TITRATION CURVES

EXPERIMENT 4- Investigating Titration Curves For Acid-Base Titration

Date of experiment

Team Role Name of Team Member

Researcher

Technician

Safety Officer

Data Analyst

Introduction

Titration is a process, which consists of the gradual addition of a

standard solution to a measured quantity of a solution of unknown

concentration. In an acid-base titration, the point at which the moles of

hydroxide ion and the moles of hydronium ions are equal in the equivalence

point. The end point will be determined from the plot of pH versus titre. These

titration curves will also be used to determined the pKaor pKb for the weak acid

or base titrated.

In this experiment, the determination of pH is using an instrument called

a pH meter. The pH meter contains two electrodes, one which is sensitive to

the concentration of hydrogen ion. Typically the pH sensitive electrode is a

glass membrane pH electrode, whereas the second electrode may consist of

a silver/silver chloride system, or a calomel electrode. Frequently, a glass

membrane pH electrode is combined in the same physical chamber as a

silver/silver chloride electrode and is referred to as a ‘combination’ pH

electrode. In the solution being measured, the electrical potential between the

two electrodes is a function of the hydrogen ion concentration of the solution.

The pH meter has been designed so that the pH of the solution can be directly

read from the scale provided on the face of the meter.

It is essential always to calibrate a pH meter before use: a solution of

known pH is measured with the electrodes, and the display of the meter is

adjusted to read the correct pH for the known pH solution. A properly

calibrated pH meter provides for much more precise determinations of pH that

does not the indicator method, and is ordinarily used when a very accurate

determination of pH is needed.

Objective

In this experiment, you will investigate two titration curves for the acid-base

reaction outlined in Part A and B. Using the titration curves obtained, you are

going to determine the concentration of acids and also confirm the weak acid

used in Part B is acetic acid. .

Hypothesis

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Reference :…………………………………………………………………………….

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Experimental Procedure

Take great care of the electrode – It is damaged by caustic alkalis. Wash the

electrode system immediately after each titration and allow to stand in a

beaker of deionised water.

You will be provided a calibrated pH meter and standardised sodium

hydroxide solution.

A. Strong acid-strong base titration: Titration of nitric acid and the

standardised 0.1 M sodium hydroxide (NaOH).

1). Pipette 50 mL of nitric acid, HNO3, provided into a 600 mL

beaker.

2). Add 100 mL of deionised water, a magnetic stirring bar and place

the electrodes in the solution (make sure they do not obstruct the

burette and the electrodes are not hit by the stirrer).

3). Record the temperature of the solution.

4). Record the pH at a 0 mL titre and again after adding 5 mL

intervals from a burette for each reading until the titre is 75 mL.

5). Then add 2 mL intervals from a burette for each reading until the

titre is 85 mL,1 mL intervals until the titre is 100 mL and finally 5

mL till the titre 150 mL. Allow time for the meter to come to rest

before each reading.

6). Remove the electrodes from the solution and wash with deionised

water.

7). Plot a graph of pH versus volume of NaOH in the graph paper

provided.

B. Weak acid-strong base titration: Titration of acetic acid with the

standardised 0.1 M sodium hydroxide (NaOH).

1). Repeat the previous procedures 1-3 in section A with 50 mL of

acetic acid, in the beaker and standardised NaOH in the burette.

2). Record the pH at 0 mL titre and again after adding 2 mL intervals

from a burette for each reading until the titre is 30 mL.

3). Then add, 1 mL intervals from a burette for each reading the titre

is 60 mL, and finally 5 mL until the titre 120 mL. Allow time for the

meter to come to rest before each reading.

4). Remove the electrodes from the solution and wash with deionised

water.

5). Plot a graph versus volume of NaOH in the graph paper provided.

Apparatus set-up diagram:

Work Division:

Name Primary responsibility

Safety Precaution:Please refer to MSDS of the following chemicals for the risk/hazard

identification. Specify precautions.

Chemical Risk/Hazard Precaution

HNO3

CH3COOH

NaOH

Data

A. Strong acid- strong base titration – Titration of nitric acid with standardised sodium hydroxide.

VOLUME ( ml) pH VOLUME ( ml) pH

0.00 88.00

5.00 89.00

10.00 90.00

15.00 91.00

20.00 92.00

25.00 93.00

30.00 94.00

35.00 95.00

40.00 96.00

45.00 97.00

50.00 98.00

55.00 99.00

60.00 100.00

65.00 105.00

70.00 110.00

75.00 115.00

77.00 120.00

79.00 125.00

81.00 130.00

83.00 135.00

85.00 140.00

86.00 145.00

87.00 150.00

A. Weak acid-Strong Base Titration: Titration of acetic acid with the standardised sodium hydroxide.

VOLUME ( mL) pH VOLUME ( mL) pH

0.00 44.00

2.00 45.00

4.00 46.00

6.00 47.00

8.00 48.00

10.00 49.00

12.00 50.00

14.00 51.00

16.00 52.00

18.00 53.00

20.00 54.00

22.00 55.00

24.00 56.00

26.00 57.00

28.00 58.00

30.00 59.00

31.00 60.00

32.00 65.00

33.00 70.00

34.00 75.00

35.00 80.00

36.00 85.00

37.00 90.00

38.00 95.00

39.00 100.00

40.00 105.00

41.00 110.00

42.00 115.00

43.00 120.00

Graph:

Graph:

Calculations

1) From your graphs, estimate the equivalence point from the region

where pH changes rapidly with titre (show on the graph)

2) From the equivalent points calculate the actual concentrations (M) of the

a. HNO3 solution

b. HAc solution

3) From titration curve obtained in Part B, find the pKa value of acetic acid.

Compare this value with the pKa of acetic acid in data book.

Discussion

Comment on the shapes of the two titration curves obtained in the

experiments.

Compare the graph plotted with typical titration curves and comment on

points of interest in both titration curves.

Compare and explain the differences of the two titration curves.

Design an experiment:

Devise a plan using similar apparatus and reagent provided in this experiment

to determine the pKa of phosphoric acid in coca-cola beverage.

Apparatus& Reagents Required

pH Meter with pH Electrode 1

50mL Burette 2

Heating Mantel 1

Magnetic Stirrer 1

600mL Beaker 2

100 mL volumetric flask 1

Thermometer 2

Standardised 0.1 M Sodium Hydroxide (500 mL per group)

Nitric Acid (250 mL per group)

Acetic Acid (250 mL per group)

Distilled water