You have a stock solution certified by a manufacturer to contain 160.0 ± 0.3 µg

Question

You have a stock solution certified by a manufacturer to contain 160.0 ± 0.3 µg SO42/mL. You would like to dilute it by a factor of 100 to obtain 1.600 µg/mL. Two possible methods of dilution are stated below. For each method, calculate the resulting uncertainty in concentration. Use manufacturer's tolerances in the Tolerances of Class A Volumetric Flasks table and Tolerances of Class A Transfer Pipets table for uncertainties.
(a) Dilute 10.00 mL up to 100 mL with a transfer pipet and volumetric flask. Then take 10.00 mL of the dilute solution and dilute it again to 100 mL.
(b) Dilute 1.000 mL up to 100 mL with a transfer pipet and volumetric flask.

Please calculate the resulting uncertainties in the concentration for each method.
(Class A) Tolerance for 100ml capacity volumetric flask = +/-0.08mL
(Class A) Tolerance for 10ml transfer pipet= +/-0.02mL

(c) Explain why one method is more precise than the other.
Method(a/b)is more precise because the uncertainty in the 10.00 mL transfer pipet is.....%and the uncertainty in the 1.000 mL transfer pipet is...%

Explanation / Answer

(a) on multiplication of any quantity the uncertainity adds

we will take 10mL of solution with 10mL transfer pipet with uncertainity =+/-0.02mL

so % uncertainity = 0.02 X 100/ 10 = 0.2%

Now we have used 100mL of volumetric flask for dilution, with uncertainity =+/-0.08mL

% uncertainity = 0.08 X 100/ 100 = 0.08%

Total uncertainity in measurement = 0.08 + 0.2 = 0.28%

Now we have again takne 10mL out of this with the use of 10mL pipette so the % uncertainity = 0.28 +0.2 = 0.48%

It is filled in 100mL so again % uncertainity =0.48 + 0.08 = 0.56%

b) now for second methode the unvertainity will be due to only the 100mL = 0.08% only

Method b is more precise because the uncetainity in the 10.00 mL transfer pipet is 0.56% %and the uncertainty in the 1.000 mL transfer pipet is 0.08%

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