Lab problems, Thanksgiving week, Fall 2014. Name: ____________________________________ Lab day: ____________________ Put answers on this sheet, but turn in legible written work on separate paper. 1. Dr. Banner is given the graph below for the UV analysis (280 nm) of a solution developed to reverse damage caused by radiation. Use the graph to determine the concentrations of solutions X and Y. a. Solution X was analyzed to have A = 0.285. b. Solution Y is too concentrated for analysis, so 10.00 mL of Y is pipetted into a volumetric flask and diluted with water to 25.00 mL. This diluted solution has A = 0.673. Find [Y] original. Absorbance vs. Concentration at 280 nm for Gamma-X 1a. _______________________ 1b. _______________________ 2. When chlorine dioxide gas reacts with liquid water, the products are aqueous chloric acid and hydrochloric acid. What mass of chloric acid, in kg, can be made from combining 62.5 kg of chlorine dioxide and 23.5 kg of water? What is the percent yield if 37.2 kg of chloric acid is formed? 2. ___________________________ 3. Calculate the molar concentration of a solution that is prepared by diluting 15.0 mL of a 2.50 μM DNA solution with 35.0 mL H2O. 3. ___________________________ 4. Calculate the volume, in mL, of 2.000 M KCl needed to make 250.0 mL of 0.3000 M solution. 4. ___________________________ 5. A 3+ ion of 195Au contains protons, neutrons, and electrons. 6. If a fixed amount of gas occupies 6.00 L at a temperature of -22.0°C and 215 torr, what volume will it occupy at 28.5°C and 1082 torr? 6. ___________________________ 7. The standard molar enthalpy change for the combustion of ammonia is –905.2 kJ. Calculate the standard molar enthalpy of formation for NH3, given the following equation and Hºf values. 4 NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) Hºf[NO(g)] = -+90.3 kJ/mol Hºf[H2O(g)] = -241.8 kJ/mol 7. __________________________ 8. The element Aragornium (Arg) has an average atomic mass of 99.55 amu. There are two isotopes of Arg; one has a natural abundance of 30.00% and an atomic mass of 96.00 amu. Determine the percentage and atomic mass of the 2nd isotope of Arg. 8. __________________________ 9. How many mL are equivalent to 7290 gmL? A gimliliter (gmL) is equal to 1×10–12 liters. 9. __________________________ 10. Lanthanum (La, atomic #57) can be purified by precipitation with fluoride ions. Calculate the minimum volume of 0.840 M NaF needed to precipitate the La3+ ions in 2.500 L of 0.200 M La(NO3)3 solution. 10. __________________________ 11. Radiation in the infrared region of the electromagnetic spectrum is the major output of heat lamps. How much energy (in kJ) is emitted from a lamp that puts out 4.34×1026 photons with a wavelength of 1252 nm? 11. __________________________ 12. What is the resulting pH of a solution if 150.0 mL of 0.300 M NaOH is mixed with 250.0 mL of 0.200 M HCl? (hint: write a balanced chemical equation and determine how many moles of the excess compound are left after the reaction) 12. __________________________ 13. Circle the substance that is being reduced in the following reaction? CeCl4(aq) + FeSO4(aq) → Ce3+(aq) + Fe3+(aq) + SO42–(aq) + 4Cl–(aq) 14. Assign oxidation numbers to each element in NH4MnO4 and CH3SH. 14. __________________________ 15. A compound having the empirical formula of CH2N is found experimentally to have a molar mass of 84.10 g/mol. Determine the compound’s empirical and molecular formulas. 15. __________________________ 16. Using molecular orbital theory, determine the bond orders and magnetic properties of CN and CN–. Which would have the strongest bond? B2 CN ∗ σ 2p ∗ π 2p σ2p π2p σ∗2s σ2s magnetic property: bond order: strongest?: – -2 CN B2

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