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Investigating the Effect of Temperature on the Speed of a Catalysed Reaction

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Investigating the Effect of Temperature on the Speed of a Catalysed Reaction


AIM:-The aim of this investigation is to investigate the rate of a
catalysed reaction, when altering the temperature of the solution and
identify the optimum temperature.

I will see if increasing or decreasing the temperature will make the
rate of reaction faster or slower. In my experiment, I will be using
the enzyme amylase and the substrate starch.

What is the rate of reaction?

In general, rate of reaction is defined as the amount of reactant used
up per second, or the amount of product produced per second. This
means that we can measure the rate of reaction by working out how the
concentration of the reactant changes with time, or how the
concentration of the product changes with time. The formula to work
out the rate of reaction is:-

RATE = Change in amount or concentration of substance

Time taken

There are many factors which can effect the rate of reaction. The four
main factors are temperature, surface area, concentration and pH.

Equation.

The equation for a general rate of reaction between the substrate and
enzyme is:-

Enzyme + Substrate> Enzyme Substrate complex> Enzyme + Product

(Transition state)

The equation that I will be working on is:-

Amylase + Starch> Amylase + Maltose> Amylase + Glucose

What is happening in the equation is that the enzyme amylase is
breaking down the starch to form glucose. It does this by breaking
bonds. Glucose molecules are held together by bonds called glycosidic
bonds. Loads of glucose molecules, joined together by these bonds,
form starch. This type of reaction is known as Hydrolysis because one
of the reactants in the reaction is water. The purpose of the water is
to break and separate the glucose molecules, by joining on to the
glycosidic bond. Diagram 1 shows what is happening through the
reaction.

Starch and Amylase.

The substrate in the reaction is the starch. Starch is a
polysaccharides of glucose. As it is insoluble, it must be broken down
into glucose molecules so that the human intestines can absorb it
through the tissues. Amylase is a digestive enzymes which breaks down
the starch into the monomer, glucose. This reaction takes place in the
mouth cavity and in the small intestines.

What are enzymes?

Many chemical reaction take place inside living cells, and these
reactions are the cells living activities. These chemical reactions
are known as metabolism or metabolic activities, and they either use
up or release energy inside the cell.

These reactions can take place in test tubes but very slowly, unless
pressure and temperature are raised very high. Living cells try to
avoid high pressure and temperatures and so they speed up the reaction
with the use of special chemicals called enzymes.

Enzymes are biological catalyst which speed up the rate of a
biological reaction. Just like normal catalysts, enzymes emerge at the
end of the reaction unchanged and therefore they are not considered as
reactants. Enzymes also don't effect the outcome of the reaction
(product).

Enzymes are made of different amino acids put together to form a
chain, and so they are proteins. There are 23 known amino acids, so
millions of different enzymes can be formed by making different
sequences of amino acids and using different numbers of each type of
amino acid. Enzymes are also very unique and specific. They can only
catalyse one particular type of substrate. An enzyme has three parts
to it's structure:-

1) Primary Structure

The primary structure is the sequence of the amino acids in a chain.
Because there are 23 known amino acids, the number of amino acids in a
chain can vary.

Amino acids are made of different elements and so they could each have
a slightly different charge.

2) Secondary Structure

The secondary structure is the folding of the chain(primary structure)
caused by the hydrogen ions in the amino acids. The hydrogen ions can
attract the opposite charge, building hydrogen bonds between the amino
acids, causing the chain to fold.

3) Tertiary Structure

This structure is known as the globular structure. In this structure,
as well as hydrogen bonds, there are also other bonds called Sulphur
Bridges and Vander Waal forces.

These bonds make the active site and hold it.

It is at the active site, the enzyme interlocks

the substrate molecule and hold it so that the

water molecule can act on it.

But how does the enzyme speed up the reaction? What is happening in
these chemical reactions is that bonds are being broken and built. In
the reaction for my experiment, bonds are going to be broken down. In
order for this reaction to take place, the reactants have to overcome
an energy barrier. This is best achieved by gaining sufficient energy
known as the activation energy. once the reactants have overcome the
energy barrier, they will be in the form of products.

It's a bit like pushing a large rock up a steep hill. Once you have
reached the top of the hill (achieved activation energy) the rock will
roll down the other side very easily.

