Chem 20 AP Standardizing A Solution By Titration A common [PDF]

Chem 20 AP

Standardizing A Solution By Titration

A common laboratory procedure is to determine the concentration of an acid or base solution by titrating it against a solution of known concentration. A titration involves the continuous addition of one solution (the titrant) from a buret into another solution (the sample) in an Erlenmeyer flask until one solution completely neutralizes the other. An indicator solution is used to determine when an acid has exactly neutralized a base, or vice versa. A suitable indicator changes color when equivalent amounts of acid and base are present. The color change is termed the end point of the titration. Indicators change colors at different pH values. Phenolphthalein, for example, changes from colorless to pink at a pH of about 9. In slightly more acidic solutions, it is colorless, whereas in more alkaline (higher pH) solutions it is pink. In this experiment, your solution of NaOH will be standardized by titrating it against a very pure sample of potassium hydrogen phthalate (abbreviated KHP), which has the formula KHC8H4O4 of known concentration. The KHP will be a standard solution that you prepare to have a concentration of approximately 0.125 mol/L. The reaction between NaOH and KHP: KHC8H4O4(aq) + NaOH(aq) → H2O(l) + KNaC8H4O4(aq) You will perform sufficient trials until you have achieved at least 3 concordant equivalence points (total volume of titrant required, volumes within ± 0.2 mL). Once your NaOH has been standardized, a solution of HCl will be standardized by titrating it against the standard NaOH solution.

OBJECTIVES: 1. to accurately prepare a standard solution of KHP 2. to standardize a solution of NaOH by titrating it against the KHP solution 3. to standardize a solution of HCl by titrating it against the NaOH solution

MATERIALS: Equipment clamp stand buret clamp buret

pipet pipet bulb Erlenmeyer flasks

digital scale glass funnel

Chemical Reagents KHC8H4O4(s) to make a 0.125 M standard solution NaOH(aq), unknown concentration HCl(aq), unknown concentration phenolphthalein bromothymol blue PROCEDURE Titration #1 Titrant: NaOH(aq), unknown concentration Sample: 10.0 mL of your KHC8H4O4(aq) standard solution Indicator: phenolphthalein Titration #2 Titrant: NaOH(aq), unknown concentration Sample: 10.0 mL of HCl(aq), unknown concentration Indicator: bromothymol blue

Lab Assignment: You will complete a partial lab report including the following sections: Observations  List out all crucial measurements involved in the preparation of your standard KHP solution  Record your titration data in a suitable table, a separate table for the two different titration reactions Analysis  Show the calculation that determines the concentration of your standard solution of KHP  Show the fully detailed stoichiometry calculation that determines the concentration of the NaOH  Show the fully detailed stoichiometry calculation that determines the concentration of the HCl