1. Homework
Chapter , 1, 2, 4
Chapter 1 – 15, 16, 19, 20, 29, 31, 34

2. Question:
What is the molarity of a 10% (w/v) solution of glucose?

3. Parts per million (PPM)

4. PPM
Parts per million is a convenient way to express dilute concentrations. Historically, 1 mg per liter or per 1000 ml is referred to as 1 ppm. However, this is not really the case, as parts per million should be expressed as:
Show that the above equation is equivalent to mg per liter.

5. PPM
For dilute solutions, the density of the solution will be the same as water.
Density of solution = Density of water=
1.0 g/ml

6. Question Converting PPM to Molarity
The town of Canton prohibits the dumping of copper solutions that have concentrations greater than ppm. When cleaning the quant lab, Dr. Skeels found a bottle labeled “copper standard - 7 mM”, is it permissible to dump this solution down the drain?
Volunteers??

7. Preparation of Stock Solutions
Solids
Liquids

8. Solution preparation cont’d
Describe the Preparation of a mL of a solution that contains 8.00 mM Cu2+ using CuSO4.5H2O (MW ).

9. Solution preparation cont’d
Describe the Preparation of a mL of a solution that contains 8.00 mM Cu2+ using CuSO4.5H2O (MW ).
Thus …

10. Add ______g CuSO4.5H2O
Into a volumetric flask
Add about _____ ml of water
Swirl to dissolve
And fill to the _____ ml mark

11. Question
Using the 8 mM Cu2+ solution, prepare 20 mL of a 0.25 mM Cu2+ solution.

12. Dilutions
To make dilutions of a solution, the following equation should be employed:

13. Question
Using the 8 mM Cu2+ solution, prepare 20 mL of a 0.25 mM solution.

14. From a liquid – consider concentrated HCl

15. A more difficult example
Prepare a mL of 1 M HCl.

16. MW
Wt %
Density
Neatly on whiteboard …

17. Try it out … Consider it in two steps:
(1) Determine concentration of Stock
(2) Make dilution

18. (1) Concentration of Stock
Must find grams of HCl per liter of solution
dHCl=1.19 g/ml
%HCl (w/w)=37%
MW=36.46 g/mol
Mass
HCl per
Liter
Molarity

19. Dilution
Determined concentration of stock is ______ M HCl. We want a mL solution that is 1M.

20. NOTE Care must be exercised when handling strong acids!!
(Always, Always add acid to water)
Add about 300 ml of water first
Then add acid
Dilute to mark

21. Homework
Chapter , 1, 2, 4
Chapter 1 – 15, 16, 19, 20, 29, 31, 34

22. Experimental Error And propagation of uncertainty
Chapter 3
Experimental Error
And propagation of uncertainty

23. Suppose
You determine the density of some mineral by measuring its mass g
And then measured its volume ml
What is its uncertainty?

24. Significant Figures (cont’d)
The last measured digit always has some uncertainty.

25. 3-1 Significant Figures What is meant by significant figures?
Significant figures: minimum number of digits required to express a value in scientific notation without loss of accuracy.

26. Examples How many sig. figs in: 3.0130 meters 6.8 days 0.00104 pounds
350 miles
9 students

27. “Rules” All non-zero digits are significant Zeros:
Leading Zeros are not significant
Captive Zeros are significant
Trailing Zeros are significant
Exact numbers have no uncertainty
(e.g. counting numbers)

28. Reading a “scale”

29. What is the “value”?
When reading the scale of any apparatus, try to estimate to the nearest tenth of a division.

30. 3-2 Significant 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!

31. 3-2 Significant 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
21.451
21.451
___ decimal places ?

32. Try this one
1.632 x 105
4.107 x 103
0.984 x 106
x 106
x 106
x 106 + +
x 106
x 106

33. 3-2 Significant 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
x = ?
___ sig figs
___ sig figs
____ sig figs

34. 3-2 Logarithms and Antilogarithms
From math class:
log(100) = 2
Or log(102) = 2
But what about significant figures?

35. 3-2 Logarithms and Antilogarithms
Let’s consider the following:
An operation requires that you take the log of What is the log of this number?
log (3.39 x 10-5) =
log (3.39 x 10-5) =
log (3.39 x 10-5) =
Between -5 and -4
____ sig figs

36. 3-2 Logarithms and Antilogarithms
Try the following:
Antilog 4.37 =
x 104
23442
___ sigs

37. “Rules” Logarithms and antilogs
1. 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.

38. 3-4. 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.
Can be detected and eliminated or lessened
Estimated
Treated statistically

39. Absolute and Relative Uncertainty
Absolute uncertainty expresses the margin of uncertainty associated with a measurement.
Consider a calibrated buret which has an uncertainty ml. Then, we say that the absolute uncertainty is ml

40. Absolute and Relative Uncertainty
Relative uncertainty compares the size of the absolute uncertainty with its associated measurement.
Consider a calibrated buret which has an uncertainty is ml. Find the relative uncertainty is , we say that the relative uncertainty is

41. 3-5. Estimating Random Error (absolute uncertainty)
Consider the summation:
(+ 0.02)
(+ 0.03)
(+ 0.05)
Sy =
(+ ?)

42. 3-5. Estimating Random Error
Consider the following operation: =

43. Try this one

44. 3-5. Estimating Random Error
For exponents

45. 3-5. Estimating Random Error
Logarithms antilogs

46. 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 = ?

47. Question
Calculate the absolute value for the hydronium ion concentration for a solution that has a pH of 7.02 (+ 0.02)
[H+] = (+ ?) x 10-7

48. Suppose
You determine the density of some mineral by measuring its mass g
And then measured its volume ml
What is its uncertainty?

49. The minute paper Please answer each question in 1 or 2 sentences
What was the most useful or meaningful thing you learned during this session?
What question(s) remain uppermost in your mind as we end this session?