REVIEW Chapters 0-3,

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1 REVIEW Chapters 0-3, "When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge but you have scarcely, in your thoughts, advanced to the stage of science." William Thomson, Lord Kelvin, 1891 There are two possible outcomes: if the result confirms the hypothesis, then you've made a measurement. If the result is contrary to the hypothesis, then you've made a discovery. Enrico Fermi, Nobel Prize in Physics, 1938 Quantitative chemical analysis is the measurement of how much of a chemical substance is present. Qualitative analysis tells us what is present. SI Units, 1-1 CHEMICAL MEASUREMENTS derived units: non-si: volt electric potential 1 liter m 3 coulomb quantity of electricity hertz frequency Prefixes (every third power of 10; Star Wars: remember Yotta?)

2 -2- "Almost all the chemical processes which occur in nature, whether in animal or vegetable organisms, or in the nonliving surface of the earth,... take place between substances in solution." Friedrich Wilhelm Ostwald, 1890 (Nobel Prize for Chemistry in 1909 "in recognition of his work on catalysis and for his investigations into the fundamental principles governing chemical equilibria and rates of reaction".) Chemical Concentrations, 1-2 solute solvent solution molarity, M formality, F (we will frequently use this) weight percent parts per million (billion, trillion), ppm (ppb, ppt) Preparing Solutions, 1-3 molarity - number of moles of solute per liter of solution Note: when working with small amounts it is often easier to think in terms of mmol/ml EX 1. What mass of silver nitrate is needed to make 100. ml of a M AgNO 3 solution? (M AgNO3 = g mol -1 ) dissolve first then bring to volume EX 2. What is the molarity of a 250 ppm silver nitrate solution? (M AgNO3 = g mol -1 )

3 -3- Diluting/Mixing Solutions number of moles does not change n 1 = M 1 V 1 = M 2 V 2 = n 2 EX 3. What is the molarity of pure water? (M H2O = g mol -1, d = 1.00 g cm -3 ) EX 4. What is the molarity of the solution prepared by adding 29.0 ml of 17.4 M acetic acid to a 500-mL volumetric and filling to the mark with distilled water? EX 5. How would you prepare 1.5 L of 0.10 M H 2 SO 4 from a 16 M supply? EX 6. What is the molarity of the sodium chloride solution obtained from mixing 53 ml of 0.52 M NaCl with 62 ml of 0.47 M NaCl?

4 -4- Density in Molarity Calculations EX 7. A solution which is 5.50% (by mass) sulfuric acid (M = ) has a density of g cm -3. What is the molarity of the solution? Stoichiometry Calculations for Gravimetric Analysis, 1-4 useful for Exp. 2 and 3 TOOLS OF THE TRADE Glassware burets, 2-4 Though tolerance is 0.05 ml estimate to 0.01 ml after all air bubbles are expelled. The buret above reads 9.68 ml Burets are calibrated to deliver (TD) an indicated volume.

5 -5- volumetric flasks, 2-5 Volumetric flasks are calibrated to contain (TC) an indicated volume. pipets, 2-6 The (a) transfer pipet and the (b) measuring pipet (generally referred to as a Mohr pipet) are both calibrated to deliver (TD) an indicated volume. The TC and TD volumes also require a specified temperature which is usually 20 o C. Note the proper spelling of buret and pipet (not burette and pipette, we are not living in France).

6 -6- Filtration, 2-7 read over for first two gravimetric experiments, Exp. 2 and 3 Techniques of analytical filtration will begin with the first two experiments, Exps. 2 and 3. In gravimetric analysis one wants to quantitatively recover as much of the precipitate as is theoretically possible, often after filtering. Major approaches use either the gravity filtration pictured on the right, using properly folded filter paper, or suction filtration. In the latter a faucet aspirator will replace the trap. When using a conical funnel, the given manner of folding filter paper will allow the paper to fit snugly a- gainst the funnel to enable more rapid filtration. connected directly to aspirator no trap Drying, 2-8 The gravimetric experiments require bringing to constant mass where the cooling step will be done in a dessicator. Careful analytical work employing primary standards will require you to dry the standards, again a dessicator will be used.

7 -7- Stoichiometry of Titrations, balanced equation concentrations end point = equivalence point acid/base titrations The Phenolphthalein End Point reading a meniscus EX 8. A 25.0 ml sample of acetic acid (CH 3 COOH) requires ml of M NaOH to reach the phenolphthalein end point. What is the concentration of acetic acid? EX g of potassium acid phthalate (KHP, M = g/mol) that has been dissolved in water requires ml of an NaOH solution to reach the phenolphthalein end point. What is the molarity of the base? NaOH(aq) + KHC 8 H 4 O 4 (aq) NaKC 8 H 4 O 4 (aq) + H 2 O(l) place a piece of white paper or kimwipe under flask to better aid detection of endpoint

8 -8- oxidation-reduction titrations EX 10. The iron in a g sample of ore is quantitatively all converted to Fe(II) and then titrated with M KMnO 4. If ml is required to reach the endpoint what is the mass percent iron in the ore? (M Fe = g/mol) MnO 4 (aq) + 5 Fe 2+ (aq) + 8 H + (aq) Mn 2+ (aq) + 5 Fe 3+ (aq) + 4 H 2 O(l)