st david’s college science department btec applied …
TRANSCRIPT
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St David’s College
Science Department
BTEC APPLIED SCIENCE TASTER ACTIVITY
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Introduction - Hydrogen PeroxideHydrogen Peroxide is a toxic chemical produced in many industrial processes as well as in nature by all cells.
Hydrogen Peroxide decomposes naturally in the presence of ultra violet and visible light VERY SLOWLY. It can be used as contact lenses solution and stored safely for months, even years.
Hydrogen Peroxide can be decomposed both in industry and our cells, catalysts are used.
What are the benefits of catalysts? Revise catalysts: https://www.bbc.co.uk/bitesize/guides/zygxdxs/revision/5
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Decomposition of Hydrogen Peroxide
Hydrogen Peroxide decomposes via the following equation
H2O2 à H2O + O2
Can you balance the equation?
2H2O2 à 2H2O + O2
There are many catalysts that can be used to catalyse this reaction.
Firstly, we will watch a clip that uses Manganese Dioxide as a catalyst to decompose hydrogen peroxide.
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Decomposition of Hydrogen Peroxide
• What was the effect of using the Manganese Dioxide?• Why do you think this this chemical is useful in industry? Would it be useful
in our bodies (cells)?
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Catalase enzyme (in the liver)
Catalase is an enzyme that breaks down harmful hydrogen peroxide into water and oxygen inside liver cells.
Just one molecule of catalase can break down 600,000 molecules of hydrogen peroxide EVERY SECOND!QUIZ ON ENZYMES!
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Catalase enzyme
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HOOH H H
O + O O2 2
E Ea = 75 kJ mol-1 at 293 KEa = 58 kJ mol-1 with MnO2
Should react 1000 times faster with
MnO2 !!!
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Catalase activity
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Catalase activity• Catalase activity can be affected by many factors-Temperature-pH-Enzyme concentration-Hydrogen peroxide concentration
You are going to virtually investigate HYDROGEN PEROXIDE CONCENTRATION
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Apparatus and Reagents• Freshly cut potato cylinders• Pestle and mortar• Specimen tubes/test tubes x 5• Stock solution of hydrogen peroxide• Filter paper discs• Forceps• Stopwatch• Syringe x 2 (1 for water and 1 for H2O2)• Small beaker x 2 (for distilled water)• Distilled water• Paper towel
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Prediction
• What do you think will happen in this experiment? Write a prediction.
• E.g. As the concentration of Hydrogen Peroxide solution increasing I expect the time it takes the disc to sink and float up again will….
• Then add an explanation (a reason why).
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The Prediction
• As hydrogen peroxide concentration increases the time taken for the disc to rise to the top will decrease (1)• As substrate concentration increases there will be more
successful collisions and more enzyme substrate complexes made (with catalase and hydrogen peroxide) (1)• A greater volume of oxygen will be produced in a shorter
period of time causing the disc to rise more quickly (1)
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Variables
• What would be your independent and dependent variable? Remember that the independent variable is the one YOU decide to change whilst the dependent variable changes as a result of it.
• Can you think of any variables to control to ensure nothing else affects the results?
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The Variables – The Independent Variable
Concentration of hydrogen peroxide (%)
•Range: 100%, 80%, 60%, 40%, 20%
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The Variables – The Dependent Variable
Time taken for disc to rise to the top of the solution (seconds)
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The Variables – The Control Variables
•Volume of solution (cm3)•Area of disc (cm2)•Same volume of potato (cm3)
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The Independent Variable- the concentration What volumes will you use?
Concentration/ %
Volume of H2O2/ cm3
Volume of water/ cm3
20 2.0 8.040 4.0 ?6080
100
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The Independent Variable- the concentration What volumes will you use?
Concentration/ %
Volume of H2O2/ cm3
Volume of water/ cm3
20 2.0 8.040 4.0 6.060 6.0 4.080 8.0 2.0
100 10.0 0.0
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The Results Table – why it is arranged like this?
Concentration of hydrogen peroxide/%
Time taken for disc to sink and rise to the surface (s)
1 2 3 Mean
20
40
60
80
100
Answer: The independent variable always goes on the left.
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Exemplar results
Concentration of hydrogen peroxide/%
Time taken for disc to rise to the surface (s)
1 2 3 Mean
20 201 198 196
40 177 172 187
60 103 114 113
80 54 58 42
100 47 35 39
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Make a graph
• First work out your mean• You can draw a graph in excel or hand drawn on paper (please print the
graph paper provided).
• Your independent variable goes on the x (horizontal) axis and dependent on the y.• Use a small ‘x’ to mark your plots and join them with a ruler.
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How to make the graph in excel • Add the range of concentration to the left hand column (see below) and the
mean on the right (note this mean data is not calculated)
• Highlight both datum then choose XY Scatter with lines (see below)
• Can you label the X and Y axis with the correct units?
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Control experiment
• This is an experiment to check that everything is working as it should. i.e the enzymes are causing the disc to float in Hydrogen Peroxide.
• What experiment would you do to check this?
Work your way through the rest of your worksheet and use the rest of this PowerPoint to check your answers.
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Control Experiments
•Add the disc to a test tube with water only (1)•OR Add the disc with no potato homogenate to hydrogen peroxide (1)•OR boil the enzyme for 5 minutes to denature it•AND All other conditions must remain the same, 2 listed; volume of hydrogen peroxide solution, area of disc, same volume of potato
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To Ensure Reliability
•The experiment would be repeated for each concentration 3 times (1)
•A mean will then be calculated (1)
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What does the trend show?
•FULL description of trend (1)
•Using data (1)• E.g. As the concentration of H2O2 increased the time it
took to float decreased. At 20% it took 198s whilst at 100% it only took 40!
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EXTENSION: Improvements – watch the experimental clip again to help
•Keep all other factors the same e.g. volume of hydrogen peroxide solution, concentration of hydrogen peroxide solution, area of disc, etc. (1)•Repeat the experiment with at least 5 different temperatures. (1)
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Sources of Inaccuracy
• Each disc contained a different concentration of catalase –use a fixed volume of catalase in each test tube.• Some discs did not sink as quickly – time from when the disc
reaches the bottom of the test tube.• The temperature was not monitored so it may have varied
through the experiment – complete the practical in a thermostatically controlled water bath.
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What can you expect to study in BTEC Applied Science and how will you be assessed?
You will study chemistry, biology and physics. There is an externally assessed exam which is split into 3 sections (one for each science) and each section is worth the same number of marks.
As well as these exams, you will also complete assignments that are marked by your teacher and timed tasks that will be sent to an examiner to mark.
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Thank you for participating
We hope to see you in September 2020