Although increasing temperature and pressure will increase the rate of
reaction, living cells can not survive these high temperatures and
pressures and so that's where enzymes come in to it. What the amylase
will do in the reaction is that it will lower the activation energy
need for the reaction to take place(make the hill smaller) by lowering
the energy barrier.

During the reaction when the starch molecule is turning into a glucose
molecule, the molecule may be in a very unstable form called the
transition state. These molecules are very unstable because it has a
lot of energy and that is why they are at the top of the energy
barrier.

E1= activation energy for

uncatalysed reaction

E2= activation energy for

catalysed reaction

[IMAGE] = uncatalysed

reaction

---------= catalysed reaction

There are two methods in which enzymes can work and they are the lock
and key theory and the induced fit hypothesis. The lock and key theory
is the idea that the active site in the enzyme is the keyhole and has
a very specific shape. This specific keyhole can only bind with a
specific key which will match the keyhole. The key is the substrate
molecule. Once the key binds with the keyhole, the reaction takes
place.

The induced fit hypothesis suggest that the active site changes it's
shape when the substrate binds to the active site. The active site
does not match the substrate and so can not catalyse the reaction, but
it is suggested that when the substrate tries to bind with the active
site, the enzyme changes the structure of the active site to match the
substrate, because without it changing, the reaction can not occur.
Once the substrate is broken down and the product is released, the
active site will change back to it's original shape.

I think that the starch in the reaction will be catalysed by the
amylase using the lock and key method, because the amylase is a very
specific enzyme and can only catalyse a reaction with the substrate
starch. Therefore it can not be using the induced fit hypothesis,
because if it did, then the active site of the amylase should be able
to change it's shape and catalyse other reactions with a different
substrate.

PREDICTION

I predict that at very low temperatures such as 10 c, the reaction
will take place very slowly. This is because the starch, water and
enzyme molecules have very little kinetic energy and so the frequency
and energy of the collisions will be very low, therefore slowing down
the reaction. At this moment the enzyme is known to be deactivated.

I also predict that as the temperature increases the rate of reaction
will also increase, but only to a certain point, the optimum
temperature. After the optimum temperature, I predict that the
reaction will slow down because the high temperatures will start to
denature the enzyme molecules. This temperature is known as the
optimum temperature.

I predict this because the collision theory states that there must be
two things for a reaction to take place.

1) There must be particles colliding frequently.

2) The collisions that take place must have sufficient energy for the
product to be produced.

So therefore, the increase in temperature will increase the kinetic
energy making collisions more frequent and the particles will be
moving with greater energy.

The collision theory also states that as the temperature increases by
10 c, the rate of reaction will approximately double so we can say
that the increase in temperature is proportional to the increase in
rate of reaction, but only to a certain point, the optimum
temperature. The collision theory states this because the effect of
temperature on the rate of reaction can be expressed as the
coefficient Q10. The formula to work out Q10is:-

Q10= Rate of reaction at (x+10)c

Rate of reaction at x

This means that between 0-40c, the Q10 is 2, meaning that every 10c
raise in temperature, the rate of reaction should approximately
double. Outside this range of 0-40c, in an enzyme catalysed reaction,
the rate of reaction falls and at approximately 60c, it stops
completely.

As I said before, once the rate of reaction reaches the optimum, the
reaction will slow down due to the denaturing of the enzyme molecules.
The reason enzymes denature is because an increase in temperature
causes the kinetic energy to increase, and the bonds holding the
globular structure(tertiary structure) of the enzyme molecule are to
weak to withhold too much pressure and energy. The bonds are so weak
that too much energy can break the bonds, and if these bonds break,
then the enzyme molecule will lose it's three dimensional structure
and distort the active site. Once the active site loses it's shape, it
can no longer bind with the substrate molecule. When an enzyme
molecule is denatured, it can no longer work as a catalyst and so the
more enzymes that denature, the less catalyst molecules in the
solution, therefore slowing down the reaction.

I predict that the optimum temperature should lie in the range between
37-45 c. I know that 37 c is not the optimum temperature because these
type of reactions can take place in a test tube under a lot of heat
and pressure. The only reason why this heat and pressure is not
applied in the body is because the living cells in our bodies can not
survive it. Another reason why the optimum temperature may be higher
than 37 c is because when a person has a fever and the internal
temperature has increased by a few degrees, some enzymes in the body
may denature, but the amylase still works because our food is still
being digested by the use of this enzyme.

