AP Chemistry Podcast 1.4 Beer’s Law and Stoichiometry Problem Set

Solution Chemistry The Water Molecule is Polar

Polar Water Molecules Interact with the Positive and Negative Ions of a Salt

BaCI2 Dissolving

Preparation of a Standard Solution A chemist whishes to prepare 1.00L of a 0.200 M sodium hydroxide solution. Describe the steps, with calculations, necessary to complete this task starting with solid sodium hydroxide and distilled water.

Dilution of Solutions- M1V1 = M2V2 A Measuring Pipet (b) A Volumetric (transfer) Pipet You’ve been asked to prepare 150 ml of a 0.035M solution of sodium hydroxide from the 0.200M stock sodium hydroxide solution prepared earlier. Detail the steps necessary to complete this task.

Beer- Lambert Law Beer’s Law Relates the amount of light being absorbed to the concentration of the substance absorbing the light A=abc A = measured absorbance a = molar absorptivity constant (a characteristic of the substance being monitored). b = path length through which the light must pass. c = Molar concentration of the absorbing substance.

Beer’s Law Sample Problems 1. A solution with a concentration of 0.14M is measured to have an absorbance of 0.43. Another solution of the same chemical is measured under the same conditions and has an absorbance of 0.37. What is its concentration? 2. The following data were obtained for 1.00 cm samples of a particular chemical. What is the concentration of a 1.00 cm sample that has an absorbance of 0.60? Conc. (M) Abs. 0.50 0.69 0.40 0.55 0.30 0.41 0.20 0.27 3. The absorptivity of a particular chemical is 1.5/M·cm. What is the concentration of a solution made from this chemical if a 2.0 cm sample has an absorbance of 1.20?

Beer’s Law Sample Problems 4. Using the data from the graphing example in question #2, what are the concentrations of solutions with absorbances of 0.20, 0.33, and 0.47?  5. A solution is prepared to be 0.200M. A sample of this solution 1.00 cm thick has an absorbance of 0.125 measured at 470nm and an absorbance of 0.070 measured at 550nm. Calculate the concentrations of the following solutions: Sample Absorbance Wavelength Path length 1 0.055 470nm 1.00cm 2 0.155 3 0.120 550nm 4 0.048 5.00cm

Stoichiometry Problem Set Aluminum oxide is to be made by combining 5.00 g of aluminum with oxygen gas. How much oxygen is needed in moles? In grams? In liters? During its combustion, ethane (C2H6) combines with oxygen gas to give carbon dioxide and water. A sample of ethane was burned completely and the water that formed had a mass of 1.61 g. How much ethane, in moles and in grams, was in the sample? Chloroform, CHCl3, reacts with chlorine gas to form carbon tetrachloride and hydrogen chloride. In one experiment the reactants were initially presented in a ratio of 1 to 1 by mass; specifically, 25.0 g of CHCl3 was mixed with 25.0 g of Cl2 (g). Which is the limiting reactant? What is the maximum yield of carbon tetrachloride in moles and in grams?

Stoichiometry Problem Set 4. One of the steps in one industrial synthesis of sulfuric acid (H2SO4) from sulfur is the conversion of sulfur dioxide (SO2) into sulfur trioxide (SO3) by this reaction: 2SO2+O2  2SO3 In one “run,” 1.75 kg of SO2 was used and 1.72 kg of SO3 was isolated from the mixture of products. What was the percent yield? 5. A student needs 0.250 mol of NaCl and all that is available is a solution labeled “0.400 M NaCl.” What volume of the solution should be used? Give your answer in milliliters. 6. Describe how to prepare 250 mL of 0.200 M NaHCO3.

Stoichiometry Problem Set 7. How many milliliters of 0.114 M H2SO4 solution are necessary to completely neutralize 32.2 mL of 0.122 M NaOH? 8. Describe how to make 500 mL of 0.20 M NaOH from 0.50M NaOH.