160 g of a 0.80% sodium hydroxide solution.
The following question involves the reaction of sodium hydroxideand succinic acid. Succinic acid is diprotic: the acid(H2C4H4O4) reacts withtwo of its hydrogens to giveC4H4O42-. The balanced“molecular†equation for the reaction has coefficients of 2 forNaOH and 1 for succinic acid:
2 NaOH (aq) +H2C4H4O4 (aq) -->Na2C4H4O4 (aq) + 2H2O (l)
A student weighs 1.700 g of succinic acid and dissolves it inwater in a 250.0 mL volumetric flask. A 25.00 mL sample of thissolution is withdrawn and placed in a 125 mL Erlenmeyer flask, towhich 5 drops of the acid-base indicator phenolphthalein is added.This solution is titrated with a sodium hydroxide solution ofunknown molarity in a buret.
a) How many moles of succinic acid were weighed and dissolved inthe volumetric flask?
0.0572 M
b) How many moles of succinic acid were placed in the Erlenmeyerflask?
1.43 x 10-3 mol
c) If the unknown sodium hydroxide solution was known to beapproximately 0.20 M, at approximately what buret volume would youexpect the end point of the titration? Show the calculation,including the use of the appropriate coefficients, as a 2significant figure estimate:
14.30 mL NaOH
d) If the measured volume at the end point was 13.32 mL ofsodium hydroxide added, calculate the actual molarity of the sodiumhydroxide solution.
0.214 M NaOH
You are going to standardize a 0.80% solution of sodiumhydroxide solution for which the molarity is approximately 0.20 M.You will have dry succinic acid, a 250 mL volumetric flask, a 25.00mL pipet, a 50.00 mL buret, a phenolphthalein indicator solution,and other standard laboratory equipment. For each titration youwill withdraw a 25.00 mL sample of the succinic acid solution witha volumetric pipet. Therefore, you will deliver exactly one-tenthof your initial mass of succinic acid (to four significant figures)in each titration. In deciding the amount of succinic acid toweigh, assume that you will be using approximately 15 mL of thesodium hydroxide of approximate 0.20 M concentration for eachtitration, and you need enough succinic acid for ten titrations.Show how to calculate the mass of succinic acid you willneed to weigh.
