Chromium in the Sauce

     As the local chemistry guru, you have asked by a local restaurant (Singer's Pub and Eatery) to see if there is any chromium in the special sauce he gives his customers. It seems as people have been eating his sauce and getting very sick. Nausea, gastrointestinal tract problems, etc. It seems Singer's is losing business from the bad rap is food is getting. He has seen the film 'Erin Brochovich' and thinks it might be chromium(VI) ion in his special sauce (which he buys wholesale).  

He gives you a sample of his special sauce and asks you to determine how much chromium +6 is in the sample. You do some research and find that dichromate ion has an LD50 = 190 mg/kg. Obviously being anywhere close to that is bad, as making you customers sick is one thing. It is completely different when you start knocking them off. Because no one has died yet, you conclude the concentration of chromium in the sauce is no more than 1000 mg/L (1000 ppm).

How are you to determine the concentration in the sauce? Solutions of dilute potassium dichromate are colored. You have access to a spectrometer, some accurate glassware, and some solid potassium dichromate. You need to make you own stock solutions and the concentrations will be calculated by you. This accuracy in this lab makes a difference, so you had better be very good with your volumes and masses. Mr. Singer does not want to look for a new sauce unless he has too, 

Before you make ANY solutions, you must show your calculation to your supervisor, to insure that you are not making a dangerous mistake.

The sauce has a bunch of stuff in it, but the tomatoes and solids have been filtered. There are lots of colors that remain in the system. You need to be confident that your color you are measuring comes from the chromium only.

The chromium in the sauce is just buried in the dichromate ion. The LD50 is net chromium +6 ion. For each chromate ion, there are 2 chromium ions.

The report consists of a formal PROFESSIONAL letter to the department of food safety. You will detail the procedure used to get a Beer's law data. You will give the appropriate graphs as well as the concentration in ppm of chromium in the sauce. Appropriate discussion is also required, as well as your standard critique.

Pre-lab questions (on a separate piece of recycled paper )

1. If you have a 50.00 mL volumetric flask, what mass of potassium dichromate should be put in the flask to make a stock solution of 4.00 x10-3 M.

2. How many solutions should you make? What range of absorbencies should your known solutions span?

3. Review the MSDS for potassium dichromate and give a brief overview of the hazards.

~MEO 02.26.04 16:15