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‘Why’ said the Dodo, ‘the best way to explain it is to do it.’ Alice in Wonderland

WHY LABORATORY ?. ‘Why’ said the Dodo, ‘the best way to explain it is to do it.’ Alice in Wonderland Lewis Carroll . CHE 133. A brief review. THE EXERCISES LABORATORY MEASUREMENT Lengths, Weights, Volumes, Density HOUSEHOLD "CHEMICALS"

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‘Why’ said the Dodo, ‘the best way to explain it is to do it.’ Alice in Wonderland

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  1. WHY LABORATORY ? ‘Why’ said the Dodo, ‘the best way to explain it is to do it.’ Alice in Wonderland Lewis Carroll

  2. CHE 133 A brief review

  3. THE EXERCISES LABORATORY MEASUREMENT Lengths, Weights, Volumes, Density HOUSEHOLD "CHEMICALS" FoodDyes - Spectroscopy FoodDyes – Chromatography Alum – Synthesis Household Materials - Analysis Vanillyl Alcohol – Synthesis Fruit Juices – Acid Content Vinegar – Acid Content Baking Soda - Gasometry Baking Soda - Gravimetry NaHCO3

  4. xx.xxxx THE HARDWARE Pipet & Syringe Buret Beakers, Cylinders, Flasks Bunsen Burner Hot Plate Gas Syringe Melting Point Apparatus Analytical Balance Top Loading Balance Visible/UV Spectrophotometer pH Meter Infrared Spectrometer xx.xx Safety Goggles

  5. THE TECHNIQUES CHEMICAL ANALYSIS Volumetric Techniques Standardization Weighing (by difference) Gravimetric Analysis Flame Tests Spectrophotometry Gas Collection and Measurement Melting Points Qualitative Infrared Spectroscopy CHEMICAL SEPARATION Use solubility for separation Paper Chromatography Gravity and Vacuum Filtration CHEMICAL SYNTHESIS Alum Vanillyl Alcohol ANALYSIS OF EXPERIMENTAL DATA Measures of accuracy and precision Significant Figures Tabulation and Graphing of Data Prep’n of Solutions Quantitative Dilution Solution Transfer Titration

  6. THE “CHEMICALS” • H2O • Food Dyes – B1, B2, G3, Y5, Y6, R3, R40, Isopropyl Alcohol, Salt Water • Al, KOH, H2SO4, KAl(SO4)2·12H2O, KAl(OH)4, Al(OH)3 • Vanillyl Alcohol, Vanillin, NaBH4, NaOH, HCl • Na2CO3, Urea, Ascorbic Acid, Borax, Na2S2O3, KHTartrate, CaCO3, Aspirin, Citric Acid, Ammonia, Acetic Acid (vinegar), I2 • NaOH, Citric Acid, Phosphoric Acid, Acetic Acid, • KHPhthalate, other naturally occurring acids • NaHCO3, HCl, NaCl, CO2

  7. THE PRINCIPLES, LAWS & RULES OF THUMB • Stoichiometry* • Beer’s Law A = ε b c • Capillary Action - Qualitative • Devising Synthetic Pathways • Ideal Gas Law – (non-Ideality) PV= nRT • Henry’s Law si = k Pi • Vibration Frequency ν= (1/2π)(k/μ)½ * Balancing Chemical Equations – mole relationships On a LINEAR SCALE, human eye is capable of estimating the location of a mark lying between two smallest divisions to the nearest1/5 th of a division

  8. DEFINITIONS • Percent Transmittance %T = 100 It / I0 • Absorbance A = log (I0 / It) • A = 2.0000 – log (%T) • Absorptivity is the ε in Beer’s Law A = ε b c • Concentration c = amount / volume • E.g., mol/L, mmol/mL, lbs/ft3, etc. • Analytical Wavelength - λ at which Absorbance is a maximum • Retention Factor Rf = dspot / dsolv • Percent Yield %Y = act yield / stoich yield • pH pH = - log [ H+ ] • Acid Ionization Constant Ka = [ H+ ][ A- ]/[ HA ] • pKapKa = - log Ka

  9. The Final Quiz 2 Parts Part 1 – Details - 50% Acids in juice Acid in vinegar 100 points – 30 min Gasometry Gravimetry Part 2 – Concepts – 50% + Above Laboratory Measurement Food Dyes - Spectroscopy Food Dyes – Chromatography Synthesis of Alum, Household Materials - Analysis Vanillyl Alcohol - Synthesis

  10. Acids in beverages

  11. HOW DOES THE STRENGTH OF AN ACID AFFECT ITS TITRATION CURVE pH pH at equivalence point changes with pKa Volume of added NaOH

