4.3.1 Acid-Base Titrations

Question 1

Acid-Base Titrations

Answer 1

• Titration is used to determine the number of moles of an unknown by adding a known amount of reagent that reacts with the unknown stoichiometrically.
• An acid-base titration involves the addition of a known volume of a basic (or acidic) substance of known concentration to a known volume of an acidic (or basic) solution of unknown concentration

Question 2

oxidation-reduction reactions

Answer 2

• Titration is the method used to determine the number of moles of an unknown by adding a known amount of reagent that reacts with the unknown stoichiometrically.
• Titrations can involve acid-base reactions and oxidation-reduction reactions.

Question 3

note

Answer 3

• An acid-base titration involves the addition of a known volume of a basic (or acidic) substance of known concentration to a known volume of an acidic (or basic) solution of unknown concentration.
• In an acid-base titration an indicator is employed that changes color when the equivalence pointis reached for the titration. This equivalence point is reached when the acid (or base) completely neutralizes the base (or acid) of the sample.
• In the example, to determine the unknown amount of oxalic acid in the sample, it is titrated with a known volume (34.47 mL) of a basic solution (NaOH) of a known concentration (0.485 M).
• For the calculations it is important to recognize that oxalic acid is a diprotic acid, one mole of acid can neutralize two moles of base.
• The purity of the oxalic acid sample is determined (the amount of oxalic acid divided by the amount of the total sample) by converting the volume of NaOH titrated into moles of hydroxide ion.
• Moles of hydroxide ion are converted into moles of oxalic acid using the 2:1 ratio for a diprotic acid.
• The molar mass of oxalic acid is used to convert the moles of oxalic acid into mass and the percent purity of the sample is estimated by dividing the mass of oxalic acid by the mass of the total sample and multiplying by 100.
• In this problem, the is assumed not to be an acid.

Question 4

A 0.0680 M solution of KOH is used to titrate 42.3 mL of H3PO4, a triprotic acid. The initial reading of the buret is 61.7 mL, and the final reading is 12.4 mL. What is the molar concentration of the H3PO4 solution?

Answer 4

0.0265 M

Question 5

Why couldn’t a 0.22 M solution of ammonia (NH3 ) be titrated with a 0.22 M solution of sodium hydroxide (NaOH)?

Answer 5

Sodium hydroxide is incapable of neutralizing ammonia, since both are bases.

Question 6

How many milliliters of a 0.208 M solution of NaOH will it take to titrate 7.34 mL of a 0.820 M solution of HBr?

Answer 6

28.9 mL

Question 7

It takes 34.3 mL of a 0.398 M solution of HClO3 to titrate 40.0 mL of a solution of Mg(OH)2. How many grams of magnesium does the titrated solution contain?

Answer 7

0.166g

Question 8

Potassium hydrogen phthalate (KHP) is a weak monoprotic acid with a molar mass of 204.20 g / mol. An impure sample of KHP has a mass of 2.45 g. (Note: only the KHP portion of the sample actually reacts with NaOH in the titration.) It takes 34.8 mL of a 0.200 M solution of NaOH to titrate the impure sample when it is dissolved in water. How many grams of impurities does the sample contain?

Answer 8

1.03 g

Question 9

The active ingredient in some types of antacid tablets is CaCO3. It neutralizes stomach acid (HCl) according to the following reaction.

CaCO3(s) + 2H + + 2Cl − → H2O + CO2 + Ca2+ + 2Cl −

You crush an antacid tablet with a mass of 0.730 g, and then titrate it with 47.0 mL of 0.235 M HCl. What is the percent by mass of CaCO3 in the antacid tablet? (assuming that no other bases are present)

Answer 9

75.6%

Question 10

An impure sample of NaOH has a mass of 0.821 g. It takes 114 mL of a 0.0861 M solution of HCl to titrate this sample. What is the percentage of purity of the NaOH sample?

Answer 10

47.9%

Question 11

The solute in an acidic solution is an impure sample of oxalic acid (a diprotic acid). This solution is titrated with 49.8 mL of a 0.145 M solution of NaOH. What other piece of information will allow you to calculate the molar concentration of oxalic acid in the acidic solution?

Answer 11

the volume of the acidic solution

Question 12

It takes 52.6 mL of a 0.724 M solution of potassium hydroxide (KOH) to titrate 86.8 mL of a solution of nitric acid (HNO3 ). What is the molar concentration of the nitric acid solution?

Answer 12

0.439 M

Question 13

Which of these titrations will require the greatest volume of base to reach the last equivalence point?

Answer 13

50 mL of 0.01 M, phosphoric acid, H3PO4 titrated with 0.01 M KOH