This is a fairly simple undergraduate level (if not high school) stochiometry problem. There are plenty of online calculators you can google for this.

Convert the ppm to ug/ml for a start: 1500 µg per ml.

1500 µg/ml x 1ml / 250 ml = 1500/250 = 6 µg/ml

dilution factor (DF) is 250x.

Are you asking about the total dilution from the original sample?

25 ml / 0.500 g = 50x,

followed by 250 ml /1ml = 250 x 50 = 12500x DF

Double checking: 1500 µg/ml * 25 ml = 37500 µg Pb from 0.5g of sample

divide by 0.5 both sides = 75000 µg in 1 g sample

diluting by 12500x dilution factor = 75000 µg / 12500 ml

assuming 1 g is equivalent to 1 ml = 6 µ/ml

Did you get a different value?

The dilution factor when 1 mL of a 1500 ppm Pb solution is diluted to 250 mL is 250. To find lead concentration by UV-Vis, form a colored Pb complex, measure its absorbance, use a calibration curve from standards, and account for any dilution.

Hi! You've described your problem very vaguely, and it's hard to guess what you might be referring to. Below are my comments.

1. The fact that the measurement technique used was or is intended to be UV-VIS spectrometry (not spectroscopy) is irrelevant. Your problem doesn't concern the measurement technique itself, but rather elementary calculations in chemical analysis.

2. A 500 mg test portion of a sample, presumably solid, containing Pb was weighed. After preparation, the solution was diluted to 25 mL. The Pb concentration in this diluted solution was reported to be 1500 ppm. How much is this? We assume it's 1500 mg/L, not 1500 mg/kg.

3. Using the symbol "ppm" instead of "mg/L" is incorrect. Because a concentration of 1500 mg/L will only be a concentration of 1500 mg/kg if the solution density is exactly 1 g/mL (1 kg/L), which is usually significantly different from 1 g/mL. This "ppm" is just a proportion, like %, ‰, ppb, etc.

3. This information about a Pb concentration of 1500 mg/L should be confirmed using a different measurement technique, but in a much more dilute solution, namely one diluted 250 times.

4. Let's assume that the measurement has already been performed and the result is a Pb concentration exactly 250 times lower than the concentration in the concentrated solution. This means the result is 1500 mg/L / 250 = 6 mg/L.

5. But your problem isn't the dilution factor, but how to calculate the Pb concentration in the analyzed sample.

6. For samples (solid or liquid) from which appropriate test portions are weighed for analysis, it is best to first calculate the "sample concentrations" in the solutions being measured, instead of using abstract multipliers. This is regardless of whether the samples were completely or only partially dissolved.

7. In our case, 500 mg in 25 mL is 20 g/L. And after an additional 250-fold dilution, this is 80 mg/L.

8. In this "sample" solution (80 mg/L), the Pb concentration was measured and was 6 mg/L.

9. The Pb content in the sample is therefore:

6 mg/L / 80 mg/L = 0.0750 = 7.50%

Best regards!

ZJ

Hi,

You may use the web tool to calculate

https://www.alfa-chemistry.com/solution-dilution-calculator.htm

https://www.alfa-chemistry.com/mass-molarity-calculator.htm

Dilution Factor = 250

Pb present in 500mg

sample = 37.5

mg