Question

A solution of HNO3 is standardized by reaction with pure sodium carbonate.

A volume of 24.70 ± 0.05 mL of HNO3 solution was required for complete reaction with 0.9746 ± 0.0008 g of Na2CO3, (FM 105.988 ± 0.001). Find the molarity of the HNO3 and its absolute uncertainty.

Answer 1

Work the problem once with the values that cause the largest answer:
( 0.9754 g Na2CO3) / (105.987 g Na2CO3/mol) x (2 mol HNO3 / 1 mol Na2CO3) / (0.02465 L HNO3) = 0.746694967 mol/L HNO3

Work the problem again with the values that cause the smallest answer:
( 0.9738 g Na2CO3) / (105.989 g Na2CO3/mol) x (2 mol HNO3 / 1 mol Na2CO3) / (0.02475 L HNO3) = 0.742444113 mol/L HNO3

Find the average of the two answers:
(0.746694967 + 0.742444113) / 2 = 0.74456954

Find the uncertainty:
(0.746694967 - 0.742444113) / 2 = 0.002125

So the answer is:
0.744 ± 0.002 mol/L HNO3