Precision and accuracy of a solution

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Discussion Overview

The discussion revolves around the precision and accuracy of a diluted solution in a chemistry context, specifically focusing on how to mathematically calculate the precision after performing a dilution. Participants explore the implications of relative uncertainty and the effects of measurement inaccuracies.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a dilution scenario and seeks to calculate the precision of the resulting solution mathematically.
  • Another participant asserts that the relative uncertainty remains constant, but additional uncertainty may arise from inaccuracies in measuring the 5 mL and 100 mL volumes.
  • A participant questions whether the precision remains the same for all diluted solutions, suggesting it would be ±0.01 for all cases.
  • It is noted that the relative uncertainty is approximately 1/40, indicating that the concentration could vary by that factor, regardless of subsequent dilutions.
  • One participant proposes that the final result could be expressed as 8*10^-5 ±1/40, while another challenges this by stating it should be 8*10^-5 ±2*10^-6, emphasizing the uncertainty derived from the dilution factor.
  • Concerns are raised about the exactness of the 5 mL and 100 mL measurements, which could introduce additional errors.
  • A reference to external resources on volumetric glassware tolerances is provided for further context.

Areas of Agreement / Disagreement

Participants express differing views on how to calculate and interpret the precision of the diluted solution. There is no consensus on the final expression of uncertainty or the implications of dilution on precision.

Contextual Notes

Participants acknowledge potential inaccuracies in measuring volumes, which could affect the overall precision of the solution. The discussion reflects varying interpretations of how dilution impacts uncertainty and the mathematical representation of that uncertainty.

cham
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Homework Statement


so let's say that we have a solution S=0.4±0.01/250ml
i want to do a dilution
so i pick 5ml and pour it into 100ml beaker
how should i calculate precision of the solution (mathematically or with some other equations)?

Homework Equations


so basically we have F=5*S/100

The Attempt at a Solution


for me 5*S/100=8*10^-5±2*10^-6
is this true because it doesn't seem right for me (about the pricision)?
 
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The relative uncertainty stays the same, that is right.
You might get an additional uncertainty if the 5ml or the 100ml are not exact.
 
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so
mfb said:
The relative uncertainty stays the same, that is right.
You might get an additional uncertainty if the 5ml or the 100ml are not exact.
so what you say is that no mater how many dilution we do the precision stays the same and it depends on the solution we're using.so it means ±0.01 for all diluted solutions we made,right?
 
The relative uncertainty stays the same.
It is always 1/40. Roughly speaking, your solution might be 1/40 more concentrated than you thought, or 1/40 less. And that uncertainty does not change if your dilution factors afterwards are known exactly.
 
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so let's assume that final result is true , so it would be 8*10^-5 ±1/40 and so for all resulting solutions
and that by using Δy/y
correct me if I'm wrong
thanks and sorry for my stubbornness
 
I am afraid you can be sure neither 5 mL nor 100 mL are exact and they are additional sources of error.
 
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cham said:
so let's assume that final result is true , so it would be 8*10^-5 ±1/40 and so for all resulting solutions
No, in this case it would be 8*10-5 +- 2*10-6 as the uncertainty is 1/40 of the value.

With the caveat that the 5ml and 100ml won't be exact, as mentioned.
 
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thank you mfb and Borek for your help
much appreciated
 
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You can use @cham to tag users in the thread.
 
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