Dilution : Dilute 1 mL of seawater (automatic pipet) to 100 mL; Have available a

Question

Dilution : Dilute 1 mL of seawater (automatic pipet) to 100 mL;

Have available a clean (but not necessarily dry) 50-mL beaker. Weigh it. Use an automatic pipet to take as much filtered seawater as you wish to dilute. Transfer the water to the beaker and weigh the beaker and its contents. Have available a clean (but not necessarily dry) 100-mL volumetric flask. Transfer quantitatively the seawater sample from the beaker to the volumetric flask. Use a plastic pipet and de-ionized water to rinse the entire sample in the beaker into the volumetric flask. Dilute the sample in the volumetric flask to the mark with filtered, de-ionized water.

By what factor have you diluted the seawater? Is diluting 4 mL of seawater to 100 mL reasonable?

Explanation / Answer

Firstly, you are allowed to take as much sea water as possible. Since you have a 50 mL beaker in which you take the sea water, let us assume that you filled the beaker upto the 50 mL mark with sea water. That is, you took 50 mL sea water. Now, you transfer this sea water quantitatively into the 100 mL volumetric flask and made upto the mark with filtered, de-ionized water. Since you had 50 mL sea water initially and you are having 100 mL sear water (after dilution) in the flask, you just diluted the sea water by a factor of 2, or in other words, the concentration of all the minerals present in sea water will be one-half after dilution. So, the dilution factor is 2.

Dilution experiments are carried out to ascertain concentrations of elements or compounds. The concentration of minerals, say like salt, is high in sea water, but the amount of salt present in 4 mL sea water is possibly quite less. If we dilute this 4 mL sea water to 100 mL, the concentration of salt will be much lower to do any reasonable experiment. Hence, to simply answer the second part, it is theoretically possible to dilute 4 mL of sea water to 100 mL, but the concentration of the minerals in sea water must be sufficiently high to work with the dilute solution.

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