chemistry 7 - 4. hemoglobin, a protein in red blood cells ...4. hemoglobin, a protein in red blood...
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4. Hemoglobin, a protein in red blood cells, carries
O2, from the lungs to the body’s cells. Iron (as
Fe2+) makes up 0.33 mass % of hemoglobin. If the
molar mass of hemoglobin is 6.8x104 g/mol, how
many Fe2+ ions are in one molecule?
Assume 1 mol hemoglobin:
mass Fe2+ = 0.0033 (6.8x104 g mol-1) = 224.4 g
Looking at one molecule of hemoglobin:
mass Fe2+ in one molecule = 224.4 amu
# of Fe2+ ions = 224.4 𝑎𝑚𝑢
55.85 𝑎𝑚𝑢= 4.02
4 Fe2+ per molecule of hemoglobin
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Solution Stoichiometry
A solution is a homogenous mixture of a
solvent plus a solute.
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Concentration of Solutions
Amount of solute present in a given
quantity of solvent or solution
Expressed as molarity
𝑀 = 𝑚𝑜𝑙𝑎𝑟𝑖𝑡𝑦 =𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒
𝑡𝑜𝑡𝑎𝑙 𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
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𝑔𝑟𝑎𝑚𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 =𝑚𝑎𝑠𝑠
𝑣𝑜𝑙𝑢𝑚𝑒
Example
Calculate the molarity of a solution that
contains 12.5 g of pure sulfuric acid
(H2SO4) in 1.75 L of solution (Molar mass
H2SO4 = 98.1 g)
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𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 =12.5 𝑔 𝐻2𝑆𝑂4
1 𝑚𝑜𝑙 𝐻2𝑆𝑂4
98.1 𝑔 𝐻2𝑆𝑂4
1.75 𝐿= 0.0728 M 𝐻2𝑆𝑂4
Concentration
An intensive (not extensive) property
◦ Independent of the volume of solution (like
density or temperature)
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Preparing Solutions in the
Laboratory
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Practice Problem
How many grams of KI is required to
make 500. mL of a 2.80 M KI solution?
Reworded: Suppose I have 500. mL of a
2.80 M KI solution. How many grams of
KI solute does it contain? (“It” meaning
the entire 500. mL volume.)
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Practice Problem
How many grams of KI is required to
make 500. mL of a 2.80 M KI solution?
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𝑔𝑟𝑎𝑚𝑠 𝐾𝐼
= 500. 𝑚𝐿1 𝐿
1000 𝑚𝐿
2.80 𝑚𝑜𝑙 𝐾𝐼
𝐿 𝑠𝑜𝑙𝑛
166 𝑔 𝐾𝐼
𝑚𝑜𝑙 𝐾𝐼
= 232 𝑔 𝐾𝐼
Practice Problem
Sucrose has a molar mass of 342.29 g/mol.
It is a fine, white, crystalline powder with
a pleasing, sweet taste. What is the
molarity of an aqueous solution made by
placing 75.5 g of 85% pure sugar in 500.00
mL of water?
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What does 3.5 M FeCl3 mean?
1. 3.5 mol of dry, 100% pure FeCl3
dissolved in 1.00 L total solution volume
2. [Fe3+] = 3.5 M and [Cl-] = 3 x 3.5 M
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Example
In 2 L of 0.20 M Al2(SO4)3, (a) what is the molarity of Al2(SO4)3? (b) How many moles of Al are there? (c) What is the molarity of [Al3+] and [SO4
2-] ions?
a. [Al2(SO4)3] = 0.20 M
b. mol Al = 2 L 0.20 mol
L= 0.4 mol Al
c. Al2 += 2 × 0.20M
and SO42 −
= 3 × 0.20M
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Example
Hydrochloric acid is sold commercially as
a 12.0 M solution. How many moles of
HCl are in 300.0 mL of 12.0 M solution?
𝑚𝑜𝑙 𝐻𝐶𝑙
= 300.0 𝑚𝐿1 𝐿
1000 𝑚𝐿
12 𝑚𝑜𝑙 𝐻𝐶𝑙
1 𝐿 𝑠𝑜𝑙𝑛
= 3.60 𝑚𝑜𝑙 𝐻𝐶𝑙
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Dilution
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Dilution
Add solvent to a concentrated solution
From higher molarity lower molarity
The solution volume increases while the
number of moles of solute remains the
same
𝑀𝑑𝑖𝑙 × 𝑉𝑑𝑖𝑙 = 𝑛𝑜 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 = 𝑀𝑐𝑜𝑛𝑐 × 𝑉𝑐𝑜𝑛𝑐
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Example
“Isotonic saline” is a 0.15 M aqueous
solution of NaCl. How would you
prepare 0.80 L of isotonic saline from a
6.0 M stock solution?
𝑀𝑑𝑖𝑙 × 𝑉𝑑𝑖𝑙 = 𝑛𝑜 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 = 𝑀𝑐𝑜𝑛𝑐 × 𝑉𝑐𝑜𝑛𝑐
0.15 𝑀 0.80 𝐿 = 6.0 𝑀 𝑉𝑐𝑜𝑛𝑐
𝑉𝑐𝑜𝑛𝑐 = 0.02 𝐿 = 20. 𝑚𝐿
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A 0.020 L portion of the concentrated solution must be
diluted to a final volume of 0.80 L.
Practice Problem
1. Calculate the maximum number of
moles and grams of H2S that can form
when 158 g of aluminum sulfide reacts
with 131 g of water:
Al2S3 + H2O Al(OH)3 + H2S [unbalanced]
What mass of the excess reactant remains?
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Practice Problem
2. Sodium borohydride (NaBH4) is used
industrially in many organic syntheses.
One way to prepare it is by reacting
sodium hydride with gaseous diborane
(B2H6). Assuming an 88.5% yield, how
many grams of NaBH4 can be prepared
by reacting 7.98 g of sodium hydride and
8.16 g of diborane?
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Practice Problem
3. Calculate each of the following
quantities:
a. Volume in milliliters of 2.26 M potassium
hydroxide that contains 8.42 g of solute
b. Number of Cu2+ ions in 52 L of 2.3 M
copper(II) chloride
c. Molarity of 275 mL of solution
containing 135 mmol of glucose
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Practice Problem
4. Calculate each of the following quantities:
a. Volume of 2.050 M copper(II) nitrate that must be diluted with water to prepare 750.0 mL of a 0.8543 M solution
b. Volume of 1.63 M calcium chloride that must be diluted with water to prepare 350. mL of a 2.86x10-2 M chloride ion solution
c. Final volume of a 0.0700 M solution prepared by diluting 18.0 mL of 0.155 M lithium carbonate with water
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Announcements
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Quiz # 3 on July 16 Tuesday
◦ Coverage: Chapter 3 – Stoichiometry of
Formulas and Equations
Long Test # 1 on July 18, Escaler Hall
(tentative)
◦ Coverage: Chapters 1-3
Problem Sets
Chapter Practice problems
1 6, 7, 8, 22, 24, 26, 30, 34, 47, 49, 53, 55
2 11, 13, 17, 33, 61, 65, 67, 69, 71, 73, 75
3 6, 10, 12, 14, 16, 18, 20, 23, 26, 28, 30, 32,
33, 38, 40, 41, 43, 45, 49, 51, 65, 66, 69, 71,
73, 75, 83, 85, 89, 93
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Practice on some MC questions:
http://www.mhhe.com/physsci/chemistry/silberberg/student/
olc/quiz.mhtml