na2SO4
2 moles Na L
1 mol Na2SO4 0.600 moles Na 0.015 L
L .009 moles Na
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Example 3
NaCl Na Cl- 0.100 moles NaCl 1
moles Na L 1
mol NaCl 0.100 moles Na 0.01 L
L .001 moles Na
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Example 3
Total Na concentration is .009 .001 moles
Na .015 .010 L 0.400 M Na
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Example 4
A stock solution is prepared by dissolving 10.0
mg of NaCl in enough water to reach 100.0 mL. A
50.0 mL aliquot of this solution is diluted to a
final volume of 500.0 mL. What is the molarity
of Na in this solution?
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Example 4
--(.010 g NaCl)/(58.5 g/mol) 1.71 X 10-4 mol
NaCl. 1.71 X 10-4 mol NaCl/0.1 L 1.71 X 10-3 M
NaCl in stock solution.
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Example 4
--1.71 X 10-3 mol NaCl 0.050 L L NaCl 8.55
X 10-5 mol NaCl transferred out of stock
solution. -- 8.55 X 10-5 mol NaCl 0.5 L
1.71 X 10-4 M A stock solution is prepared by
dissolving 10.0 mg of NaCl in enough water to
reach 100.0 mL. A 50.0 mL aliquot of this
solution is diluted to a final volume of 500.0
mL. What is the molarity of Na in this solution?