AP/IB Chemistry: Acid Base Problems Name:
Acid Base Problems
1. A sodium hydroxide solution is standardized by titration with a pure sample of potassium hydrogen phthalate
(KHP – a monoprotic acid with a molecular mass of 204.22 grams). It takes 20.46 mL of an NaOH solution to titrate a 0.1082 gram sample of KHP. What is the molarity of the NaOH solution?
2. The effluent from an industrial process was analyzed and found to contain CCl4 and HC7H5O2 (benzoic acid). A sample of this effluent weighing 0.3518 grams was placed in water and shaken vigorously to dissolve the benzoic acid. The resulting solution required 10.59 mL of 0.1546 M NaOH for neutralization. Calculate the percent by mass of benzoic acid in the original sample.
3. In an experiment to determine the molecular weight for ascorbic acid, a monoprotic acid that can be represented by HA, a student dissolved 1.3717 grams of the acid in water to make 50.00 mL of solution. The entire solution was titrated with a 0.2211 M NaOH solution. It required 35.23 mL of the base to neutralize the acid. What is the molecular weight of ascorbic acid?
4. The percentage by weight of nitric acid, HNO3, in a sample of concentrated nitric acid is to be determined.
a. Initially, an NaOH solution was standardized by titration with a sample of KHC8H4O4, a monoprotic acid often used as a primary standard. A sample of KHC8H4O4 weighing 1.518 grams was dissolved in water and titrated with the NaOH solution. 26.90 mL of base was required. Calculate the molarity of the NaOH solution.
b. A 10.00 mL sample of concentrated HNO3 was diluted with water to a total volume of 500.0 mL. Then 25.00 mL of the diluted acid was titrated with the NaOH solution in part a. The equivalence point was reached after 28.35 mL of the base was added. Calculate the molarity of the concentrated solution.
5. The molecular mass of a monoprotic acid, HX, is to be determined. A 15.126 gram sample of HX was dissolved in distilled water so that the volume of the solution produced was 250.00 mL. Several 50.00 mL portions of this solution were titrated against an NaOH solution, requiring an average of 38.21 mL of NaOH. The NaOH was standardized against oxalic acid dihydrate, H2C2O4 • 2H2O (molecular mass 126.066 grams). The voume of NaOH solution required to neutralize 1.2596 grams of oxalic acid was 41.24 mL.
a. Calculate the molarity of the NaOH solution.
b. Calculate the molarity of HX in a 50.00 mL portion used for titration.
c. Calculate the molecular mass of HX.
6. A solution of hydrochloric acid has a density of 1.15 g/mL and is 30.0 % HCl by mass.
a. What is the molarity of the HCl solution?
b. What volume of this solution should be used in order to prepare 5.0 liters of 0.20 M HCl solution by dilution with water?
c. In order to obtain a precise concentration, the 0.20 M HCl is standardized against pure HgO (molecular mass 216.59 grams) by titrating the OH – produced according to the following reaction
HgO + 4I- + H2O HgI4–2 + 2OH-
In a typical experiment 0.7147 grams of HgO required 31.67 mL of the HCl solution for titration. Based on this data, what is the molarity of the HCl solution expressed to 4 significant figures?
7. A 0.500 liter sample of H2SO4 was analyzed by taking a 100.00 mL aliquot (portion) and adding 50.0 mL of
0.213 M NaOH. After the reaction occurred, an excess of OH- ions remained in the solution. The excess base required 13.21 mL of 0.103 M HCl for neutralization. Calculate the molarity of the original sample of H2SO4.
8. Oxalic acid, (COOH)2 or H2C2O4, is used to remove rust stains and some ink stains from fabrics. A 0.1743 gram sample of impure oxalic acid required 39.82 mL of 0.08915 M NaOH solution for complete neutralization. No acidic impurities were present. Calculate the % by mass of the oxalic acid in the sample.