You have a standard solution of an amino acid which is certified by the manufact

Question

You have a standard solution of an amino acid which is certified by the manufacturer to contain 184.7 mol/mL (±0.3) . You would like to dilute it by a factor of 100. Two possible methods of dilution are available. One of these methods is less precise than the other. For each method calculate the resulting percent relative uncertainty in concentration, and ONLY enter the percent relative uncertainty of the method which is less precise. a) Dilute 10.00 (±0.02) mL of the standard solution up to 100.00 (±0.08) mL with a transfer pipet and volumetric flask. Then take 10.00 (±0.02) mL of the dilute solution and dilute it again to 100.00 ( ±0.08) mL. b) Dilute 1.000 (±0.006) mL of the standard solution up to 100.00 (±0.08) mL with a transfer pipet and volumetric flask.

Explanation / Answer

a) The relative uncertainty in the transfer pipette is (0.02 mL)/(10 mL) = 0.002.

The percent relative uncertainty in the volumetric flask is (0.08 mL)/(100 mL) = 0.0008.

Since, we perform both the operations twice, the relative uncertainty of this method =

The percent relative uncertainty of the first method is given as (3.046*10-3)*100% = 0.3046% (ans).

b) The relative uncertainty in the transfer pipette = (0.006 mL)/(1.000 mL) = 0.006.

The relative uncertainty in the volumetric flask = (0.08 mL)/(100 mL) = 0.0008.

The relative uncertainty in this method =

The percent relative uncertainty in this method = (6.053*10-3)*100% = 0.6053%.

Method (b) has a higher value of the percent relative uncertainty and is therefore, less precise.

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