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Titration Experiment: Molarity and pH Determination
Objective: To become familiar with titration and determine the molarity and pH of an acid solution.
Introduction
An Arrhenius acid ionizes in water to produce hydronium ions (H₃O⁺) and an Arrhenius base produces hydroxide ions (OH⁻) in water.
According to the Bronsted-Lowry concept, an acid is a proton donor and a base is a proton acceptor.
A neutralization reaction occurs when an acid reacts with a base to produce water. In this experiment, we will perform a neutralization to standardize the solution. Standardization is the process of determining the exact concentration of a solution.
Titration is the technique used to measure the volume of a solution required to react with another. An indicator solution is used to detect the endpoint, which is indicated by a color change. For instance, Phenolphthalein changes from colorless to pink at a pH of 9.
The equivalent point is the point at which stoichiometrically equal quantities of acid and base react.
The relationship between molarity and pH is important for determining the acidity of solutions. Molarity (M) is the number of moles per liter of solution. pH is defined as the negative logarithm of the hydronium ion concentration.
Reaction
NaOH + HCl → NaCl + H₂O
Apparatus
- 600mL Beaker
- 250mL Erlenmeyer Flask
- Ring Stand
- Buret Clamp
- Electronic Balance
- 50mL Burette
- 500mL Erlenmeyer Flask
- Wash Bottle
Chemicals
- Sodium Hydroxide (NaOH)
- Hydrochloric Acid (HCl)
- Phenolphthalein Solution
Procedure
Part A: Standardization of NaOH Solution
- Fill the burette with NaOH and ensure no air bubbles. The lower meniscus should be at zero.
- Add 10mL of HCl to an Erlenmeyer flask and add a few drops of phenolphthalein solution.
- Gradually add NaOH to the flask. The solution will begin to turn pink as the NaOH is added.
- Continue adding NaOH until the solution remains pink, indicating the endpoint has been reached.
- Record the volume of NaOH used.
- Repeat the procedure 3-4 times to obtain concordant readings.
- Calculate the molarity of NaOH using the recorded data.
Part B: Analysis of Unknown Acid
- Obtain 10mL of the unknown solution.
- Repeat the titration process as in Part A to determine the molarity of the unknown acid.
Observations and Calculations
Part A:
- Molarity of HCl: MA = ________
- Volume of HCl used: VA = ________
- Molarity of NaOH: MB = ________
- Volume of NaOH used: VB = ________
- Formula: MA × VA = MB × VB
Part B:
- Volume of Unknown Acid: VA = ________
- Volume of NaOH used: VB = ________
- Molarity of NaOH (from Part A): MB = ________
- Molarity of Unknown Acid: MA = ________
- Formula: MA × VA = MB × VB
Results
The molarity of NaOH is ________ and the molarity of the unknown acid is ________.