Suppose a 4.272 g soil sample undergoes an extraction with 50 ml of extracting solvent to remove the lead. This 50 ml was then diluted to 250 ml and tested by atomic absorption technique. The concentration of lead in this diluted extract was found to be 35.7 ppm. What is the lead concentration, in ppm, in the untreated soil sample?

Question

Suppose a 4.272 g soil sample undergoes an extraction with 50 ml of extracting solvent to remove the lead. This 50 ml was then diluted to 250 ml and tested by atomic absorption technique. The concentration of lead in this diluted extract was found to be 35.7 ppm. What is the lead concentration, in ppm, in the untreated soil sample?

Is this as simple as 35.7 ppm x 5 times dillution = 187.5 ppm?

Answer 1

Yes but you didn't multiply right. (rather, I think you transposed the numbers)

Answer 2

Thanks so much. You are correct the answer should read 178.5 ppm.

Answer 3

Could someone please clarify. I recently sent this question to the forum and thought I had it figured out. Now another student has told me to do this:

35.7 ppm x 250ml = 8.925 x 10-3 g
8.925 x 10-3 g/4.272g=2.089 x 10-3 = 2089 x 10-6 = 2089ppm

Please help I do not know what is the correct way of completing this question.

Answer 4

To calculate the lead concentration in the untreated soil sample, it is important to take into account the dilution factor, as well as the initial mass of the soil sample.

First, we need to determine the amount of lead that was extracted from the soil sample. Since the soil sample weighs 4.272 g, we assume that the entire mass of lead in the sample was extracted.

Next, we need to calculate the concentration of lead in the extract solution after the initial extraction. This can be done using the formula:

Concentration of lead in the extract = (mass of lead extracted / volume of extract solution)

Substituting the values, with the mass of lead extracted being equal to the mass of the soil sample (4.272 g) and the volume of the extract solution being 50 ml, we can calculate the concentration of lead in the extract.

Concentration of lead in the extract = (4.272 g / 50 ml)

Now, we need to consider the dilution factor. The diluted extract was made by diluting the original extract solution to a final volume of 250 ml using an appropriate solvent. This means that the diluted extract is 5 times more dilute than the initial extract, or has a dilution factor of 1/5.

To find the lead concentration in the diluted extract, we multiply the concentration of lead in the initial extract by the dilution factor:

Concentration of lead in the diluted extract = (concentration of lead in the extract x dilution factor)

Finally, to find the lead concentration in the untreated soil sample, we multiply the concentration of lead in the diluted extract by the dilution factor:

Lead concentration in the untreated soil sample = (concentration of lead in the diluted extract x dilution factor)

Therefore, the correct calculation would be:

Lead concentration in the untreated soil sample = (35.7 ppm x 1/5)

This gives the lead concentration in the untreated soil sample, taking into account the dilution and extraction processes.