  12. In the exercise we made two measurements: • 1.)Determined the TOTAL AMOUNTOFACID in a measured sample of the beverage by titrating the acid(s) with NaOH of known concentration. • The NaOH reacted with ALL OF THE ACID*, dissociated, or not. This told us the TOTAL of the DISSOCIATED + UNDISSOCIATED ACID in the beverage. * We did not detect any acids with pKa’s > 9, - the pH at which phenolphthalein signals its end point

  13. pH = -log [ H+] 2. Measured pH of a beverage to determine the actual H+ concentration of the beverage using a pH METER – (electronic device designed to measure the hydrogen ion concentration in aqueous solutions) This told us the CONCENTRATION OF DISSOCIATEDH+in the beverage, [ H+ ] = 10-pH

  14. Acid in vinegar

  15. PROCEDURE • A. STANDARDIZATION • Prepared solution of known concentration of primary standard, KHP* • Weighed out sample BY DIFFERENCE • Brought to total volume in VOLUMETRIC FLASK** • Calculate concentration of KHP • = wt KHP mg/(204.2 mg/mmol x VH2O mL) • = 3087.0 / (204.2 x 250.0) • = 0.06047 M KHP ~ 3g 250.0 mL or, = 3.0870 g / (204.2 g/mol x 0.2500 L) K * potassium hydrogen phthalate

  16. PROCEDURE Determineconcentration of stock NaOH Solution ( Nominally0.1 M ) Titrate measured volumes of standard KHP solution (known concentration) • with KHP NaOH measured volumes of NaOH Solution (unknown concentration) • (Delivered from • buret 1 ) (Delivered from buret 2 ) K+ + HP- + OH-→K+ + P= + H2O

  17. CALCULATIONS – NaOH STANDARDIZATION Molarity of KHP Solution: 0.06047 M KHP buret reading, final 37.44 mL 38.77 KHP buret reading, initial 3.68 mL 4.73 Volume of KHP titrated 33.76 mL34.04 NaOH buret reading, final 28.73 mL 31.83 NaOH buret reading, initial 4.52 mL 7.88 Volume of NaOH used 24.21 mL 23.95 mmol of KHP titrated 33.76 mL X 0.06047 M = 2.042 mmol 2.202 mmol of NaOH used 2.042 mmol 2.202 Molarity of NaOH 2.042mmol / 24.21mL = 0.08435M 0.08526 M Stoichiometry is 1 to 1 As Prepared

  18. CALCULATIONS - UNKNOWN Volume of Unknown 5.00 mL5.00 5.00 Concentration of NaOH solution 0.08435 M NaOH buret, final 22.47 mL 21.16 23.72 NaOH buret, initial 3.15 mL 2.374.22 Volume NaOH used 19.32mL18.79 19.50 mmol of NaOH used 19.32 * 0.08435 = 1.630 mmol 1.585 1.645 mmol of Acetic Acid titrated = 1.630mmol1.585 1.645 Acetic Acid Concentration 1.646/ 5.00 = =0.326 M 0.317 0.329 36 Stoichiometry is 1 to 1 3 Sig Figs From Standardization HOAc + OH-→ OAc-+ H2O

  19. Gasometric NaHCO3

  20. Gasometric Determination of NaHCO3 in a Mixture NaHCO3 (s) + H+  Na+ (aq) + H2O (l) + CO2 (g) Cl- Cl- Ideal Gas Law Henry’s Law Vapor Pressure nCO2g = (P – PH2O) VCO2 / RT PH2O,T, vI, nair PH2O,T, vF, nair, P P nCO2g nCO2s

  21. From Table Calculated Measured Calculations Weight of Sample0.2147 g Volume of gaseous CO2v45.7 mL Pressure, P = 752 mm Hg = 0.989 atm Temperature, T = 23oC = 296 K PH2O@ 23oC - 21 mm Hg 0.028 atm mmol CO2 (gas) = (P - PH2O)v / RT 1.81 mmol mmol CO2 (liquid) (Henry’s Law) ??????

