Transcript Chemistry: The Study of Change

Types of solution stoichiometry problems
• Dilutions
• Gravimetric analysis
• Titrations
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Gravimetric Analysis
Determining % (by mass) of an element in an unknown ionic compound
1.
Dissolve unknown substance in water
2.
React unknown with known substance to form a precipitate
3.
Filter and dry precipitate
4.
Weigh precipitate
5.
Use chemical formula and mass of precipitate to determine amount of
unknown ion
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Example 4.7)
A 0.5662-g sample of an ionic compound
containing chloride ions and an unknown
metal is dissolved in water and treated
with an excess of AgNO3. If 1.0882 g of
AgCl precipitate forms, what is the
percent by mass of Cl in the original
compound?
47.51%
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4.71)
If 30.0 mL of 0.150 M CaCl2 is added to
15.0 mL of 0.100 M AgNO3, what is the
mass in grams of AgCl precipitate?
0.215 g AgCl
…now try 4.73!
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Titrations
In a titration a solution of accurately known concentration
is added gradually added to another solution of unknown
concentration until the chemical reaction between the two
solutions is complete.
Equivalence point – the point at which the reaction is complete
Indicator – substance that changes color at (or near) the
equivalence point
Slowly add base
to unknown acid
UNTIL
the indicator
changes color
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What volume of a 1.420 M NaOH solution is
required to titrate 25.00 mL of a 4.50 M H2SO4
solution?
WRITE THE CHEMICAL EQUATION!
H2SO4 + 2NaOH
volume acid
25.00 mL x
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acid
moles acid
4.50 mol H2SO4
1000 mL soln
x
rx
coef.
2H2O + Na2SO4
moles base
2 mol NaOH
1 mol H2SO4
x
M
base
volume base
1000 ml soln
1.420 mol NaOH
= 158 mL
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Example 4.8)
In a titration experiment, a student
finds that 23.48 mL of a NaOH solution
are needed to neutralize 0.5468 g of
KHP. What is the concentration (in
molarity, M) of the NaOH solution?
KHP = KHC8H4O4
Molar mass of KHP= 204.2 g
0.1141 M
…now try 4.77!
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Gases
Chapter 5: 130-167
Elements that exist as gases at 250C and 1 atmosphere
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Physical Characteristics of Gases
•
Gases assume the volume and shape of their containers.
•
Gases are the most compressible state of matter.
•
Gases will mix evenly and completely when confined to the same
container.
•
Gases have much lower densities than liquids and solids.
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