I have also predicted what my graph may look like at the end of my
experiments. I can use this graph to compare the actual graph at the
end to see how close my prediction was.

PRELIMINARY WORK

Before I carry out my main experiment, I had to do some preliminary
work to help me decide which starch concentration and what volumes of
starch and amylase would be suitable for the experiment and give
accurate, reliable results. I also had to choose the right technique
in which to carry out my experiments.

Starch concentration

My first preliminary experiment was to find the suitable starch
concentration. The apparatus and substances used for this experiment
are listed below:-

APPARATUS

SUBSTANCES

pipette filler

burette

9 test tubes

pipettes

beaker

stopwatch

test tube rack

stock solution (starch)

water

amylase

iodine

Benedict's solution

I made different starch concentrations by diluting the starch with
water. The highest starch concentration I could use was the stock
solution which was 4%. The volumes of starch and water that were
diluted are shown in a table below. The total amount of solution made
for each sample was 100cm. As this was a lot of solution for each
sample, it would be a waste and so I divided the volumes by 10 so that
I would only be making 10cm of solution. The final volumes I used to
make my solutions are shown in the table.

STARCH CONCENTRATION (%)

VOLUME OF STOCK SOLUTION (cm )

VOLUME OF H2 O

(cm )

4

3.5

3

2.5

2

1.5

1

0.5

0

10

8.75

7.5

6.25

5

3.75

2.5

1.25

0

0

1.25

2.5

3.75

5

6.25

7.5

8.75

10

To make my solutions, I used the burette to measure and fill a test
tube with the starch, and used a pipette filler to measure the water.
To this I added a drop of iodine and the solution went blue/black,
this indicates that there is starch present in the solution. I did
this for all nine samples. Once I had my samples, I took each one and
added 10cm of amylase using a pipette and at the same time, I started
the stop watch. Once the solution went clear, I stopped the watch as
it meant that the starch was completely digested. Just to make sure, I
added a drop of benedicts solution to see whether there was glucose
present in the solution.

The results are shown below:-

STARCH

CONCENTRATION (%)

TIME TAKEN FOR THE STARCH TO DIGEST (min)

0

0.5

1

1.5

2

2.5

3

3.5

4

0

22

>56.5

>48

>40.5

>51

>53.5

>65

>57.5

From my results, I have decided that the 0.5% starch concentration is
the best to use for my main experiment, as it will take the least time
to digest enabling me to obtain my results faster. There will be one
disadvantage that could possibly make my final readings inaccurate,
and that is that the reaction may occur too quickly at high
temperatures and will prevent me from getting an accurate measure of
the time taken. In this case, I would have to use a stronger starch
solution for the higher temperatures, if necessary.

Volumes of starch and amylase

Next, I carried out another experiment to help me decide what volumes
of starch and amylase are suitable for the experiment. The apparatus
and substances used for the experiment are listed below.

APPARATUS

SUBSTANCES

burette

pipette

stopwatch

test tube

test tube rack

0.5% starch

amylase

iodine

Benedict's solution

I took 10cm of 0.5% starch solution from the burette, added the drop
of iodine and using the pipette, I mixed it with different amounts of
amylase each time. I noted down the time taken for the starch to be
completely digested and after each experiment, I washed out the test
tube, so that it is a fair test. The results are shown below.

VOLUME OF 0.5% STARCH SOLUTION (cm )

VOLUME OF AMYLASE (cm )

TIME TAKEN FOR STARCH TO BE

DIGESTED (sec)

10

10

10

1

2

3

360

240

100

From my results, I decided that I would use 10cm of starch and 2cm of
amylase, because it was the most appropriate one. If I used 10cm of
starch with 1cm of amylase, it would take a long time to obtain
results, especially when experimenting with low temperatures. If I
used 10cm of starch with 3cm of amylase, it may be difficult to get
accurate results when experimenting with high temperatures because the
reaction might take place too quickly.

The technique

There are two possible techniques that I could use for the main
experiment. they are the spotting tile technique and the test tube
technique.

SPOTTING TILE TECHNIQUE

APPARATUS

SUBSTANCES

spotting tile

pipette

test tube

test tube rack

burette

pipette filler

stop watch

0.5% starch solution

Amylase

iodine

In this technique, the idea was to put some iodine in each section of
the spotting tile before the experiment actually started. I then took
10cm of the starch solution and to that I added 2cm of amylase. At the
point when they were mixed, I started the stop watch. I took some
sample from the test tube and put it in each section of the spotting
tile (which already had the iodine in it) every 30 seconds. Each time
I took a sample, the iodine indicated and showed me whether the starch
had been digested. At first, the sample should turn blue/black as
there would be starch present. If or when the starch is completely
digested, the solution should remain the same colour as the iodine,
which is brown.