  22. To calculate the Henry’s Law correction, we need the volume of the System. Suppose it is 100.0 mL That makes the initial volume, VI = 100.0 -10.0 + 5.0 = 95.0 mL Vsys = 100.0 mL Syringe: Initial = 5.0 mL Final = 50.7 mL and the final volume, VF = 100.0 -10.0 + 50.7= 140.7 mL PCO2= nCO2g RT / vF = ( P - PH2O)( 1 – vI / vF) = ( 0.989 – 0.028)( 1 – 95.0 / 140.7) Volume of HCl = 0.312 atm SCO2 = kHX PCO2 Concentration SCO2= 3.2 X 10-2 mmol/mL-atmX 0.312 atm = 0.010 M nCO2s = Volume X Concentration Amount = 0.10 mmol = 10.0 mL X 0.010 mmol/mL

  23. Calculated Calculations Weight of Sample0.2147 g Volume of gaseous CO2v45.7 mL Pressure, P = 752 mm Hg = 0.989 atm Temperature, T = 23oC = 296 K PH2O@ 23oC (from Table) 21 mm Hg 0.028 atm mmol CO2 (gas) = (P - PH2O)v / RT 1.81 mmol mmol CO2 (liquid) (Henry’s Law) 0.10 mmol Tot CO2 1.91 mmol mmol NaHCO3 (from stoichiometry) 1.91 mmol Weight of NaHCO3 1.91 X 84.0 0.160 g % NaHCO3 = 100 X 0.160 / 0.2147 = 74.5 %

  24. A simple example of Henry’s Law Dissolved Oxygen in Water: The Henry’s Law constant, kH, for Oxygen in water at 10 oC is 1.3 X 10-3M/atm. A sealed water bottle has a total volume of 450 mL and is filled with 400 mL of water. What is the total mg of O2in the sealed bottle? P = 1.0 atm ; T = 10 oC; R = 0.0821 mL-atm/mmol-K; PH2O = .012 atm at 10 oC (Air is about 20% oxygen, so PO2 ~ 0.20 atm.) CO2 = kH X PO2= 1.3 X 10-3M/atm X 0.20 atm = 2.6 X 10-4M mmol O2 = 2.6 X 10-4M X 400 mL = 0.10 mmol in water M = mmol/mL nO2 = PO2 v / RT = 0.20 X 50 / 0.0821 X 283 = 0.43mmol in gas mg O2 = (0.43 + 0.10 ) mmol X 32 mg/mmol = 17 mg

  25. Gravimetric NaHCO3

  26. Gravimetric Determination of NaHCO3 in a Mixture 2 NaHCO3 (s)  Na2CO3 (s) + H2O (g) + CO2 (g) Thermal Decomposition Constant Weight

  27. This Part of the Exercise is, again ConceptuallySimple. • Weigh Sample, wSample. 2. Decompose the sample by heating 2 NaHCO3 (s) 2 NaHCO3 (s)  Na2CO3 (s) + H2O (g) + CO2 (g) + NaCl(s) + NaCl(s) 3. Weigh product to get weightof CO2 & H2O lost weight loss = wCO2 + wH2O weight loss = nCO2 * 44.01 + nH2O * 18.02 Molar Massof CO2 Molar Mass of H2O weight = mol X Mol Mass

  28. 4. Get moles of CO2 , H2O and NaHCO3 lost 2 NaHCO3 (s)  ½Na2CO3 (s) + ½ H2O (g) + ½ CO2 (g) ½ ½ ½ nCO2 = nH2O= ½ nNaHCO3 (= nCO2 * 44.01 + nH2O * 18.02 ) so, weight loss = ½ nNaHCO3 * ( 44.01 + 18.02 ) or, nNaHCO3 = 2 * ( weight loss ) / 62.03 Molar Mass of NaHCO3 5.wNaHCO3 = nNaHCO3 * 84.01 g / mol 6. Compute Percent Composition of Sample PctNaHCO3 = 100 * wNaHCO3 / wSample

  29. How is Pct NaHCO3 related to the weight loss? wNaHCO3 = nNaHCO3 * 84.01 g / mol Showed that: 2 * ( weight loss ) 62.03 nNaHCO3 = 2 * ( weight loss ) 62.03 wNaHCO3 = X 84.01 = 2.709 * ( weight loss ) wNaHCO3= ( weight loss ) / 0.3691 PctNaHCO3 = 100 * wNaHCO3 / wSample = 270.9 * ( weight loss) / wSample

  30. wNaHCO3= ( weight loss ) / 0.3691 How much weight would 1.000 g of pure NaHCO3 lose? wNaHCO3 = 1 g 1 g = ( weight loss ) / 0.3691 weight loss = 0.3691 g PctNaHCO3 = 100 * wNaHCO3 / wSample 270.9 * ( weight loss) / wSample = 270.9 * 0.3691/ 1.000 = 100.0 %

  31. DATA SHEET Wt of crucible + sample 16.0755 g Wt of crucible 14.9842 g Wt of sample 1.0913 g Wt of evap dish + residue –after heat 15.8689 g Wt of residue [ 15.8689 – 14.9842 ] 0.8847 g Wt loss [ 1.0913 – 0.8847 ] 0.2066 g Wt NaHCO3 [ 0.2066 / 0.3691 ] 0.5597 g % NaHCO3 [100 X 0.5597 / 1.0913 ] 51.29 % Wt loss per gram of NaHCO3

