How much cobalt is in the soil?
A group of local dairy farmers has recently reported to the county that their animals appear sick. Based on the symptoms, the county suspects the cows are suffering from cobalt deficiency. As you remember from last semester, Cobalt (II) is required for production of vitamin B12. Proper animal diet requires the soil to contain 0.13 to 0.30 mg cobalt per kg/soil. Soils below this level can be treated with cobalt nitrate or other cobalt solutions. Because the county does not have the technology, they hire you to determine the amount of cobalt in a sample of soil they have sent to you.
To get representative samples, the extension service collected 2.00 kg of soil from several different farms in the county. The cobalt from each sample was extracted from the soil, dissolved in water, and concentrated by a factor of 10,000 to final V of 500 mL. The average density of the soil is 0.33 g/mL Because the cobalt ion is a colored species in water, you can use your handy-dandy spectrometer to determine the concentration of the solution.
You will need to make a standard Beer's Law plot of known solutions (A concentrated standard solution will be given too you, whose concentration is ~0.3 M in Co2+) You must determine the amount of cobalt (if any) needs to be added to the soil. The farmers are not very good at math, so you will have to determine how much cobalt nitrate needs to be added per acre of farmland. Assume the depth of the 'soil' is 1 foot. You will need to know what the mass of a volume of soil is 1 acre in area and 1 foot in thickness.
You report will be a short form memo. Don't forget the lab critique, either.
You might find it beneficial to review the lab from last semester, color in soda to recall how to do this sortof lab. Look closely at the lab picture, that will help.
Prelab Questions (worth 5 points) (Where should I write them??)
1.What is the volume of a space 1 acre in area x 1 foot in depth. SI units, of course.
2. If you determine the concentration of the of one farms sample is 0.15 M, how many mg of Co are in each kg of soil? It is just a unit conversion problem, remember the concentrated part (x 10,000)
3. Write up (and show the instructor on your way in) some semblance of a procedure and data sheet.