You are the boss of a commercial analytical laboratory and your job is to check

Question

You are the boss of a commercial analytical laboratory and your job is to check all results before they are sent to the customers. One day you look at the numbers from the analysis of benzene in BTEX contaminated groundwater samples. For a given sample, your laboratory reports a benzene concentration in water of 100 micrograms/L.

Knowing the problems associated with the analysis of volatile organic compounds, you inquire about the handling of the samples. Here we go! The samples (100 mL) were put into 1 L flasks, which were then sealed and stored at 5°C for several days. Then, in the cooling room, an aliquot of the water was withdrawn and analyzed for benzene. What was the original concentration of benzene in the water sample? Assume that equilibrium is established between the gas phase and the water and neglect adsorption of benzene to the glass walls of the bottle. The data required to answer this question can be found in Table 3.4.

Explanation / Answer

Answer: Here we have given that the initially we have 100 microgram/L means 100 * 10-6 gram per L

means 1000 ml contain = 10-4 gram

and , Hence the 100 ml contains = 10-4 * 100/1000 = 10-5 gram benzene

Now the concentration of Benzene is = 10-5/ 78.11 = 0.128 microM

hence the required concentration is 0.128 microM .

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