TEST TUBE TECHNIQUE

APPARATUS

SUBSTANCES

test tube

test tube rack

burette

pipette filler

stopwatch

0.5% starch solution

amylase

iodine

Benedict's solution

In this technique, I measured 10cm of starch in to the test tube. To
this I added two drops of iodine. Due to the starch present in the
solution, the solution went blue/black. To this I added the 2cm of
amylase and started the stopwatch. Once the solution went transparent,
it meant that the starch had been completely broken down and so I
stopped the watch.

The best technique

After analysing both techniques, I chose to go along with the test
tube technique as it will give me a more accurate set of results which
are more reliable than the results I would get if I went along with
the spotting tile technique.

The major problem the spotting tile created was the fact that I could
not decide when the sample taken from the test tube remained the same
colour as the iodine when reacted together. The reason for this
problem may be due to the amount of sample taken each time. Some
samples, when taken, had a larger volume than others and so this could
have effected the colour, thus making my results unreliable.

The results I get from this technique are also inaccurate because I
only knew what was happening in test tube every 30 seconds and didn't
know what was happening in between e.g. If I took a sample that
roughly, but not exactly the same colour as the iodine and then after
30 seconds, took another sample, and this time it was identical as the
colour of the iodine, I wouldn't know when in the period of 30
seconds, the reaction was actually over, thus giving me inaccurate
results which are unreliable.

Another problem with this technique was that each time I took a
sample, I didn't know how much starch and amylase I was taking out of
the test tube e.g. I might have taken more starch out than amylase,
changing both of their concentrations in the test tube. This can
effect the rate of reaction as I am introducing a new variable, and
their for it would not be a fair test.

Unlike the spotting tile technique, the test tube technique is much
more quicker. This technique is more accurate and reliable because the
iodine in the solution made it easier to clarify whether the starch
was digested. This technique also pinpointed the exact time for when
the reaction was over, thus giving me a more accurate result.

The test tube technique does have a disadvantage, and that is the fact
that the iodine is being mixed in to the solution at the time of the
reaction.

The purpose of the iodine is to indicate whether there is starch
present in a solution. If there is starch present in the solution, and
iodine is added to it, the solution shoulc go blue/black, to indicate
that there is starch present. The iodine, in this reaction, acts as a
competitive inhibitor. The iodine molecule has an identical three
dimensional structure as the starch molecule, causing it to bind with
the active site of the amylase molecule. If the iodine is joined to
the amylase, it prevents the starch from binding to the amylase
molecule, and so the starch can not be broken down as the iodine has
taken it's place, therefore effecting the rate of reaction by slowing
it down.

This can effect the rate of reaction, but the problem can be resolved.
In my main experiment, I will only use 1 drop of iodine to mix into
the solution. This way, the pattern of the rate of reaction will not
be disturbed, as all the volumes in each experiment will be identical.

From these preliminary experiments, I have decided to use 10cm of 0.5%
starch solution, 2cm of 1% amylase, 1 drop of iodine and use the test
tube method. I'm also going to use burettes and pipette fillers as
measuring instruments as they are more accurate than measuring
cylinders and normal pipettes when measuring the starch and amylase. I
also took readings from the burettes and pipette fillers at eye level
to prevent parallax errors. When measuring a volume, I always took the
reading that was at the meniscus.

THE EXPERIMENT

After doing the preliminary work, I started my main experiment. The
apparatus and substances are listed below.

APPARATUS

SUBSTANCES

2 test tubes

2 glass beakers

1 test tube rack

1 pipette filler

1 pipette

1 burette

2 thermometers

1 stopwatch

1 Bunsen burner

1 tripod

1 gauze

1 heat proof mat

a pair of safety goggles

0.55 starch solution

1% amylase

iodine

benedicts solution

ice

water

I first collected my equipment and set up the experiment. I put some
water to boil in a glass beaker on the Bunsen burner. In the second
beaker, I had ice. These beakers were there to help me keep the
temperature of the solutions constant.

