ACID BASE TITRATIONS LABORATORY 4

GEORGIA MILITARY COLLEGE

NATURAL SCIENCE DEPARTMENT

ONLINE CAMPUS

LABORATORY 4 – ACID-BASE TITRATIONS

NAME

STUDENT NUMBER

CLASS

PROFESSOR’S TITLE AND NAME

Introduction

Acid-base titration is a process used to determine the concentration of an acid (or base) whose concentration is unknown by neutralizing it with a base (or acid) of known concentration (Spencer, 2024). The solution whose molarity is known is referred to as the titrant, while that of unknown molarity is the titrand (Spencer, 2024). In the general titration process, the titrand is placed in a flask along with a small quantity of indicator (Spencer, 2024). The titrant is added to a burette and added gradually to the mixture containing the titrand and indicator until the mixture changes color (Spencer, 2024). The volume of the titrant when the color change occurs is recorded and used to calculate the concentration of the titrand using the relationship below:

n acid = n base

But n = MV; and hence

MacidVacid = MbaseVbase

So

Mbase = (MV) acid/Vbase

The above equation (equation 1) gives the formula for obtaining the concentration (M) of a base whose concentration is unknown. Vacid is the volume of the acid (titrant) used in the process of titration, Macid is the concentration of the titrant (acid), and Vbase is the initial volume of the titrand (base). From the titration data, one could generate an acid-base titration curve, which is a plot of the titrand’s pH against the added titrant’s volume at different points of the titration process. The slope of the titration curve will be negative or positive, depending on whether the titrant is an acid (curve will have a positive slope) or a base (curve has a negative slope).

This laboratory sought to realize three core objectives:

i) To enhance understanding of the titration technique

ii) To enhance understanding of neutralizing reactions

iii) To increase ability to develop the titration curve and calculate the concentration of a titrand from titration data.

The laboratory uses phenolphthalein as the indicator. Phenolphthalein changes color during the titration process because the solution’s pH changes as more acid (base) is added to the titrand, making it less alkaline (less acidic) as it approaches the equivalence point. This text hypothesizes that in an alkaline environment, phenolphthalein is pink, and will change to colorless as more acid is added (Spencer, 2024).

Materials and Methods

Preparing the Lab

i) Click on the link labeled ‘Virtual Lab’ on the course home page to activate the lab environment.

ii) Wait for the lab environment to load, then choose ‘File’, and subsequently, ‘Load an Assignment.’

iii) In the category labeled ‘Acids and Bases’, choose the lab 4 assignment titled ‘Prelab exercises: Acid-Base titration’ and choose ‘Problem 3 Solutions.’ You have access to all the materials needed and can proceed to performing the experiment.

Performing the Experiment

iv) Access the ‘Stockroom’ and select ‘Glassware’ tab and then, choose 5mL pipette and empty 250mL Erlenmeyer flask. Click on ‘Other’ and choose 50mL burette.

v) Return to the ‘Stockroom’. In the ‘Solutions’ tab, select Sodium Hydroxide (NaOH) solution (the titrate). Transfer the flask with the 1M NaOH to the workbench.

vi) Select ‘phenolphthalein’ from the ‘Solutions tab’ and transfer it to the workbench.

vii) Select ‘HCL’ from the ‘Solutions tab’ and transfer it to the workbench.

viii) Use pipette to withdraw 5mL NaOH, transfer it into the empty Erlenmeyer flask, and record the solution’s pH and initial volume.

ix) Pour HCL (50mL) into the burette and record the initial volume.

x) Add phenolphthalein (0.2mL) into the titrate (NaOH solution) and record the solution’s color.

xi) Begin titration by placing the burette containing 0.1M HCL into the titrate-containing flask and gradually pour 2mL HCL into the titrate at intervals, recording the solution’s pH and HCL volume each time. Keep adding 2mL HCL until the solution attains a volume of 40mL. Prepare a two-column table to record the solution’s pH and HCL volume as more HCL is added.

xii) Once 40mL of HCL has been added, change the amount of HCL to 1mL, and continue adding 1mL HCL at intervals, each time recording pH and volume. Also, take note of any color changes and record the volume and pH at this point.

xiii) Keep adding HCL after the solution changes color, and recording pH and volume.

xiv) Clear the workbench and begin the data analysis part of the experiment.

Data Analysis

xv) Prepare a titration graph from the data collected during the experiment.

xvi) On the titration curve, show the equivalence point.

xvii) Using equation 1 and the collected data, calculate the concentration of the titrand (NaOH solution).

xviii) Using the collected data, test the hypothesis developed at the start of the lab.

Data and Discussion

Results

Table 1. Titration Data for a Strong Base NaOH with a Strong Acid HCL

HCL Volume

pH of Solution

0ml

2mL

4mL

6mL

8mL

10mL

11mL

12mL

13mL

Figure 1: Titration Curve of a Strong Base NaOH with a Strong Acid HCL

Discussion

The titration curve provides a means to identify the equivalence point in the titration. The equivalence point is the point at which the amount of titrant available is sufficient to neutralize the titrand solution completely (Spencer, 2024). On the titration curve, the equivalence point is indicated by the steepest part of the curve, where there is an abrupt and fast change in the solution’s pH (Spencer, 2024). Given that HCL is a strong acid and NaOH a strong base, the equivalence point occurs at a pH of 7 (Spencer, 2024). At this point, the 2mL of HCL available is sufficient to completely neutralize 5mL NaOH. At this point, the phenolphthalein indicator changes color from pink to colorless. Any further addition of HCL creates an excess of the acid, but does not cause a color change in the solution since phenolphthalein is colorless in acidic environments (Spencer, 224). This finding supports the hypothesis developed at the start of the lab, which stated that phenolphthalein indicator would turn from pink to colorless as HCL is added to the titrand (NaOH) solution. While caution was taken to ensure accurate results, the accuracy of the procedure can be improved further by conducting the experiment multiple times to check for consistency in the collected data.