ACKNOWLEDGEMENT:
I would like to express my heartfelt gratitude to my Chemistry
teacher for guiding me throughout this investigatory project.
I am thankful to HI-TECH PUBLIC SCHOOL for providing the
required laboratory facilities.
Lastly, I thank my parents and classmates for their constant
support and encouragement.
INDEX
S. No. Topic
1
Aim
2
Apparatus Required
3
Principle / Theory
4
Procedure
5
Diagram
6
Observation Table
7
Result
8
Precautions
9
Bibliography
(1)AIM:
To study the kinetics of digestion of starch by salivary
amylase and to determine the effect of pH and temperature
on the rate of reaction.
(2) APPARATUS REQUIRED:

Test tubes

Pipettes and droppers

Thermometer

Water baths (ice bath, warm bath, hot bath)

Stopwatch

Starch solution (1%)

Saliva solution (fresh, diluted)

Buffer solutions of pH 4, 7, and 9

Iodine solution (for detecting starch)

Beakers

Measuring cylinder
(3)PRINCIPLE / THEORY:
 Chemical Nature of the Reaction:
Starch is a polysaccharide. Salivary amylase (an enzyme)
catalyzes the hydrolysis:
(C₆H₁₀O₅)ₙ + nH₂O → nC₁₂H₂₂O₁₁
Starch → Maltose
Amylase acts as a biochemical catalyst, altering the rate of
reaction without being consumed.
 Why This Is a Chemistry Experiment?
Because we study:

Reaction kinetics

Effect of temperature on reaction rate

Effect of pH on catalytic activity

Indicator-based qualitative chemical test (iodine test)
 Effect of pH:
Every catalyst has an optimum pH.

At pH 7, amylase shows maximum activity.

Extreme pH values change the structure of the catalyst
→ rate decreases.
 Effect of Temperature (Arrhenius Concept):

At low temperatures: molecules have low kinetic energy
→ slow rate

At higher temperatures: reaction speeds up

Beyond 40–60°C, catalyst (enzyme) is denatured →
reaction stops
This follows the Arrhenius equation:
k = A e⁻ᴱᵃ/ᴿᵀ
Where:
k = rate constant,
Ea = activation energy.
(4)PROCEDURE
A. Preparation of Solutions
1. Prepare 1% starch solution by dissolving 1 g of starch in
100 mL of distilled water and boiling gently.
2. Collect fresh saliva and dilute it with distilled water in
the ratio 1:10 to obtain salivary amylase solution.
3. Prepare buffer solutions of pH 4, 7, and 9.
B. Study of Digestion of Starch by Salivary Amylase
1. Take three clean test tubes and label them A, B, and C.
2. Add 2 mL of starch solution to each test tube.
3. Add 2 mL of salivary amylase solution to each test tube.
4. Place all test tubes in a water bath maintained at 37°C.
5. After fixed intervals of time (1–2 minutes), take a drop
from each test tube and add iodine solution.
6. Note the time taken for the blue-black color to
disappear, indicating complete digestion of starch.
C. Effect of pH on Rate of Reaction
1. Take three test tubes labeled pH 4, pH 7, and pH 9.
2. Add 2 mL starch solution to each test tube.
3. Add 2 mL buffer solution of respective pH to the
corresponding test tube.
4. Add 2 mL salivary amylase solution to each test tube.
5. Place the test tubes in a water bath at 37°C.
6. Test the reaction mixture with iodine at regular intervals.
7. Record the time taken for disappearance of blue-black
color for each pH.
D. Effect of Temperature on Rate of Reaction
1. Take four test tubes and label them 0–10°C, 25°C, 37°C,
and 60°C.
2. Add 2 mL starch solution and 2 mL salivary amylase
solution to each test tube.
3. Place the test tubes in water baths maintained at the
respective temperatures.
4. After fixed intervals, test with iodine solution.
5. Observe and record the rate of disappearance of blueblack color.
E. Observation Recording

The time taken for disappearance of blue-black color is
inversely proportional to the rate of reaction.

Faster disappearance indicates higher catalytic activity
of salivary amylase.
(5)DIAGRAM:
(6)OBSERVATION TABLES:
pH
Time for Blue-Black Color to
Disappear (sec)
Rate of
Reaction
4 Long time / partial fading
Slow
7 Fast disappearance
Fastest
9 Moderate time
Medium
(7)RESULT:

The digestion of starch is fastest at pH 7 and 37°C,
showing highest catalytic activity.

Extremely acidic, basic, or high temperatures reduce the
rate constant (k).

The experiment agrees with Arrhenius theory and
general concepts of chemical kinetics.

Iodine acts as a chemical indicator to detect the
presence of starch.
(8)PRECAUTIONS:

Use fresh saliva for correct catalytic activity.

Maintain precise temperature using water baths.

Add iodine only after removing test tubes from the bath.

Do not overheat saliva; enzyme loses activity.

Use clean and dry apparatus.

Measure time using a stopwatch for accuracy.
(9)BIBLIOGRAPHY:

NCERT Chemistry Class XII

Pradeep’s New Course Chemistry

S. Chand Chemistry Lab Manual

“Chemical Kinetics” – Atkins Physical Chemistry