Chem 400 Cosumnes River College Spring 2020 Lab Exam Professor Russell Mass of filter paper 1.1763 g Mass of precipitate + filter paper 6.3261 g You must show all work for you calculations to receive credit. You may work on a separate piece of paper, but must submit all copies of your shown work with your exam. 1. EXPERIMENT 6: CONCENTRATION OF A BARIUM HYDROXIDE SOLUTION Suppose you wish to determine the molar concentration of a solution of barium hydroxide. You performed a conductimetric titration and a gravimetric analysis similar to the ones in your lab notebook. The conductimetric titration of a 24.3-mL sample of barium hydroxide solution with 2.23M H2SO4 produced the following titration curve: A. From the titration curve and the information above, write the balanced molecular equation for the reaction of barium hydroxide with H2SO4, with phases, and calculate the molarity of the Ba(OH)2 solution. Show your setup and answer, and then restate the answer on the line. (4pts) Molarity: _________________ B. During the conductimetric titration from Part A, a precipitate was also formed. The precipitate was filtered, washed, and allowed to dry to a constant weight. From the gravimetric data shown below, determine the molarity of the barium hydroxide solution. Show your setup and answer, and then restate the answer on the line. (4pts) Molarity: _________________ Chem 400 Cosumnes River College Spring 2020 Lab Exam Professor Russell 2. Calculate the average and standard deviation for the following values. Report your answers with the proper precision in both the average and standard deviation. (4pts) 1.98544g 1.94376g 2.00462g 1.94933g Average + stddev: ____________________ 3. EXPERIMENT 8: Draw the Lewis structure for KrCl2. Show the calculation of the formal charges for each atom and label each atom with the correct formal charge. (2pts) What is the electron geometry? (1pt) ____________________ What is the molecular geometry? (1pt) ____________________ What is the hybridization? (sp, sp3, etc.) (1pt) ____________________ What is/are the approximate bond angle/s? (1pt) ____________________ Chem 400 Cosumnes River College Spring 2020 Lab Exam Professor Russell 4. EXPERIMENT 1 PART 3 – STANDARD CURVES Use the standard curve information below to calculate the percent concentration of a solution with density 1.0260 g/mL. (3pts) Percent concentration: _______________________ 5. EXPERIMENT 2: Conductin the same reaction we did in experiment 2, write down the chemical equation and show your calculation to determine the limiting reagent when 8.3194g of Sodium bicarbonate is reacted with 26.3mL of 1.5M citric acid. Finally, calculate the theoretical grams of carbon dioxide gas produced. (6pts) y = 0.0063x + 0.9977 R² = 0.999 0.95 1 1.05 1.1 0.00 5.00 10.00 15.00 20.00 Density g/mL % NaCl Standard Curve Chem 400 Cosumnes River College Spring 2020 Lab Exam Professor Russell 6. EXPERIMENT 4 – AQUEOUS REACTIONS a. Give the balanced molecular, complete ionic and net ionic equation for each of these. You need to show the proper phases in your net ionic reaction. Then give an observation you would most likely see with this reaction. i. A solution of lithium sulfide is mixed with a solution of aluminum nitrate. (8pts) Net ionic equation, with phases ____________________________________ Accepted observation ____________________________________ (Bubbles, precipitate, sharp odor, bad odor, vinegar odor, temperature change, or no change) ii. A solution of potassium carbonate is mixed with a solution of hydrobromic acid. Net ionic equation, with phases ____________________________________ Accepted observation ____________________________________ (Bubbles, precipitate, sharp odor, bad odor, vinegar odor, temperature change, or no change) b. Fill in the blanks: When double displacement predicts the formation of HC2H3O2(aq), the accepted observation is _______________________________. When double displacement predicts the formation of NH4OH(aq), what really forms is ___________________________ and the accepted observation is ______________________. (3pts) Formula(s) Chem 400 Cosumnes River College Spring 2020 Lab Exam Professor Russell 7. EXPERIMENT 5 – THERMOCHEMISTRY Two reactions were performed in a calorimeter, using the same amounts and substances that we used in Experiment 5. Making the same assumptions we made for density and specific heat, calculate the experimental enthalpy changes, ∆H1 and ∆H2, in kJ/mol for Reactions 1 and 2 ONLY using the experimental data given below. (6pts) GIVEN INFORMATION AND DATA Reaction 1: (This is a net ionic equation, the molecular was ) Reaction 2: NH4 + (aq) + OH- (aq) à NH3(aq) + H2O(l) (This is a net ionic equation, the molecular was ) Summary of Results (even if your work is on scratch paper, restate answers here): ∆H1 : ___________________ ∆H2 : ___________________ Then using the results from Reactions 1 and 2, the experimental ∆H1 and ∆H2 you just calculated, and Hess’s Law, to determine ∆H3 (for Reaction 3 in our experiment): (The molecular equation for the above reaction is ) (3pts) ∆H3 : (via Hess Law)________________ Finally, calculate the percent error for your calculated ∆H3 , if the accepted value for ΔH3 is -52.97 kJ/mol. (3pts) ∆H3 percent error: __________________ END 2 (l) H (aq) + OH (aq) ® H O + - NaOH(aq) + HCl(aq) ® NaCl(aq) + H2O(l) NaOH NH Cl NH H O NaCl (aq) + 4 (aq) ® 3(aq) + 2 (l) + (aq) Reactions Reaction # 1 Reaction # 2 Reaction # 3 Max. Temp. (°C ) 41.6 27.6 Not given Initial. Temp. (°C ) 28.1 24.3 Not given Temp. Change (∆T,°C) 13.5 3.3 Not given (aq) 3(aq) 4 H (aq) NH NH + + + ® NH3(aq) + HCl(aq) ® NH4Cl(aq)