Methodical
instructions for the 1st year students
Medical faculty
LESSON 6 (6 HOURS)
THEMES:
1. Chemical
kinetics. Influence of different factors on the chemical reaction rate.
2. Catalysis and
catalysts. Influence of inorganic catalysts and enzymes on the chemical
reaction rate.
AIM: To investigate influence
of concentration, temperature and surface area of solid reactants on the reaction
rate; to investigate influence of catalysts and enzymes on a starch hydrolysis.
PROFESSIONAL
ORIENTATION OF STUDENTS:
Chemical kinetics
is the basis for studying rates and mechanisms of biochemical reactions.
Methods of chemical kinetics made it possible to measure rates of absorption
and excretion of medical substances. It is important to know half of substances
to determine shelf life of medicines, accumulation of radionuclides,
pesticides and other harmful substances in the environment. Catalysts made it
possible to accelerate reaction rates, obtain significant industry outputs.
Enzymes are more active than inorganic catalysts. The absolute majority of
biochemical reactions are catalyzed by enzymes. Measurement of enzymes’
activity is widely used for diagnostics of internal diseases.
BASIC LEVEL
Chemical reaction rate
(secondary school course in chemistry)
Chemical
equilibrium. Le Chatelier's principle (secondary school
course in chemistry)
Properties of
catalysts and inhibitors (secondary school course in chemistry)
Concept of enzymes
(secondary school course in biology)
Qualitative tests
on starch (secondary school course in chemistry)
STUDENTS’
SELF-PREPARATION PROGRAM.
Theme
1. Chemical kinetics. Influence of different
factors on the chemical reaction rate
1. Chemical
kinetics. Reaction rate.
2. Rate Law of chemical reaction. The rate constant.
Influence of concentration on the reaction rate.
3. Influence of temperature on the concentration
rate. Van’t Hoff rule.
4. Homogeneous and
heterogeneous reactions. Influence
of surface area of solid reactants on the reaction rate.
5. Order and molecularity of reaction.
6. Activation
energy. Arrhenius equation.
Theme
2. Catalysis and catalysts. Influence of
inorganic catalysts and enzymes on the chemical reaction rate
1. Catalysis. Homogeneous and heterogeneous catalysis. Positive
and negative catalysis. Autocatalysis.
2. The mechanism
action of catalysts.
3. Enzymes as
biological catalysts. Promoters and inhibitors of enzymes.
4. Characteristics
of enzymes: selectivity, dependence enzymes action of temperature and pH
5. Concept of complex
reactions: parallel, consecutive, reversible, chain.
METHODOLOGY OF
PRACTICAL CLASS (900-1200)
Theme
1. Chemical kinetics. Influence of different
factors on chemical reaction rate
Work 1. Determine the effect of the reactant
concentrations on the reaction rate
The experiment is
based on the formation of sulfur, insoluble in water. The equation of the
reaction:
Reaction occurs in
three stages:
Total reaction rate
is determined by the second (slowly) stage.
Materials. 0,1 mol/l Na2S2O3 solution,
0,1 mol/l H2SO4 solution
Protocol. Take six tubes and
add the solutions using the scheme:
|
1 test tube |
2 test tube |
3 test tube |
|
1,0 ml Na2S2O3 and 4 ml water |
2,5 ml Na2S2O3
and 2,5 ml water |
5ml of Na2S2O3
|
|
4 test tube |
5 test tube |
6 test tube |
|
1,0 ml H2SO4
and 4 ml water |
2,5 ml H2SO4
and 2,5 ml water |
5ml of H2SO4
|
Mix the solution
from the first tube with the fourth, the second with the fifth, the third with the sixth.
Note the time from
mixing until the turbidity. Make a conclusion about the effect of the reactant concentration
on the reaction rate.
Work 2. Determine the effect of temperature on the
reaction rate
Materials. 0,1 mol/l Na2S2O3 solution,
0,1 mol/l H2SO4 solution, thermometer, hot water.
Protocol. Add 5 ml of H2SO4
solution to the three test tubes (the first series). Add 5 ml of Na2S2O3
solution to the other three test tubes (the second series). Measure the
temperature of the solution in test tubes with a thermometer (the temperature
of both solutions are the same). Mix the solution from one test tube of the first
series with one test tube of the second series. Note the time (τ) from mixing until the
turbidity. Warm two other test tubes of the first and second series in hot
water to the temperature which is 
Record the results
of the experiment in the table:
|
# test tubes |
temperature, t |
time, τ |
relative rate |
|
1 |
room |
|
|
|
2 |
room+ |
|
|
|
3 |
room + |
|
|
Make a conclusion
about the effect of temperature on the reaction rate. Is Van't
Hoff rule valid for this experiment?
Work 3. Determine the effect of surface area of solid
reactants on the reaction rate.
