8. Consider the following hypothetical reaction A titration was performed in whi

Question

8. Consider the following hypothetical reaction A titration was performed in which a standardized solution of A was used as the titrant, and an unknown amount of B was the analyte. The concentration of A in the standardized solution was 0.2105 M (relative uncertainty 0.4%). The initial buret reading was 4.45 mL, and the final buret reading (at the endpoint) was 42.06 mL A) How many moles of B were present in the unknown sample? B) If the absolute uncertainty of the total volume delivered from the buret is ±0.05 mL, what is the absolute uncertainty associated with your answer to part A?

Explanation / Answer

A)
Final reading - initial reading = 42.06mL- 4.45mL = 37.61 mL/1000 = 0.03761 L
moles of B in the sample,m = 0.2105 mol/L * 0.03761L = 7.9169*10-3
u(m) / m = [ (u(C)/C)2 ]1/2
u(m) = [ (0.04 / 0.2105)2]1/2 * 7.9165*10-3 = 1.50432*10-3
moles of B in sample = (7.9169*10-3 ± 1.50432*10-3) mol

B) u(m)/m = [ (u(C)/C)2 + (u(v)/v)2 ]1/2
u(m) = [ (0.04/0.2105)2 + (5*10-5L / 0.03761)2]1/2 * 7.9165*10-3 = 1.50435*10-3 mol
moles of B in sample with uncertainity in volume = (7.9169*10-3 ± 1.50435*10-3) mol

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