Los Angeles City College Chemistry 60
EXPERIMENT 17: ACID-BASE REACTIONS AND TITRATION
Introduction: This experiment demonstrates the analytical technique, titration. In a
titration, a solution is delivered from a burette until it completely consumes another solution in a
flask. You will chemically react an acid with a base, until the endpoint of the reaction is shown
by the indicator phenolphthalein. You will first determine the concentration of a base solution
(standardization) and then of an unknown acid solution using previously standardized base.
The reaction of a strong acid and a strong base goes quickly: i.e.
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
acid base salt water
This reaction is often called neutralization.
Part A: To standardize the NaOH solution, we will react it with potassium hydrogen phthalate,
KHC8H4O4 Because of its complex formula, this compound is often called “KHP”. The molar
mass of KHP is 204.2 grams per mole.
KHC8H4O4(aq) + NaOH(aq) KNaC8H4O4(aq) + H2O(l)
Starting with a known mass of KHP then recording the volume of NaOH needed to reach the
endpoint, we can calculate the molarity of the base .We want the titrated solution to be a very
pale pink, not bright rosy red, at the endpoint.
Part B: Once the concentration of the NaOH solution in the buret is known, we can determine
the concentration of an HCl solution by titrating it with the NaOH solution from part A.
Phenolphthalein is used as the indicator by adding it to the HCl solution.
Materials needed:
Chemicals
Equipment
Solid KHC
8
H
4
O
4
(“KHP”)
Deionized water
Phenolphthalein solution
Approximately 0.2M NaOH solution
Unknown HCl solution
Weighing vial , scoop or spatula
3 125-mL Erlenmeyer flasks or 2 flasks and a 250
mL beaker
wash bottle with deionized water.
50-mL buret, buret holder and ring stand
Plastic funnel. 500-mL florence flask
Procedure:
Part A: Standardization of an unknown base
1. Obtain and rinse a burette with deionized water from your wash bottle. CAUTION: do
not stick the end of the burette under the faucet! It
leaks all over the floor. Be sure to open the valve at the
bottom and let some water rinse out the stopcock. If
you think the tip is clogged, ask your instructor to
check it.
2. Practice reading the meniscus in your burette while
cleaning it with deionized water. Read your burette by
estimating between the 0.1-mL marks. In other words,
your recorded volume measurements include an uncertain digit at 0.01 mL. If the
meniscus is right on a mark, record the second decimal place as a zero. Hold the clean
burette in the burette clamp that is attached to the ring stand.
3. Obtain a 500 mL Florence flask, clean it well with deionized water, and then pour
approximately 16-17 mL of 6 M NaOH. Ask your instructor which bottle of sodium
