Question

A chemist is determining the molarity of unknown acid by adding enough base with a buret to reach the equivalence point. The initial buret reading that contained the NaOH was 3.45 mL (+/- 0.02 mL) and the final reading was 28.91 mL (+/- 0.02 mL)   The molarity of the base was labeled as 0.078 M (+/- 0.0004). How many moles of base were added to the flask, report to the correct answer as indicated by absolute uncertainty.

Answer 1

NaOH volume used = 28.91 -3.45 ) +- ( 0.02+0.02) = 25.46 ( +/-0.04)

we find % uncertainity , 0.04 = 25.46 x ( X/100) , X = 0.157 %

Thus NaOH = 25.46 +/- 0.157 %   = 0.02546 L + /- 0.157 %

Molarity = 0.078 ( + /0.0004)

0.0004 = 0.078 x ( X/100) , X = 0.5128

Thus Molarity = ( 0.078 +/- 0.5128 %)

Now Moles = Molarity x volume in L  

              = ( 0.078+/-0.5128) x ( 0.02546+/-0.157)

              = 0.078x0.02546) +/- ( 0.5128+0.157)

                = 0.001986 + /- 0.67%

0.67 % of 0.001986 = 0.0000133

Thus moles = 0.001986 +/- 0.0000133