For the experiments
use a device consisting of two identical tubes connected to U-similar
manometer. Add 2-3 pieces of chalk (calcium carbonate CaCO3) to the test tube,
and the same quantity of powdered chalk to the second tube. Add 25 ml of 10% HCl to two test tubes simultaneously, close the tubes by
cork connected to the manometer. Observe the rate of carbon dioxide allocation,
by the change of liquid level in manometer.
Make a conclusion
about the effect of surface area of solid reactants on the reaction
rate.
Theme
2. Catalysis and catalysts. Influence of
inorganic catalysts and enzymes on the chemical reaction rate
Work 4. Study of starch hydrolysis under the action of
hydrochloric acid
Starch is
hydrolyzed to form glucose in the presence of any strong acid.
Qualitative test
for glucose is Trommer's reagent (a mixture of NaOH and CuSO4). After warming this mixture with
glucose a yellow precipitate of copper (I) hydroxide is formed. The qualitative
test for starch is iodine solution, after mixing of which complex compound of blue
colour is formed.
Materials. 1 % starch
solution, 10 % NaOH solution, 2 % CuSO4
solution, iodine solution, 10 % HCl solution
Protocol.
Add 30 ml of 1%
starch solution and 15 ml of 10% HCl to the flask.
Close the flask with the reverse (air) fridge. Warm the mixture and boil for 10
minutes. Cool the flask. Carry out Trommer’s reaction
and reaction to starch.
a) add to the test tube:
10 drops of hydrolysate (starch solution after boiling)
1-2 drops of iodine
solution
Positive reaction
to starch - a solution of blue color is formed
b) add to the test tube:
8 drops of 10 % NaOH solution;
8 drops of 2 % CuSO4 solution;
5
drops of hydrolysate. Warm the tube.
Positive reaction
to glucose –yellow (orange) precipitate is formed.
Make a conclusion
about hydrolysis of starch under the action of hydrochloric acid
Work 5. Study of starch hydrolysis under the action of
enzymes of saliva and hydrochloric acid at the temperature of
Materials. 1 % starch
solution, 10 % NaOH solution, 2 % CuSO4
solution, iodine solution, 10 % HCl solution,
saliva
Protocol. Add 2 ml of the 1
% starch solution to the 5 test tubes
Add 1 ml of your
saliva and 1 ml of distilled water to the measuring test tube (saliva is
diluted twice). Add 1 ml of this mixture to the first test tube.
For the rest of
saliva add 1 ml of distilled water (saliva is diluted 4 times) to the measuring
test tube. Add 1 ml of this mixture to the second test tube.
For the rest of
saliva add 1 ml of distilled water (saliva is diluted 8 times) to the measuring
test tube. Add 1 ml of this mixture to the third test tube.
Add 1ml of 10 % HCl solution to the fourth test tube.
Add 1ml of
distilled water to the fifth test tube.
Heat all the tubes for
10 min in water bath at the temperature of
Carry out Trommer’s reaction and reaction to the starch in each test
tube.
The results of the work
4 and 5 record in the table:
|
N |
Substrate |
Catalyst |
Tempe-rature |
Reaction to starch |
Trommer’s reaction |
Hydrolysis reaction |
|
1 |
starch |
HCl |
|
|
|
|
|
2 |
starch |
amylase (in saliva, which is diluted twice) |
|
|
|
|
|
3 |
starch |
amylase (in saliva, which is diluted 4 times
more) |
|
|
|
|
|
4 |
starch |
amylase (in saliva, which is diluted 8 times
more) |
|
|
|
|
|
5 |
starch |
HCl |
|
|
|
|
|
6 |
starch |
water |
|
|
|
|
SEMINAR DISCUSSION
OF THE THEORETICAL ISSUES (1230-1400).
TEST EVALUATION AND
SITUATIONAL TASKS.
Multiple choice
tests
1. The rate of
chemical reaction depends on:
A. Volume of
reagent
B. Mass of reagent
C. Concentration of
reagent
D. Surface tension
of reagent
E. Buffer capacity
of reagent
2. Rate Law
equation for the direct reaction: 2NH3(g)
→ N2(g) + 3H2(g) is:
A. υ= k [N2]
[H2]3
B. υ= k [N]2 [H2]
C. υ= k [NH3]2
D. υ= k [O2].
E. υ= k [N2]2.
3. If all the reagent and
products of reaction are in different phases, this reaction is called:
A. Homogeneous
B. Single-phases
C. Different-phases
D. Heterogeneous
E. Similar
4. By what means do catalysts
increase the rate of chemical reaction?
A. Increasing temperature
B. Increasing the concentration
of reactants
C. Increasing activation
energy
D. Lowering activation energy
E. Increasing collision energy
5. What temperature
is optimal for enzymatic catalysis?
