homework chapter 0 - 0, 1, 2, 4 chapter 1 – 15, 16, 19, 20, 29, 31, 34
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Homework
Chapter 0 - 0, 1, 2, 4 Chapter 1 – 15, 16, 19, 20, 29, 31,
34
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Question:
What is the molarity of a 10% (w/v) solution of glucose?
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Parts per million (PPM)Parts per million (PPM)
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PPMPPM Parts per million is a convenient way to
express dilute concentrations. Historically, 1 1 mg per litermg per liter or per 1000 ml is referred to as 1 ppm.1 ppm. However, this is not really the case, as parts per million should be expressed as:
solution g1,000,000m
solute mg = cppm
Show that the above equation is equivalent to mg per liter.Show that the above equation is equivalent to mg per liter.
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PPMPPM
solution g1,000,000m
solute mg = cppm
For dilute solutions, the density of the solution will be the same as water.For dilute solutions, the density of the solution will be the same as water.
Density of solution = Density of water=Density of solution = Density of water=1.0 g/ml1.0 g/ml
solution g1,000,000m
solute mg = cppm
solution 1g
solution 1000mg
solution 1ml
solution 1g
solution ml 1000
solute mg = cppm
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Question Question Converting PPM to MolarityConverting PPM to Molarity
The town of Canton prohibits the dumping of copper solutions that have concentrations greater than 0.3969 ppm. When cleaning the quant lab, Dr. Skeels found a bottle labeled “copper standard - 7 M”, is it permissible to dump this solution down the drain?
Volunteers??Volunteers??
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Preparation of Stock Solutions
Solids Liquids
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Solution preparation cont’d
Describe the Preparation of a 500.0 mL of a solution that contains 8.00 mM Cu2+ using CuSO4
.5H2O (MW 149.69).
L1
Cu mmol 8.00 2
mmol
mol
1000
1
L
mol
1
Cu 1000.8 23
L
mol
1
Cu 1000.8 23
224
Cu 1
5CuSO 1
mol
OHmolL
OHSmol
1
5OCu 1000.8 243
L
OHSmol
1
5OCu 1000.8 243
L5000.0 OHSmol 243 5OCu 1000.4
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Solution preparation cont’d
Describe the Preparation of a 500.0 mL of a solution that contains 8.00 mM Cu2+ using CuSO4
.5H2O (MW 149.69).
OHSmol 243 5OCu 1000.4
OHS
OHSg
24
24
5OCu mol 1
5OCu 69.249
OHSg 24 5OCu 999.0
Thus …
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Add ______g CuSO4.5H2O
Into a volumetric flask
Add about _____ ml of waterSwirl to dissolveAnd fill to the _____ ml mark
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Question
Using the 8 mM Cu2+ solution, prepare 20 mL of a 0.25 mM Cu2+ solution.
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Dilutions
To make dilutions of a solution, the following equation should be employed:
M V = M Vi i f f
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Question
Using the 8 mM Cu2+ solution, prepare 20 mL of a 0.25 mM solution.
M V = M Vi i f f mlmM 020.25mM=V8 i
mM
ml
8
020.25mM=Vi
0.625mL=
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From a liquid – consider concentrated HCl
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A more difficult example
Prepare a 500.0 mL of 1 M HCl.
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Wt %
MW
Density
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Try it out …
Consider it in two steps:(1) Determine concentration of Stock(2) Make dilution
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(1) Concentration of Stock
Must find grams of HCl per liter of solutionHCl=1.19 g/ml
MW=36.46 g/mol
%HCl (w/w)=37%
Solution 100
HCl 37
1
1000
solution
solution 19.1
g
g
L
ml
mL
g
MassHCl per Liter L
g HCl 1040.4 2
Molarity
L
g HCl 1040.4 2
HCl 46.36
HCl 1
g
mol M1.12
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Dilution
Determined concentration of stock is ______ M HCl. We want a 500.0 mL solution that is 1M.
ffii VM=VM mLM 0.0051M=V1.21 i
M
mL
1.21
0.0051M=Vi
41.322mL=
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NOTE
Care must be exercised when handling strong acids!!(Always, Always add acid to water)
Add about 300 ml of water firstThen add acidDilute to mark
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Homework
Chapter 0 - 0, 1, 2, 4 Chapter 1 – 15, 16, 19, 20, 29, 31,
34
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Chapter 3Chapter 3Experimental ErrorExperimental Error
And propagation of And propagation of uncertaintyuncertainty
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Suppose
You determine the density of some mineral by measuring its mass 4.635 + 0.002 g
And then measured its volume 1.13 + 0.05 ml
)(
)(
mlvolume
gmass
ml
g1018.4
What is its uncertainty?
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Significant Figures (cont’d)
The last measured digit always has some uncertainty.
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3-1 Significant Figures3-1 Significant Figures
What is meant by significant figures?
Significant figures:Significant figures: minimum number of digits required to express a value in scientific notation without loss of accuracy.
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Examples
How many sig. figs in:a. 3.0130 meters b. 6.8 daysc. 0.00104 poundsd. 350 milese. 9 students
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“Rules”
1. All non-zero digits are significant2. Zeros:
a. Leading Zeros are not significantb. Captive Zeros are significantc. Trailing Zeros are significant
3. Exact numbers have no uncertainty
(e.g. counting numbers)
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Reading a “scale”
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What is the “value”?
When reading the scale of any apparatus, try to estimate When reading the scale of any apparatus, try to estimate to the nearest tenth of a division.to the nearest tenth of a division.
