Part I MATCH the following procedures with the correct descriptions or pictures in Part II (not all are shown you should review these procedures from your laboratory notebook) - Gravimetric Analysis - Determining Reaction Rate and Order - Qualitative Analysis of Cations/Anions - Determining Equilibrium Constant Keq - Determining Molar Mass of Volatile Liquid - Determining Ka of Weak Acid - Determining Molar Mass of Gas - Determining E Cell Potential - Determining Freezing-Point Depression - Determining Heat of Formation / Calorimetry - Determining Melting-Point - Determining ConcentrationVolumetricAnalysis - Determining Water of Hydration and Percentage Composition Part II ANSWER the following questions about each laboratory technique. WHICH LAB? 1. a) Briefly describe the equipment and procedure used to determine the unknown above. Be sure to include the terms solute, solvent, solution, freezing-point, colligative properties. b) Draw and label the graph for the pure liquid and solution showing the freezing-point depression. c).the following data were obtained in an experiment designed to find the molar mass of a solute by freezing point depression. Solvent: para-dichlorobenzene Freezing point of pure solvent: 53.02 C Freezing point depression constant: 7.1 C/m Mass of para-dichlorobenzene: 24.80 g Mass of unknown substance: 2.04 g Freezing point of solution: 50.78 C i. Determine the freezing point depression, ΔTfp. ii. Calculate the molar mass of the unknown substance. 1
WHICH LAB? 2. a) Describe how you could, using the equipment in the diagram, determine the chloride ion concentration in a water sample. Include a balanced equation. b) If the volume of the water sample being tested is 50.0 ml and the mass of the dried precipitate obtained is 3.65 g, calculate the chloride ion concentration in the water sample in ppm. 2
WHICH LAB? 3. a) When 5.03 g of solid potassium hydroxide are dissolved in 100.0 ml of distilled water in a coffeecup calorimeter, the temperature of the liquid increases from 23.0 C to 34.7 C. The density of water in this temperature range averages 0.9969 g/cm 3. What is ΔH soln (in kilojoules per mole)? Assume that the calorimeter absorbs a negligible amount of heat and, because of the large volume of water, the specific heat of the solution is the same as the specific heat of pure water. 3
WHICH LAB? 4. a) Describe the equipment and procedure used to determine the unknown above. Be sure to use these terms titrant, analyte, indicator, endpoint, equivalence point, buret, Erlenmeyer flask, pipette tip b). 1. Draw and label the graph for these titrations 2. Label equivalence point 3. WHICH INDICATOR would you use to titrate and find the endpoint? - Strong Acid Titrated with Strong Base - Strong Acid Titrated with Weak Base - Weak Acid Titrated with Strong Base - Weak Base Titrated with Strong Acid 4
WHICH LAB? 5. a). Describe the equipment and method used to find the unknown above. Be sure to include the EQUATIONS you would use to find the unknown. Also the terms eudiometer, ideal and non-ideal. b). (AP 2009) A student was assigned the task of determining the molar mass of an unknown gas. The student measured the mass of a sealed 843 ml rigid flask that contained dry air. The student then flushed the flask with the unknown gas, resealed it, and measured the mass again. Both the air and the unknown gas were at 23.0 C and 750. torr. The data for the experiment are shown in the table below. Volume of sealed flask 843 ml Mass of sealed flask and dry air 157.70 g Mass of sealed flask and unknown gas 158.08 g (i) Calculate the mass, in grams, of the dry air that was in the sealed flask. (The density of dry air is 1.18 g/ L (at 23.0 C and 750. torr.) (ii) Calculate the mass, in grams, of the sealed flask itself (i.e., if it had no air in it). (iii) Calculate the mass, in grams, of the unknown gas that was added to the sealed flask. (iv) Using the information above, calculate the value of the molar mass of the unknown gas. 5
WHICH LAB? 6. a) Describe which of the above glassware and equipment that you would use to make a primary standard solution of copper II sulfate. b). Describe the procedure you would use to determine the concentration of an unknown solution of copper II sulfate using the primary standard you created above. 6
WHICH LAB? 7. a. Briefly explain HOW you would set-up an experiment to produce each of the graphs above. Describe how the independent variable, dependent variable, and the expected results. b. A version of the iodine clock reaction involves reaction of iodide ions with persulfate ions. 2I (aq) + S2O82 (aq) I2(aq) + 2SO42 (aq) The following rate data was collected by measuring the time required for the appearance of the blue color due to the iodine starch complex. Trial [I ] [S2O82 ] Reaction Time 1 0.040 M 0.040 M 270 sec 2 0.080 M 0.040 M 138 sec 3 0.040 M 0.080 M 142 sec 1. In each trial, the blue color appeared after 0.0020 M iodine (I2) had been produced. Calculate the reaction rate for each trial by dividing the concentration of iodine formed by the reaction time. 2. Compare trials 1 and 2 to determine the order of reaction with respect to iodide ions. How did the concentration of iodide ions change in these two trials, and how did the rate change accordingly? What is the reaction order for iodide? 3. Which two trials should be compared to determine the order of reaction with respect to persulfate ions? What is the reaction order for persulfate? 7
4. Write the rate law for this version of the iodine clock reaction. Could the rate law have been predicted using the coefficients in the balanced chemical equation? Explain. 8
8. WHICH LAB? 9. WHICH LAB? 9
10 a. WHICH LAB? 10 b. WHICH LAB? HOW IS THIS GRAPH DIFFERENT THAN #10 a? 10
11. WHICH LAB? 12. WHICH LAB? 11
**LAST LAB QUESTION TOUGH ONE!** *WHICH LAB? * FILL IN THE FLOW-CHART BELOW! 12
SOME SELECTED ANSWERS - 2. a) 2 b) 3. a) (100.0 ml H2O)(0.9969 g/ml) + 5.03 g KOH = 104.72 g qcalorimeter=mcsδt= (104.72 g) 4.184 Jg C (11.7 C) = 5130 J = 5.13 kj ΔHsoln=( 5.13 kj5.03 g)(56.11 g1 mol)= 57.2 kj/mol 4. A strong acid will react with a strong base to form a neutral (ph = 7) solution. - phenolphthalein A strong acid will react with a weak base to form an acidic (ph < 7) solution. methyl orange A weak acid will react with a strong base to form a basic (ph > 7) solution. bromthymol blue 5. i) m=dv= (1.18 g /L)(0.843 L) = 0.995 g ii) 157.70 g 0.995 g = 156.71 g iii) 158.08 g 156.71 g = 1.37 g 13
iv) n=pv/rt= 40.1 g/ mol 14