# Lab 7: My Second Acid-Base Titration


Learning Outcomes

Upon completion of this lab, the student will be able to:

1. Prepare a solution of primary standard

2. Determine concentration (mol/L) of a solid acid using data obtained from titration

# Introduction

Titration is an analytical quantitative technique used to determine the concentration of an acid or a base. Titrations play an important role in determining amount and purity in many manufacturing processes. These include food processing, textile, wood product manufacturing, petroleum, pharmaceuticals and chemical manufacturing. Titrations play a critical role in the manufacturing of biodiesel, water purification and waste water treatment and even in the production of various products in the dairy industry.

A titration is composed of two solutions: the titrant and the analyte. Typically, the titrant is a solution of known concentration and is slowly added to the analyte. The analyte has a known volume but its concentration is unknown.

## Concentration of the sodium hydroxide solution

Sodium hydroxide is an extremely hygroscopic solid. When solid sodium hydroxide is weighed using an electronic balance it tends to absorb moisture from the atmosphere; this leads to inaccuracies in the mass of the sodium hydroxide and thereby inaccuracies in its molarity calculations.

In order to circumvent the above problem, a sodium hydroxide solution of approximate concentration is prepared first. This solution is titrated with a primary acid standard. The concentration of this acid is known with greater accuracy. The data from this titration is then used to calculate a more accurate value for the concentration of the sodium hydroxide solution. A commonly used primary standard for titration with sodium hydroxide solution is the weak acid potassium hydrogen phthalate or KHP ($$\ce{C8H5O4K}$$).

The reaction between KHP and NaOH is given below:

$\ce{HC8H4O4K + NaOH -> C8H4O4KNa + H2O}$

____ mole(s) of NaOH must be added for every _____ mole(s) of C8H5O4K in solution

The titration of NaOH with KHP involves adding NaOH from the burette to a known volume of KHP. The data from the titration is then used to calculate the molarity of the NaOH.

Fill in the worksheet as you perform today's experiment.

# Experimental Design

Your solution of sodium hydroxide whose concentration is known will be used for this experiment. A solution of KHP that must be prepared by you, the experimenter, and its exact concentration determined by titration with your standardized NaOH.

# Reagents and Supplies

Your standardized solution of sodium hydroxide from last week, solid potassium hydrogen phthalate, and a phenolphthalein solution

(See posted Safety Data Sheets)

# Procedure

## Analyte

1. Calculate the mass of KHP needed to prepare 25.00 mL of 0.100 M KHP.

2. Weigh an amount of KHP as close as possible to the calculated mass in step 1 and record the exact mass of KHP measured.

3. Transfer the solid KHP into a 125-mL Erlenmeyer flask.

4. Add 25 mL of deionized water into the 125-mL Erlenmeyer flask containing the solid KHP.

5. Add one drop of phenolphthalein solution into the Erlenmeyer flask and swirl the flask to mix.

## Titrant

1. Clamp a burette to a burette stand.

2. Condition the burette by filling with water. Allow the water to drain. Water can be discarded in sink. Then fill to mark with your standardized sodium hydroxide solution from last week.

3. Record the initial burette reading. For some burettes, the fill line is marked “zero”

4. Perform a fast titration. Record the volume of NaOH used to reach the endpoint.

5. Repeat steps 2-5 to perform the slow titrations. Record the volume of NaOH used to reach the endpoint.

Lab 7: My Second Acid-Base Titration is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.