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3-23-2Significant Figures in ArithmeticSignificant Figures in Arithmetic
We often need to estimate the uncertainty of a result that has been computed from two or more experimental data, each of which has a known sample uncertainty.
Significant figures can provide a marginally good way to express uncertainty!
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3-23-2Significant Figures in ArithmeticSignificant Figures in Arithmetic
Summations: When performing addition and subtraction
report the answer to the same number of decimal places as the term with the fewest decimal places
+10.001+ 5.32+ 6.130
?21.45121.451 ___ decimal places
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Try this one
1.632 x 105
4.107 x 103
0.984 x 106
+
0.1632 x 106
0.004107 x 106
0.984 x 106
+
1.151307 x 1061.151307 x 106
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3-23-2Significant Figures in ArithmeticSignificant Figures in Arithmetic
Multiplication/Division: When performing multiplication or division
report the answer to the same number of sig figs as the least precise term in the operation
16.315 x 0.031 = ?0.505765
___ sig figs ___ sig figs ____ sig figs
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3-23-2Logarithms and AntilogarithmsLogarithms and Antilogarithms
From math class:log(100) = 2Or log(102) = 2But what about significant figures?
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Between -5 and -4
3-23-2Logarithms and AntilogarithmsLogarithms and Antilogarithms
Let’s consider the following:An operation requires that you take the log of 0.0000339. What is the log of this number?
log (3.39 x 10-5) = -4.469800302log (3.39 x 10-5) = log (3.39 x 10-5) = ____ sig figs
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3-23-2Logarithms and AntilogarithmsLogarithms and Antilogarithms
Try the following:Antilog 4.37 =234422.3442 x 104
___ sigs___ sigs
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“Rules”
Logarithms and antilogs1. In a logarithm, keep as many digits to
the right of the decimal point as there are sig figs in the original number.
2. In an anti-log, keep as many digits are there are digits to the right of the decimal point in the original number.
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3-4. Types of error3-4. Types of error Error – difference between your answer and
the ‘true’ one. Generally, all errors are of one of three types. Systematic (aka determinate) – problem with the
method, all errors are of the same magnitude and direction (affect accuracy)
Random – (aka indeterminate) causes data to be scattered more or less symmetrically around a mean value. (affect precision)
Gross. – occur only occasionally, and are often large.
EstimatedEstimated
Treated statisticallyTreated statistically
Can be detected and Can be detected and eliminated or lessenedeliminated or lessened
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Absolute and Relative Absolute and Relative UncertaintyUncertainty
Absolute uncertainty expresses the margin of uncertainty associated with a measurement.Consider a calibrated buret which has an uncertainty + 0.02 ml. Then, we say that the absolute uncertainty is + 0.02 ml
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Absolute and Relative Absolute and Relative UncertaintyUncertainty
Relative uncertainty compares the size Relative uncertainty compares the size of the absolute uncertainty with its of the absolute uncertainty with its associated measurement. associated measurement.
Consider a calibrated buret which has an uncertainty is + 0.02 ml. Find the relative uncertainty is 12.35 + 0.02, we say that the relative uncertainty is
tmeasuremen of magnitude
yuncertaint absolutety UncertainRelative 002.0
12.35
0.02
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3-5. Estimating Random 3-5. Estimating Random Error (absolute uncertainty)Error (absolute uncertainty)
Consider the summation:
+ 0.50 (+ 0.02)+4.10 (+ 0.03) -1.97 (+ 0.05)
2.63 (+ ?)
Sy = + 0.06
...222 cbay ssss
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3-5. Estimating Random 3-5. Estimating Random ErrorError
Consider the following operation:
?)(010406.0)04.0(97.1
)0001.0(0050.0)02.0(10.4
...222
c
s
b
s
a
s
y
scbay
222
97.1
04.0
0050.0
0001.0
10.4
02.0
y
sy
02897.0y
syysy 02897.0 0.010406 =
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Try this one
)4.0(3.42)5(1030)10(820
)001.0(050.0)2.0(6.11)2.0(3.14
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3-5. Estimating Random 3-5. Estimating Random ErrorError
For exponents
a
sx
y
s
ay
For
ay
x
aS is ain y uncertaint
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3-5. Estimating Random 3-5. Estimating Random ErrorError
Logarithms antilogs
a
ss
ay
For
ay 434.0
S is ain y uncertaint
log
a
ay sy
s
aantiy
For
303.2
S is ain y uncertaint
log
a
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Question
Calculate the absolute standard deviation for a the pH of a solutions whose hydronium ion concentration is
2.00 (+ 0.02) x 10-4
pH = 3.6990 + ?
a
ss
ay
ay 434.0
S is ain y uncertaint
log
a
00.2
02.0434.0ys
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Question
Calculate the absolute value for the hydronium ion concentration for a solution that has a pH of 7.02 (+ 0.02)
[H+] = 0.954992 (+ ?) x 10-7
ay sy
s
aantiy
303.2
S is ain y uncertaint
log
a
yss ay 303.2
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Suppose
You determine the density of some mineral by measuring its mass 4.635 + 0.002 g
And then measured its volume 1.13 + 0.05 ml
)(
)(
mlvolume
gmass
ml
g1018.4
What is its uncertainty?
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The minute paper
Please answer each question in 1 or 2 sentences
1) What was the most useful or meaningful thing you learned during this session?
2) What question(s) remain uppermost in your mind as we end this session?