To prepare a standard solution of Mn 2+ a 0.250 g sample of Mn is dissolved in 1

Question

To prepare a standard solution of Mn2+ a 0.250 g sample of Mn is dissolved in 10 mL of concentrated HNO3 (measured with a graduated cylinder). The resulting solution is quantitatively transferred to a 100-mL volumetric fask and diluted to volume with distilled water. A 10 mL aliquot of the solution is pipeted into a 500-mL volumetric flask and diluted to volume.

(a) Express the concentration of Mn in mg/L, and estimate its uncertainty using a propagation of uncertainty.

(b) Can you improve the concentration’s uncertainty by using a pipet to measure the HNO3, instead of a graduated cylinder?

Explanation / Answer

a) The concentraion of first made 100ml solution is 0.025 g/L or 25mg/L

Now 10 ml of this solution is diluted to 500 ml.

Thus the concentration of resulting 500mL solution is 1mg/L

Since the nitric acid is measured in graduated cylinder, the amount of nitric acid can be more or less than the required 10mL, thus uncertainity in concentration is there.

By using a pipet nearly 90% of the uncertainity by using a graduated cylinder might have reduced.

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