st david’s college science department btec applied …

St David’s College

Science Department

BTEC APPLIED SCIENCE TASTER ACTIVITY

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

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.

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)?

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!

Catalase enzyme

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 !!!

Catalase activity

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

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

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).

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)

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?

The Variables – The Independent Variable

Concentration of hydrogen peroxide (%)

•Range: 100%, 80%, 60%, 40%, 20%

The Variables – The Dependent Variable

Time taken for disc to rise to the top of the solution (seconds)

The Variables – The Control Variables

•Volume of solution (cm3)•Area of disc (cm2)•Same volume of potato (cm3)

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

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

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.

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

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.

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?

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.

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

To Ensure Reliability

•The experiment would be repeated for each concentration 3 times (1)

•A mean will then be calculated (1)

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!

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)

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.

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.

Thank you for participating

We hope to see you in September 2020