Murder Investigation
Background: A crime has been committed and you, as a forensic detective, are going to use your knowledge of reactions, stoichiometry, and molarity to solve the crime. Miss Scarlet was found dead on the floor of the ballroom. Beside her body, police found a clear liquid solution that was used to kill her. Detectives were quick to determine that the solution was one of two chemicals. They knew Miss Scarlet was severely allergic to potassium iodide. Also, several members of the household used silver nitrate, which is also toxic if ingested. Police further discovered the following:
Professor Plum, an eccentric chemistry teacher, was working in the study with 0.250M silver nitrate solutions. Miss Scarlet was Prof. Plum’s worst student – arriving late to class late, breaking glassware, and rarely cleaning up after her experiments.
Mrs. White has a prescription for potassium iodide in her bathroom. Her pharmacist assures police that her potassium iodide solution has a molarity of 0.100M. Mrs. White was dating Miss Scarlet’s ex-boyfriend, which leads the police to suspect her.
Mr. Green, a photographer, had solutions of 0.100M silver nitrate solution in the darkroom. Compromising pictures of him with Miss Scarlet were found hidden in Scarlet’s bedroom. Police think the photos may be motive for murder as well.
Mrs. Peacock was found in the stable administering 0.250M potassium iodide solution to her horse. When questioned, she admitted that her horse has a severe case of bronchitis. It is likely that she knew of Miss Scarlet’s violent allergy to potassium iodide, since they had been lab partners in Professor Plum’s chemistry class.
Colonel Mustard had 0.30M silver nitrate solution in the conservatory. The Colonel enjoyed his leisure hours making explosives. The Colonel had been the assistant principal at the high school and was fired when Miss Scarlet overthrew the administration and took control of the school.
Your task: You have a sample of the murderer’s solution found at Miss Scarlet’s side. If you can determine whether it is silver nitrate or potassium iodide, then you can narrow the list of suspects considerably. Additionally, if you can determine the molarity of the unknown solution, then you can solve the case.
Who was the murderer? What was the murderer’s poison of choice? What was its molarity? Your evidence will be Exhibit A at the trial, and will be subjected to the scrutiny of the defense attorney. On the basis of your evidence, a murderer might be set free or an innocent person executed.
Materials Available:
15 mL of the suspect’s solutionwell plate beakerstirring rod
0.200M sodium chlorideflask funnel
0.100M sodium carbonatefilter paper balance
Data: Make a table that includes all data taken in the lab.
Calculations: Each calculation must start with a sentence explaining the purpose of the calculation, and all work must be shown. Include units
Conclusion:In a typed paragraph format, summarize your procedures, and state who you suspect the murderer is based on your evidence/data. Discuss 3 possible sources of errors and their effects on your results.
Things to consider (for procedures):
Part A: Determining the Solution
1.What are the chemicals available to you?
2.What kind of reactions can you produce with the chemicals available?
3.How can you determine the solution used from the results?
Part B: Determining the Molarity
1.How will you collect the precipitate? What data will you need to collect?
a.LABEL the filter paper WITH YOUR NAME
b.WEIGH the filter paper
2.Which chemical reaction do you choose?
3.If you are only allowed to use up to 15 mL of the poison, how much of the solution will you need to use for each suspect?
4.What amount will guarantee that all the poison will react with the solution? (So think about your excess and limiting reactants.)