Using Molarity to Solve a Crime

Using Molarity to Solve a Crime

Braxton Larsen

May 22, 2017

Introduction

Molarity is defined as a concentration unit, defined to be the number of moles of solute divided by the number of liters of solution. Throughout this lab, molarity will be used to determine the murderer of Fred Flintstone. The overall purpose of this lab is to use molarity to figure out which substance was used to murder Fred Flintstone. Each person on the suspect list had access to either potassium iodide or silver nitrate, and the molarities of their substances were given. In order to figure which of the two murder weapons was used, tests of each of the substances in a salt solution would need to be done. The solution(s)  that react(s) can be defined as the murder weapon. As a result of figuring out what the murder weapon is,  this will help limit the number of suspects for the murder down to three people. The scientific concepts being investigated are double replacement reactions as well as molarity of solutions.  

Methods

Materials

• 0.1  M aqueous sodium chloride
• 0.1  M aqueous sodium carbonate
• Well plate
• Sample of each possible murder weapon
• Magnifying glass
• Medicine droppers
• 50 mL flask
• Hot plate
• Tongs  
• Graduated cylinder/pipet
• 20 mL of .1 M sodium chloride
• 10 mL sample of murder weapon(#  )
• Balance

Procedure

Put on Safety goggles. Perform each of the reactions by combining three drops of each of the reactants in one of the wells on the well plate. Repeat for the remaining three substances. Record your results and observations.  (Day 1)

Put on safety goggles. Weigh the empty flask or beaker and record the mass. Use a graduated cylinder, and measure out 20 mL of sodium chloride. Place the sodium chloride in the flask. Clean graduated cylinder thoroughly. Then use a graduated cylinder, to measure out 10 mL of murder weapon and add to the flask.  Heat the flask on a hot plate on the highest setting until the liquid is fully evaporated. Turn down the heat when the liquid is bubbling/popping.  Then measure the mass of the flask and the powder that is remaining and record in table. Subtract to find the mass of the powder and record results. (Day 3)

Observations and Data

Analysis of Data

When testing in science, there are many sources of error or variations that could occur. Throughout the lab, many things could have been changed. On day two of experimenting, the measurements for the two solutions were not measured very accurately, as an effect this could have caused the substances to not produce as much salt. Another source of error could have occurred when using a balance to mass the flask. Not massing the flask correctly could affect your mass at the end when you are required to subtract the substance’s mass from the flask’s original mass. One other source of error on day occurred when the two solutions in the flask were finishing boiling, many particles began popping out. This happened due to the heat not being turned down quick enough. As a result of this occurring, the overall mass as well as the molarity would be completely different. Another margin of error could have occurred if the flasks were not washed/cleaned thoroughly. If the flasks contain particles from past experiments, the amount of salt as well as the molarity may be different. It was also difficult to completly boil all of the water out of the solution, because the droplets were condensing on the side during the experiment, this would also affect the mass and the molarity of the solution. If all of these factors/variations were changed the results would have been much more accurate and precise.