A. 37-40
B. 28-32
C. 45-50
D. 50-55
E. 55-60
Examples of solving
tasks
Task
1. How to change the rate of reaction 2A+B2® 2AB, which flows
in a closed vessel, if the system pressure is increased 5 times?
Answer:
|
P2 = 5P1 |
If we increase
the pressure in a closed vessel, the concentration of reactants increases too.
If the pressure increases 5 times, the concentration of reactants will
increase 5 times as well. Dependence of the
reaction rate on the concentration is expressed in the Rate Law. The rate of
reaction before increasing pressure:
The rate of
reaction after increasing pressure:
Find the change in
the rate of reaction:
Answer: The rate
of reaction changes in 125 times. |
|
|
Task 2.The rate constant
for the reaction C +2D ® E is 0,4 l/mol·sec. The concentration of
reagents: C = 3 mol/l, D = 4 mol/l. Calculate the reaction rate of direct
reaction.
Answer:
|
[C] = 3 mol/l [D] = 4 mol/l K = 0,4 l/mol·sec |
Dependence of
reaction rate on concentration is expressed by the Rate Law:
Calculate:
Answer: reaction
rate of the direct reaction is 19,2 mol/sec |
|
|
Task
3. Calculate the overall order of reaction of H2 and I2 interaction.
Answer:
Equation
for the reaction:
Rate
Law for the reaction:
For
this reaction, the rate is the first order with respect to hydrogen and the first
order with respect to iodide. The overall order of reaction is found by summing
the individual orders.
Therefore,
the overall order for the reaction is 2.
Task
4. The reaction rate increases 16 times with increasing the temperature to 20
Answer:
|
∆t = 20 |
Dependence of the
reaction rate on temperature is expressed by the Van’t
Hoff rule:
Calculate:
Answer: the
temperature factor of the reaction is equal to 4
|
|
γ - ? |
Tasks
Task
5. The rate constant for the reaction 2N2O ® 2N2 + O2
is 5 10-4. The concentration of reagent N2O = 6 mol/l.
Calculate the reaction rate of direct reaction.
Task
6. How to change the reaction rate: 2NO(g)
+ O2(g) ®2NO2(g),
if the volume of system decreases 3 times?
Task
7. How to change the reaction rate: 2SO2 + O2® 2SO3,
if oxygen concentration decreases 2 times?
Task
8. Calculate the overall order of the reaction 2NO(g)
+ O2(g) = 2NO2(g).
Task
9. Temperature factor of the reaction rate g = 2,8.
How many times does the reaction rate change, if the temperature is increased
from 200 to
Task
10. How many times does the reaction rate change, if the temperature of
reaction changes from
Task
11. If the temperature increases to
Student should
know:
• The Rate Law of chemical kinetics, the
rate constant;
• Different factors that influence on the
chemical reaction rate;
• Molecularity
and order of the reaction;
• Definition for catalysis and catalysts;
• Mechanism of catalytic action;
• Role of enzymes in the organism;
Students should be
able to:
• Write kinetic equations of the Rate Law
for homogeneous and heterogeneous reactions;
• Calculate changes of reaction rate depending on the
change of concentration and pressure of reactants;
• Make calculations with the Van’t Hoff rule;
• Determine the overall order of the
reaction from its kinetic equation.
Correct answers of
test evaluations and situational tasks:
Multiple choice
tests
Tasks
5. 1,8 10-2 mol/sec;
6. increases 27
times;
7. reduces 2 times;
8. overall order is 3;
9. 7,84 times;
10. 9 times;
11. γ = 3.
References:
1.
http://intranet.tdmu.edu.ua/ Student’s facilities /Lecture presentations
/Department of General Chemistry/ English / medical /1 course/ medical
chemistry/ 07. Chemical kinetics
2.
http://intranet.tdmu.edu.ua/ Student’s facilities /Practical classes materials
/Department of General Chemistry/ medical chemistry/ medical/ 1 course/
English/ 06. Kinetics of biological reaction
3. Atkins, Peter W.; de Paula, Julio. Physical
Chemistry (9th ed.).
4. Atkins, Peter W.; de Paula, Julio. Physical Chemistry
for the Life Sciences (2nd ed.). W.H. Freeman &
Company. – 2011.
5. Petrucci, Ralph H., Harwood, William S.,
Herring, F. G., and Madura Jeffrey D. General Chemistry: Principles & Modern
Applications. 9th Ed. –
6. Ebbing, D.D. General Chemistry. Fifth Edition.
– Houghton Mifflin Co.,
7. Chemistry” 3th ed. J. Mc Murry
and R. Fay; – Prentice Hall,
Methodical
instructions have been worked out by:
Associate Prof. Kyryliv M. V.
Methodical
instructions were discussed and adopted at the Department sitting
27 August 2013. Minute ¹ 1