To start my experiment, I measured 10cm of starch which was in the
burette, and poured it into a test tube. To this, I added a drop of
iodine. I then used a pipette filler and measured 2cm of amylase and
poured into the second test tube. I started with the lowest
temperature and worked my way up. I put a thermometer in each test
tube and until the starch and amylase were the same temperature, I
didn't mix them. To make them the same temperature (10 c as it was my
lowest temperature), I kept the test tubes in ice and if the
temperature fell too low, I moved them into the beaker of hot water.
Once they were the same temperature, I poured the amylase into the
starch solution, and at the same time, start the stopwatch.

Once the solution had gone transparent, it meant that there was no
starch present, meaning the reaction was over. I stopped the watch and
noted down the time it took for the starch to be completely digested.
To check whether the solution was transparent, it was best done by
placing white paper behind the test tube, and this way, any colour
that was present in the solution would be visible. Just to make sure
at the end of the experiment, I added a drop of benedicts solution, to
show me if glucose was present. I then washed out the test tube and
repeated the experiment until I got all my results.

To maintain a fair test, I made sure that I used the same volumes of
starch, amylase and iodine. I used only one drop of iodine because
otherwise it would take too long for me to clarify whether all the
starch was digested.

I also had to maintain a constant temperature for each temperature I
was working with, because if the temperature decreased or increased,
it could effect the resulting outcome and the results wouldn't be very
reliable.

To keep the temperature constant, I had to keep a thermometer in the
test tube with the reaction taking place, and keep moving it to and
from the hot and cold beakers. Although this was the only option, this
method didn't work very well because the temperature did rise or fall
by a couple of degrees and so it makes it difficult to believe whether
the results are reliable or not. Due to this, I repeated the
experiment three times for each temperature and I will use this to
find an average enabling me to achieve a more reliable set of results.

MY RESULTS

Table one shows the results I obtained from the experiment. I recorded
the time in minutes correct to one decimal place. I then found the
average time taken for the starch to be digested at each temperature.
The formula to work out the rate of reaction is:-

RATE = 1 / time

TABLE 1

Temperature

( c)

1st attempt

(min)

2nd attempt

(min)

3rd attempt (min)

Average time

(min)

Rate of reaction

(min )

10

44.3

43.4

42.7

43.5

0.02

20

20.1

20.5

19.2

19.9

0.05

30

3.8*

10.2

10.3

10.1

10.2

0.10

40

4.9

5.1

5.0

5.0

0.20

50

1.9

2.2

1.4

1.8

0.56

60

70

0.6

-

3.5*

0.7

-

0.7

-

0.7

-

1.43

-

*Anomalous results, therefore repeated. The new result is shown under
the old.

From looking at my results table, I can see that my results look very
reliable, because after repeating the experiments three times, my
reading for each tempreture are quite similar when comparing.

My results show me that the rate of reaction increases, as I increase
the temperature, which is what I predicted. At 10 c, the rate of
reaction was very low and the reaction took very slowly. On the other
hand, at 60 c, a more higher temperature, the rate of reaction was
very high, infact the reaction took place almost immediantly. At 70 c,
I did not get a reading because the amylase was not able to survive
the high temperature and so it denatured. This meant that it can no
longer work as an enzyme. At the end of each experiment, I did add a
few drops of Benedict's solution into the to indicate whether there
was any glucose present. Up to 40 c, the Benedict's solution indicated
that there was a very high concentration of glucose in the solution.
At 50 c, Benedict's solution indicated that there was a medium
concentration of glucose and at 60 c there was a very low
concentration of glucose present in the solution. This shows that
although the rate of reaction was increasing, the amylase was not
actually breaking down the glucose at high temperatures, such as 60 c.
The reason this might be is because as the temperature increased after
40 c, more and more amylase molecules were becoming denatured.

To see whether my results are accurate, I am going to compare my
results to another group's results. The group used the same volumes of
starch, amylase and iodine and carried out an identical experiment.
Their results are shown below, with the average time and the rate of
reaction.

TABLE 2

Temperature

( c)

1st

attempt

(min)

2nd

attempt

(min)

Average

time

(min)

Rate of reaction

(min )

20

34.6

36.8

35.7

0.03

30

10.9

9.4

10.2

0.10

*40

4.7

1.0

-

-

50

1.7

2.0

1.9

0.53

60

1.8

1.9

1.9

0.53

80

-

-

-

-

*40

4.0

5.4

4.7

0.21

Table two used slightly different temperatures, but they still
obtained similar readings. At 60 c, there is a huge difference between
the rate of reaction in table one and the rate of reaction in table
two. This shows that for this temperature, there has been an error.
This group had the same outcome for 80c as I had for 70 c.

