use. I found out though that if I stirred the potato too much, it didn’t create
as much gas or foam as when I didn’t stir it as much. This is because when I
stir it vigorously, the stirring starts to denature the enzyme and therefore not
as much gas or foam is produced.
I found that when I shook the test tube that the potato and the Hydrogen
Peroxide were in, it sped up the reaction initially but it slowed the reaction
down eventually because the shaking of the test tube denatured the enzyme.
Shaking the test tube also raised the temperature, which could harm results
because if the temperature gets too high it denatures the enzymes and doesn’t
produce as accurate results.
In the experiment I will not shake the test tube, as it would affect the
reliability of the results. Although I will still stir the potato before I
measure out the amount I want, I will only stir it slightly so that the enzyme
is not denatured.
pH
Using pH paper I recorded the pH of the mixture before the experiment and then
after to see if the reaction caused a change in the pH. This could cause a
problem because if the pH did change through the experiment, it could change it
to one in which the enzyme doesn’t work at as the enzyme only works at certain
pH’s. If the pH of the mixture changes, then it could denature the enzymes,
which would affect the reliability of the experiment. I found however, that at
the end of the experiment, the pH of the mixture was the same of that in which
it started off with. As the pH remains constant throughout the experiment there
is no need to control it throughout the experiment.
Liquidised potato
I used 1cm3 of liquidised potato in my preliminary experiment and found that
that was adequate to create a reaction. In two minutes there was enough gas to
collect a good reading and there was enough foam to measure. I have decided to
keep the amount of potato constant as I feel that varying the amount of potato
used would create too much gas and too much foam in two minutes and it would be
difficult to collect accurate results so I will keep the amount of potato that I
use constant throughout my experiment at 1cm3.
Hydrogen Peroxide and Water
I used 5cm3 of Hydrogen Peroxide in my preliminary experiment. I found that the
amount of gas collected and the amount of foam created changed with the
different concentrations of Hydrogen Peroxide, the higher the concentration, the
higher the foam rose and the more the amount of gas collected. I have decided to
use the concentration of Hydrogen Peroxide as my variable in my experiment as it
varies the results but I am still able to collect the results easily. I am going
to use different volumes of Hydrogen Peroxide from 0 to 5 and make sure that the
volume always equals 5cm3 by adding water to substitute for the volume and
dilute the Hydrogen Peroxide. I must make sure that I never use more than 20cm3
of Hydrogen Peroxide in my experiment as it is dangerous and the values I have
chosen do not reach 20cm3 so it should be safe.
I was originally going to find out by how much the foam rises at different
concentrations of Hydrogen Peroxide but I found that that isn’t very accurate
due to foam being made of bubbles which make it very difficult to see by how
much the foam has raised. I have therefore decided to measure how much gas is
given off in the reaction to investigate the concentration of Hydrogen Peroxide.
The amount of gas given off can be measured accurately unlike the foam and
therefore would be a better indicator of how the concentration of Hydrogen
Peroxide affects the enzyme in the potato.
Safety
Hydrogen Peroxide is an irritant and therefore you have to be careful when using
it. Because it is an irritant, gloves should be used to stop it from, if spilt,
spilling on you and damaging the skin. It should be kept away from your skin so
a lab coat should be worn and safely goggles or glasses should be worn at all
times whilst the experiment is in place. In case of contact with Hydrogen
Peroxide in the eyes, the eyes should be rinsed immediately with running water
and medical attention should be sought.
Hydrogen Peroxide is clear and looks like water, which makes it dangerous. Also
no more than 20cm3 should be used at any one time.
Diagram
Table Of Values
Method
· Set up the apparatus shown in the diagram above.
· Using the glass rod, stir the potato so that all the different particles are
evenly spaced out.
· Using the syringe, measure out 1cm3 of the potato and squirt into the test
tube.
· Keeping the test tube upright in a test tube rack so that it doesn’t fall over
and spill the potato, measure out the amount of water that you are using in the
syringe and again squirt into the test tube.
· Measure out the amount of Hydrogen Peroxide needed in the syringe and then
squirt into the test tube, being careful that the rubber bung is placed on top
so that none of the gas can escape.
· Time two minutes on a stopwatch and record the amount of gas that is
collected in the tube.
· Repeat as many times as necessary and change the measurements of the Hydrogen Peroxide and water until all the results are collected.
Prediction
I predict that the higher the concentration of the Hydrogen Peroxide, the higher
the volume of gas that is collected in the tube.
Theory
The higher the concentration of the Hydrogen Peroxide, the higher the number of
particles there are in the same volume. There are therefore more collisions
between reactants therefore the number of successful collisions increases.
Therefore as the volume of the Hydrogen Peroxide increases, the amount of oxygen
collected should also increase.
Table of Results
Analysis
