Analytical chem lab and dilution factors

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Discussion Overview

The discussion revolves around calculating the amount of iron (Fe) in a vitamin pill based on a series of dilutions and absorbance measurements. Participants are exploring the implications of dilution factors and the correct application of concentration equations in a laboratory context.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • The initial calculation presented by the first participant suggests that the amount of Fe in the tablet is 48.0 mg, but they express uncertainty about whether to account for the initial dilution of 25 mL HCl to 250 mL.
  • Another participant outlines the dilution steps, indicating that the stock solution A is 40 times stronger than the final sample solution, which contains 12.0 mg/L of iron.
  • One participant, chemisttree, proposes that if the sample solution is 40 times weaker, then the iron content in the tablet could be calculated as 4.8 mg based on the concentration of the sample solution and the volume pipetted.
  • There is a challenge to the correctness of the calculations, with a focus on the importance of understanding the dilution steps and how they affect the final concentration of iron in the sample solution.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct amount of iron in the tablet, as there are competing calculations and interpretations of the dilution process. The discussion remains unresolved regarding the correct application of the dilution factors and the resulting calculations.

Contextual Notes

Participants highlight the need to clarify the significance of each dilution step and how it impacts the final concentration, indicating potential gaps in understanding the relationship between the dilutions and the final calculations.

tarzanna
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Homework Statement


Find the mg of Fe in vitamin pill. Vitamin pill was dissolved in 25mL HCl which was then diluted to 250mL with water in flask. 25mL of that solution was then diluted to 100mL in another flask. 10mL of the second was diluted to 100mL in another flask. Absorbance of the last solution and standard solutions were taken and a calibration curve created. It was determined that the sample solution contained 12.0mg/L iron. Determine the number of mg of Fe in tablet.

Homework Equations


The Attempt at a Solution



12.0mg/L x 0.100L x (100mL/25mL) x (100mL/10mL)=48.0mg Fe in tablet

I am not sure if I am correct. Do I need to account for the 25mL HCl diluted to 250mL as well?

Any help in direction would be greatly appreciated! Thanks.
 
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25 mL (whole sample) ---> 250 mL Stock solution A

Stock solution A (25 mL) -----> 100 mL Stock solution B (1/4 as strong as A)

Stock solution B (10 mL) -----> 100 mL Sample solution (1/10 as strong as B)

Can you get there from here?
(your answer is not correct)
 
chemisttree: So, the original solution is 40x stronger than the sample solution. So if the sample solution contains 12.0 mg/L and total volume pipetted was 10 mL , is this the iron content of the tablet?

12.0 mg/L x 40 = 480 mg/L x 0.010L = 4.8 mg

Is this correct?

Thanks!
 
tarzanna said:
chemisttree: So, the original solution is 40x stronger than the sample solution. So if the sample solution contains 12.0 mg/L and total volume pipetted was 10 mL , is this the iron content of the tablet?

12.0 mg/L x 40 = 480 mg/L x 0.010L = 4.8 mg

Is this correct?

Thanks!

Not yet!

Here is where you went wrong with your logic...
...and total volume pipetted was 10 mL ,...
Why is it important to know how much was pipetted from Stock solution B to the final Sample solution? You already used that information to determine that the Sample solution is 1/40 th as strong as the original solution which has the tablet's entire contents.
 

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