I will now plot both sets of the average times on a graph to compare
them visually.

From the analysis of the graph, there was a big difference with the
time taken for the digestion of starch at low temperatures. At about
30 c onwards, there was a huge ressemblence between the results.They
even shared the same line of best fit perfectly. This shows that
although there was a big difference at low temperatures, the results
were very similar. This also shows that our results look quite
reliable at this early stage.

Now I am going to compare our rates of reaction along with the Q10 to
see if they have a relationship between them. The table below shows
the Q10 for my rates and the Q10 for the other group's rate. The
formula to work out Q10 is:-

Q10= Rate of reaction at (x+10)c

rate of reaction x

Temperature

( c)

Q10 for my rates

Q10 for other group's

rates

10

2.5

-

20

2

3.4

30

2

2.1

40

2.8

2.5

50

2.6

1

60

-

-

70

-

-

80

-

-

The Q10 theory stated that the relationship between the rate of
reaction and temperature was that they were prortional, but thats only
for the temperatures between the range of 0-40 c. It stated that for
every 10 c rise in temperature, the rate of reaction will
approximatley double. It will double because if the Q10 is worked out
for any temperature within that range, the Q10 will always be 2.

After working out the Q10 for both sets of results, it looks like my
resuls look more accurate and reliable than the other results because
my results have clear evidence that the temperature was almost
proportional to the rate of reaction, as the Q10 was frequently 2.
After 40 c, the Q10 for my rates were no longer 2 and so the
temperature and the rate of reaction was no longer proportional. I had
predicted that after 40 c, the reaction would slow down, but my rate
of reaction still did increase all the way to 60 c, and then stopped
compltely. However, the other groupes results also showed the rate of
reaction increasing untill 60 c, but their Q10shows that it was not
increasing proportionally and that after 40c, the rate of reaction
increased slowly. From this I conclude that the Q10 theory is the
truth, and my results partially show this, but not completely. This
could because my experiments were not 100% reliable and accurate.

The graph of my rate of reaction against temperature has a similar
pattern to the Q10 graph. This shows that my results are fairly
reliable. The other group's graph starts of being almost identical to
my graph. This also shows that my results are fairly reliable. Both
the graphs have a similar pattern to the Q10graph at the begining. The
only difference is the optimum temperature. The Q10 graph shows it's
optimum temperature to be about 40 c, whereas the other two graphs
show their temperature to be between 50-70 c. What looks odd though is
that at 60 c, my graph shows the rate of reaction to be very high
compared to the other group's rate of reaction. Between 50-60 c, the
rate of reaction for the other group hardly increased, whereas my rate
of reaction at 60c went up rapidly from 50 c. This shows that at this
point, the results are not reliable and that there must have been an
error in one of the experiments, or there was a lack of accuracy in
the experiments.

When I look back on my prediction, I had predicted that at low
temperatures, the reaction would take place slowly as there wouldn't
be suffecient kinetic energy. My graph does agree with this
prediction. The lowest rates of reaction did take place at the low
temperatures. The low temperatures didn't seem to be giving particles
enough kinetic energy and force for frequent collisions to take place.
This is what made the reaction take place very slowly.

I had also predicted that when the temperature is increased, the rate
of reaction will also increase, but only to the optimum temperature. A
fter the optimum temperature, I predicted that the rate of reaction
will start to decrease. However, I predicted that the optimum
temperature would lie between 37 -45 c. From looking at the graph, the
rate of reaction was still increasing after 45 c. The high
temperatures were giving particles a lot of kinetic energy and force,
and so collisions were more frequent, enabling the reaction to take
place faster.

My graph shows me that the opyimum temperature lies between 60-70 c
because at 60 c, the reaction took place almost immediatly and at 70
c, the amylase started to denature due to the high temperature. The
amylase could not withold the huge amount of energy given at +70 c,
and so the three dimensional globular structure of the enzyme was
destroyed, leading to the distortion of the active site. The amylase
had precipitated out of the solution, forming a cloudy foam. The
blue/black solution of the iodine and starch went clear at 70 c. This
may be because the high temperatures may have inturrupted the reaction
between the starch and iodine.

