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Homework

Homework. Chapter 0 - 0, 1, 2, 4 Chapter 1 – 15, 16, 19, 20, 29, 31, 34. Question: . What is the molarity of a 10% (w/v) solution of glucose?. Parts per million (PPM). PPM.

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Homework

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  1. Homework • Chapter 0 - 0, 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 0.3969 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 500.0 mL of a solution that contains 8.00 mM Cu2+ using CuSO4.5H2O (MW 149.69).

  9. 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). 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 500.0 mL of 1 M HCl.

  16. MW Wt % Density

  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 500.0 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 0 - 0, 1, 2, 4 • Chapter 1 – 15, 16, 19, 20, 29, 31, 34

  22. Chapter 3 Experimental Error And propagation of uncertainty

  23. 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 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. 3-2Significant 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. 3-2Significant Figures in Arithmetic • Summations: • When performing addition and subtraction report the answer to the same number of decimal places as the term with the fewestdecimal places +10.001 + 5.32 + 6.130 21.451 21.451 ___ decimal places ?

  32. 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 106 1.151307 x 106

  33. 3-2Significant 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

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

  35. 3-2Logarithms 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? -4.469800302 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. 3-2Logarithms and Antilogarithms • Try the following: Antilog 4.37 = 2.3442 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 + 0.02 ml. Then, we say that the absolute uncertainty is + 0.02 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 + 0.02 ml. Find the relative uncertainty is 12.35 + 0.02, we say that the relative uncertainty is

  41. 3-5. Estimating Random Error (absolute uncertainty) • Consider the summation: + 0.50 (+ 0.02) +4.10 (+ 0.03) -1.97 (+ 0.05) Sy = + 0.06 2.63 (+ ?)

  42. 3-5. Estimating Random Error • Consider the following operation: 0.010406 =

  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 = 3.6990 + ?

  47. 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

  48. 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 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?

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