(Updated 111128) 1 Sample Questions for Chem 002 Final FS11 1. MSDS (the rest listed on review): a. Proper attire – b. Acid Spill – c. Bunsen Burners – d. Phenolphthalein – e. Types of radiation (listed below) are stopped by what type of material? alpha – beta – gamma – neutron – 2. Radioactive Decay: a. Determine if alpha or beta, then balance the following radioactive decay equations: (alpha / beta) 22286Rn → _____ + 42He (alpha / beta) 23490Th → _____ + 0-1e + anti-υ b. Determine the specific decay constant, initial activity and half-life of a radioactive isotope. Given the equations: A = Aoe-kt lnA = – kt + lnAo ln 2 = 0.693 t½ = ln2 / k y = mx + b m = (y2 – y1) / (x2 – x1) and the data: Time, minutes Counts/Min ln (Counts/Min) 0 2 14472 3 14328 4 14248 5 14095 6 13920 10 13359 1. Determine the specific decay constant, k, for this radioactive decay. 2. Determine the initial activity, Ao. 3. Determine the half-life.(Updated 111128) 2 3. Heat of Neutralization: A reaction of 100mL of 1.35M HCl and 100mL of 1.76M NaOH is monitored and the following temperatures were recorded: starting temperature = 24.6 oC; and final temperature = 38.8 oC. Calculate the ΔH of this reaction. Given: Cp of solution (J/K) = 4.13 J/( g . K)*Volume of solution in mL (1 mL ≈ 1 g for aqueous soln) Cp of calorimeter (J/K) = 50 Q = (-total Cp* ΔT) ΔT = Tf - Ti ΔH = Q/n n = # of moles reacted a. Determine the change in temperature for the system. b. Determine the Cp of the solution (J/K). c. Determine the total Cp of the system. d. Determine the number of moles of the acid and the base. Which is the limiting reagent? e. Determine the Heat Transfer, Q, for the reaction. f. Determine the change in enthalpy, ΔH, for the reaction.(Updated 111128) 3 4. Heat of Fusion. An ice cube with mass 9.53 grams (presume Ti = 0 oC) is placed in a calorimeter containing 111.24 grams of distilled water at a temperature of 23.2 oC. After equilibration, the final temperature was 15.8 oC. Given: ΔHtotal = ΔHice + ΔHwater + ΔHcalorimeter + ΔHfus = 0 ΔHwater (J) = Cp,H2O *(mass)*ΔT ΔHice (J) = Cp,ice *(mass)*ΔT Hcalorimeter (J) = Cp,Cal *ΔT Cp,H2O = 4.18 J/( g.oC) Cp,Cal = 50 J/oC ΔT = Tf - Ti a. Determine the ΔHwater. b. Determine the ΔHice. (Hint for Cp – The ice has melted.) c. Determine the ΔHcalorimeter. d. Determine the ΔHfus for one gram of ice. (Hint: For a calorimeter (i.e., closed systems) ΔHtotal = 0) 5. General Thermochemistry Concepts – a-d.) Circle appropriate answer. e-h.) Define: a. If heat transfers from the system (solute) to the surroundings (solvent), then ΔH is negative (ΔH < 0), and the reaction is defined as (endothermic / exothermic) and the temperature of the solvent will go (up / down). b. If heat transfers from the surroundings (solvent) to the system (solute), then ΔH is positive (ΔH > 0), and the reaction is defined as (endothermic / exothermic) and the temperature of the solvent will go (up / down). c. The heat of neutralization experiment was an (endothermic / exothermic) reaction . d. The heat of fusion experiment was an (endothermic / exothermic) reaction. e. This term means “the techniques that are used to measure enthalpy”: f. This term means “the energy needed to raise the temperature of an object 1o C”: g. This term means “the energy needed to raise the temperature of one gram of a substance 1o C”: h. The heat capacity is an extrinsic property. Define intrinsic and extrinsic properties and give an example of each.(Updated 111128) 4 6. Antacids: You are given 1.12 M HCl and 1.48 M NaOH. The antacid you use contains 300 mg of CaCO3 and 100 mg of Al(OH)3. If the antacid dissolved in 35.0 ml of HCl and was then back titrated with 21.8 ml of NaOH, find the following: a. The original number mmoles of HCl used to dissolve the antacid and neutralize the base. b. The number of mmoles of NaOH used to back titrate the acid. c. The number of mmoles of acid used to neutralize only the antacid (a.k.a. the excess HCl). d. Write the balanced equations for the neutralization of the antacid (Both CaCO3 and Al(OH)3 ). e. Using the number of mg in the tablet, calculate the mmoles of each component (Both CaCO3 and Al(OH)3 ). f. Based on the mmoles of each component, calculate the theoretical number of mmoles of HCl that should have been needed to neutralize the antacid. (Hint: Use the mole ratios.) g. What was the total number of theoretical mmoles of HCl that should have been neturalized? h. Calculate the percent error in order to compare the theoretical (g.) to the actual (c.). What are possible reasons this discrepancy could have occurred?(Updated 111128) 5 7. Spectrophotometry: Using a Spectrophotometer (Spec 20), a student recorded below the Percent Transmittance data for the following solutions: Red Dye Standard (6.30 ppm) Blue Dye Standard (5.05 ppm) Purple Unknown 400 nm 450 nm 500 nm 550 nm 600 nm 650 nm Red Std 63.5 48.5 23.5 38.6 78.3 98.5 Blue Std 80.5 99.0 82.5 56.5 8.5 72.4 Purple Unk 79.3 72.5 35.5 85.8 45.5 65.3 a. Calculate the Absorbance for each of the %T listed above . 400 nm 450 nm 500 nm 550 nm 600 nm 650 nm Red Std Blue Std Purple Unk b. Determine the following from the data calculated in Part 1 (2 pts): Red Dye Max. Absorbance = __________ at __________nm (λ Max) Blue Dye Max. Absorbance = __________ at __________nm (λ Max) c. Calculate the Absorbance Ratio of the Unknown/Standard at (λ Max). d. Calculate the Dye Concentration in the Unknown. (Standard Concentrations given above.) Abs of Unknown (at λ Max) Abs of Standard (at λ Max) Abs Ratio Unk/Std (at λ Max) Dye Conc. in Unknown Red in Purple Blue in Purple 8. Colorimetry: Using the well strips below, the student put the following number of drops in the wells. In strips I& II, 1-8 drops of blue dye standard solution (5.05 ppm) were added as shown in the diagram. In strip II, additional drops of water were added in order to have the same total volume of 8 drops for each well.