  32. The Final Quiz Part 1 - Details Acids in Juice Acid in Vinegar Gasometry Gravimetry Part 2 - Concepts Laboratory Measurement Food Dyes - Spectroscopy Food Dyes – Chromatography Synthesis of Alum, Household Materials - Analysis Vanillyl Alcohol - Synthesis

  33. Laboratory Measurement • Concepts: • Measurement Uncertainty Linear • Mass/Weight Volume Density • Deliver/Contain Meniscus Homogeneity • Accuracy Precision Average • Significant Figures Average Deviation • Percent Error Error Propagation

  34. RULE OF THUMB: On a LINEAR SCALE, human eye is capable of estimating the location of a mark lying between two smallest divisions to the nearest1/5 th of a division You also explored the intrinsic errors and precision limitations of a number of common laboratory devices and the importance of recognizing both limitations and capabilities of measurement devices and sig figs as a representation.

  35. Analytical BalanceYY.XXXX Top Loading Balance Y.XX 50 mL Graduated Cylinder YY.X Buret YY.XX

  36. Simple Statistical Measures AVERAGE: M1 + M2 + …. + Mn n AVERAGE DEVIATION: |M1 – AVG| + |M2 – AVG| + … + |Mn – AVG| n PERCENT DEVIATION: 100 X AVG DEV AVG

  37. Spectroscopy of Food Dyes Concepts: Concentration Transmittance Absorbance Analytical Wavelength Beer’s Law Blank Spectrum Absorptivity vis/uv = electronic A= ε bc This wavelength is called the ANALYTICAL WAVELENGTH

  38. Chromatography of Food Dyes Concepts: chromatography mobile phase migration rate stationary phase solvent front resolution retention factor capillary action solvents Solvent Front dspot Rf = ------------- dsolvent dsolvent dspot Origin Some solvents are better than others

  39. Alum Synthesis M(I) T(III) (SO4)2.12 H2O 2 Al (s) + 2 OH- + 6 H2O  2 Al(OH)4- + 3H2 (g) Al(OH)4- + H+ H2O + Al(OH)3(s) Al(OH)3(s) + 3 H+ + 3 H2O  Al(H2O)63+ Synthesis Product Starting Material Yield Percent Yield Stoichiometry Water of crystallization Temperature dependence of solubility

  40. Identification of Household Chemicals CaCO3(s) + 2 H+ Ca2+ + H2O + CO2(g) CO3= (aq) + 2 H+ H2O + CO2(g) 2 S2O3= + I2 2I- + S4O6= C6H8O6 + I2 2I- + C6H6O6 + 2 H+ Carbonates react with acids to give off CO2 (g) sodium thiosulfate (hypo)  reducing agents  vitamin C (ascorbic acid) react with I2 to give I-

  41. Reduction of vanillin to vanillyl alcohol using NaBH4

  42. Net Effect: Addition of 2 H atoms aldehyde 4 4 vanillyl alcohol vanillin + BH4- + 4 H2O + H3BO3 sodium borohydride + OH- Theoretical yield Percent yield Reduction /H2 Stoichiometry Infrared absorptions Organic functional groups

  43. Vanillin IR Spectrum 1500 cm-1 – 4000 cm-1 IR = vibrations H H H O-H C-H3 X -H HC=O CC

  44. Some Common Calculations Solutions: mmols = Molarity * Volume (mL) Solids: mols = Weight / Molar Mass Dilutions: Conc1 * Volume1 = Conc2 * Volume2 Molarity1 * Volume1 = Molarity2 * Volume2 Gases: Pressurei * Volume = molsi * RT Pct Yield = 100 x Actual Yield/Theoretical Yield

  45. Some Possible Answers Yes a T 25oC F c All of the above Never 35% 3.1 X 10-5 b c Blue

  46. If you are continuing in CHE 134 Keep your: Safety Goggles Lock Towel ? The same Laboratory notebook can be used next semester.

  47. ACADEMIC CALENDAR - SPRING 2013 lecture CHE 134 LABSWILL NOT MEET during the first week of class (1/23 – 1/27). Monday Lecture does NOT meet on 1/28 Friday lecture DOES meet on 2/1 Students who fail to attend second weekLABmeetings will be de-registered (2/4 – 2/7)

  48. IF CLASSES ARE CANCELED CHECK THE COURSE WEBSITE or Blackboard

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