It’s lecture 6 – the end of Chapt 3
• Announcements
• Solutions
• Molarity
• Dilutions
• Bonus Feature!
The chemical formula for the molecule shown is?
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C2H4O
C4O2H8
C4H8N2
C4H8O2
The empirical formula for the molecule shown is?
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C2H4O
C4H8O2
C2H4N
C4H8N2
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Announcements
• Seminar Friday – the new Dean
• End Chapt 3 today, start Chapt 4 Wed.
• What follows Chapt 4 ?
Recognizing Ionic
Compounds
Correction to my
correction
Figure 3-12 p.79
Solutions
• Solution – a homogeneous mixture of two or more
substances, in which one is called the solvent and the other
is the solute
– Solvent – main medium, what is there in the largest
quantity
– Solute – dissolved in the solvent
Sugar and Water
Sugar (solute); Water (solvent)
Blood
Many solutes; Water (solvent)
Solution or No Solution?
Sugar water
Solution
Muddy water
No Solution
Gasoline
Solution
Milk
No Solution
Concentration
• Concentration – the amount of a solute dissolved in a given
quantity of solvent
• A concentrated solution has a large amount of solute in it.
• A dilute solution has a small amount of solute in it.
• Measured quantitatively with a variety of units
– Most common is Molarity
Molarity
• Molarity – the number of moles of solute dissolved in 1 L
of solution
• To calculate molarity:
n
quantity of A (mol)
Molarity of A (M) =
=
Volume of Solution (L) V
For example: 68.5 G of sucrose (C12H22O11) are dissolved in
100.0 mL of water. What is the concentration?
Sucrose Example
68.5 G of sucrose (C12H22O11) are dissolved in 100.0 mL of water.
1. Find # moles of sucrose
a. Need molar mass of sucrose
12mol C
12.011g
22mol H
1.0079g
11mol O
15.999g
342.2948 g
×
+
×
+
×
=
1 mol Sucrose 1mol C 1 mol Sucrose 1mol H 1mol Sucrose 1mol O 1mol Sucrose
b. Now we can determine # moles sucrose
68.5 g Sucrose ×
2.
1 mol Sucrose
= 0.200120 mol Sucrose
342.2948 g Sucrose
Divide moles by volume to get concentration
n 0.200120 mol Sucrose
=
= 2.00120 Molar = 2.00 Molar
0.1000 L
V
(roughly maple syrup)
More solution info
• Dissolved substances are either molecules or ions
– Molecules are neutral (e.g. sucrose, some proteins,
caffeine)
– Ions are charged (e.g. Na+, NO3– , C2O42– )
• Many everyday solutions have water as the solvent
– These are aqueous solutions (aq)
Do you know your ions and solutions?
If 2 moles of ammonium sulfite are dissolved in 1 L of
water, what is true about the resulting solution?
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It is 2 M in SO42–
It is 4 M in N3+
It is 2 M in NH4+
None of the above
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Dilution
• Creating a solution that is less concentrated from one that is
more concentrated
• How do you make 4 L of tree sap from maple syrup?
– Syrup is about 2 M, tree sap is about 0.058 M
1.
Determine # moles of sucrose that are needed for dilute solution
0.058 M sucrose =
2.
0.058 mol sucrose
× 4 L solution = 0.232 mol sucrose
1 L solution
Determine volume of concentrated solution needed to get those moles
1 L solution
0.232 mol sucrose ×
= 0.116 L solution
2 mol sucrose
So, put 116 mL of syrup in a container and fill until the
total volume is 4 L.
Remember: You are done with the
homework when you understand it!
Today
• Finish CAPA #3
By Wednesday
• Get a start on CAPA set #4
• Read 4.1-4.2