Another prediction I had made was that, due to the coeffecient Q10,
every raise in 10 c on the temperature would double the rate of
reaction, but only to the optimum temperature. After working out the
Q10 for my results, I would say that the rate of reaction did
approximately double as I raised the temperature by 10 c each time.
The rate of reaction may not have exactly doubled due to the lack of
accuracy in the experiments.

I had predicted that the optimum temperature must be higher than the
internal body temperature and my graph proved that this was true.
However, I had also predicted that the optimum temperature would be
lower than 45 c. This didn't agree with my results. The reaction was
still taking place at 60 c and it took place much more faster than it
took place at 40 c and 50 c.

EVALUATION

After doing this investigation, I think my results are not 100%
reliable because there were many factors in the experiments which may
not have been completely accurate.

One factor was the iodine. Although the iodine was an inhibitor in the
reaction, the pattern of the rate of reaction should not be effected
because I used identical volumes of starch, amylase and iodine each
time. However, the dropping pipette for the iodine may have had too
much iodine at one time than it did at another. If this is true then
it could have effected the pattern, making my results slightly
unreliable. This could be changed and the volume of the iodine could
be made more accurate by using a pipette that measures to two decimal
places or by using a burette, instead of a dropping pipette.

Another factor was the starch solution. It may be possible that the
starch suspension in the burette may not have been a true solution,
because the starch is not fully dissolved in to the water and
therefore the starch would settle at the bottom of the burette, whilst
all the water settled at the top as it is more denser. If this is
true, then some of the starch solution at the beginning of the
experiment would have a higher concentration than the solution at the
end. This would effect the rate of reaction as I would be introducing
a new variable, thus making my results unreliable as it wouldn't be a
fair test. This could be changed by stirring the solution
occasionally, mixing the starch and water into an equal distribution
in the solution.

It was also confusing whether the reaction as over or not. At some
points, it was difficult to see whether the solution was transparent
or still pale blue. This may have made my results inaccurate. To solve
this problem, I could use a device called a colourimiter to help
clarify whether the solution is transparent.

The temperature of the solutions during the experiments were not
always constant, and always increased or decreased by a few degrees.
This also made my results inaccurate which didn't make them very
reliable. To improve this, I could use a number of water baths, each
set up to a certain different temperature and to place the test tubes
in. This way the solution would stay constant through the process of
the reaction. In my experiments, I had used an alcohol thermometer.
These thermometers are not very accurate and so in my experiments,
when I took a reading from the thermometer, it may not have been a
true temperature, meaning it wasn't accurate and therefore it effected
the results. This could be changed by using a mercury thermometer
instead as they are the most accurate type of thermometers.

After obtaining my results, I realised that I had two set of results
that were completely anomalous. I am not sure what cause them to be
strange, but it may have been the temperature keeping. It was
difficult to keep a constant temperature and I may have mistaken the
temperature on the thermometer for another temperature.

For the second anomalous result, I realised I had put two drops of
iodine instead of one, but I carried on with the experiment to see if
it effected the rate of reaction, as iodine is an inhibitor. As the
result was anomalous, the iodine had effected the outcome. I did
repeat the anomalous results and obtained better readings. I didn't
use the anomalous results to find an average as they were untrue,
therefore unreliable.

From looking at my results plotted on the graph, I could investigate
further by carrying out experiments in between the range of
temperatures, where the optimum temperature lies, to pinpoint exactly
where the optimum temperature is. To see whether my conclusions are
correct, I could set up another different experiment, for the same
variable to see whether I get a similar pattern. I could do this in
many ways. I could use the same volumes of starch, amylase and iodine,
but apply the changes I made earlier. I could use a more accurate
measuring pipette for the iodine, use set temperature water baths, use
a starch suspension which is true and making it true where all the
starch and amylase is equally distributed in the solution. I could
also use the colourimiter to pinpoint exactly when the reaction is
over.

From the analysis of my results and method, I can't say that my
results are 100% accurate and reliable, but I could investigate
further in many ways by creating different experiments, which will
give me a more accurate reliable set of results and a conclusion which
is 100% reliable.

How to Cite this Page

MLA Citation:
"Investigating the Effect of Temperature on the Speed of a Catalysed Reaction." 123HelpMe.com. 19 Apr 2014
    <http://www.123HelpMe.com/view.asp?id=122413>.




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