Tea Concentration: Primary Spectroscopy Outreach

Notes for Technical staff and Demonstrators

Session Plan

Timing: 50-60 minutes minimum.

Introduction

Explain the Health and Safety issues of working in a lab to the pupils and their teachers.

Issue pupils with lab coats and glasses Remove any school bags away from walkways etc.

PowerPoint to show white light is separated into different colours

How coloured objects absorb some coloured light and lets other colours through.

Demonstration of the B-Z Reaction to show colour concentration with time.

Using a data projector and laptop and ‘The Chemistry LabSkills’ simulation of colorimeter to look at the measurement of colour intensity. This will not be possible to make widely available for the project so can be left out.

Problem Setting

There are several possibilities for investigation. Split the group into 3 different groups with one group doing one investigation.

Investigation 1: What is the concentration of Marcus’ tea?

Investigation 2: Do different tea bags make the same colour (concentration) of tea?

Investigation 3: Does the temperature of water make a difference to the colour (concentration) of tea?


At the completion of the session the students are brought back together.

The Lead Demonstrator directs the session as the Assistant Demonstrators pack away.

Discussions to be had:

  1. Feedback from each group as to what they have found out for each investigation.
  2. An appreciation of where the errors may be in the experiment.
  3. To list the skills learnt or practiced.


IF time pupils should either get a feedback form OR A CLICKER SESSION TO BE HAD FOR FEEDBACK.

Investigation 1: What is the Concentration of Marcus’ Tea?

Marcus loves his tea to be a certain concentration, how long does he need to keep the tea bag in the boiling water?

Standard Equipment:

For a team of 12 pupils working in pairs this should be:

  • Lab coats and safety glasses (including those for accompanying teachers and other adults)
  • 6x 250mL mugs
  • 6x red alcohol thermometers (-10°C to 110°C)
  • 6x plastic stirring rods
  • 6x stop watches
  • 12x pencils
  • 1x waste bin/waste bucket (household).
  • 6x laminated sheets on how to use the colorimeter.
  • 2x plastic colanders to strain waste

Non Standard Resources

In addition to standard resources pupils will need:

  • Worksheet for experiment 1

Method

Pupils learn to use a Pasteur pipette (Check whether they know already!).
Pupils learn to use the spectrometer.
Pupils set their spectrometer to readings of 100 for pure water.

Pupils have 200mL of boiling water in a 250mL mug and add a teabag. Start a stopwatch. Stir once.
After 60 seconds use pipette to transfer enough tea solution to fill the well in the bubble tray. Stir tea once.
Take a reading every minute for 8 minutes and record it in the table on the sheet.
Take a sample of Marcus’ tea and take a reading and record the result.

Either get pupils to plot the calibration curve OR to inspect the table to ESTIMATE the time for Marcus’ tea to be perfect. Analysis type will depend on (a) time available and (b) ability of the pupils.

Worksheet for experiment 1

 


Investigation 2: Do Different Tea Bags Make the Same Colour (Concentration) of Tea?

When adding boiling water to tea leaves the colour comes out BUT does the same colour come out IN THE SAME TIME for different brands of standard tea?

The task is to compare whether 5 different tea bag brands release the same colour in the same time.

Standard Equipment:

For a team of 12 pupils working in pairs this should be:

  • Lab coats and safety glasses (including those for accompanying teachers and other adults)
  • 6x 250mL mugs
  • 6x red alcohol thermometers (-10°C to 110°C)
  • 6x plastic stirring rods
  • 6x stop watches
  • 12x pencils
  • 1x waste bin/waste bucket (household).
  • 6x laminated sheets on how to use the colorimeter.
  • 2x plastic colanders

Non Standard Resources

In addition to standard resources pupils will need:

  • Sources of several makes of mixed tea leaves (in bags).
  • Worksheet for this Investigation 2.

Method

Pupils learn to use a Pasteur pipette (Check whether they know already!).
Pupils learn to use the spectrometer.
Pupils set their spectrometer to readings of 100 for pure water.

Pupils have 200mL of boiling water in a 250mL mug and add a teabag. Start a stopwatch. Stir once.
After 60 seconds use pipette to transfer enough tea solution to fill the well in the bubble tray. Stir tea once every 30 seconds.
Take a reading after 2 minutes and record it in the table on the sheet.
Carefully empty the tea solution into the waste bucket.
Repeat for another tea brand sample.

Analysis and conclusion drawing will depend on (a) time available and (b) ability of the pupils.

Worksheet for experiment 2

 


Investigation 3: Does the Temperature of Water Make a Difference to the Colour (Concentration) of Tea? 

Standard Equipment:

For a team of 12 pupils working in pairs this should be:

  • Lab coats and safety glasses (including those for accompanying teachers and other adults)
  • 6x 250mL mugs
  • 6x red alcohol thermometers (-10°C to 110°C)
  • 6x plastic stirring rods
  • 6x stop watches
  • 12x pencils
  • 1x waste bin/waste bucket (household).
  • 6x laminated sheets on how to use the colorimeter.
  • 2x plastic colanders

Non Standard Resources

In addition to standard resources pupils will need:

  • Worksheet for experiment 3
  • Extra mugs for cold tap water.

Method

Pupils learn to use a Pasteur pipette (Check whether they know already!).
Pupils learn to use a thermometer (Check whether they know already!).
Pupils learn to use the spectrometer.
Pupils set their spectrometer to readings of 100 for pure water.

The pupils need to make water at 5 different temperature by mixing boiling water with cold tap water in their mugs to a maximum volume of 200 mL
Pupils have access to boiling water and cold water in a 250mL mug and add a teabag. Start a stopwatch. Stir once every 30 seconds.
After 2 minutes (120 seconds) use pipette to transfer enough tea solution to fill the well in the bubble tray. Record the reading and the starting temperature.
Discard the tea solution into the bucket.
Make up the next water sample, take the temperature and repeat.

Either get pupils to inspect the table of results and draw a conclusion.

Analysis will depend on (a) time available and (b) ability of the pupils.

Worksheet for experiment 3

 

Equipment and Chemicals List

  • 4x electric kettles
  • 1x Magnetic stirrer and follower
  • 2x Extension leads
  • 16x 250mL mugs
  • 16x plastic stirring rods
  • 16x heat proof mats
  • 2x litre Schott bottles
  • 8 x Slovenian spectrometers and power adapters
  • 16x plastic pipettes (min)
  • 16x 100mL measuring cylinders for extension exercise. (order new??)
  • 20 x Stopwatches (order new??)
  • X20 red alcohol thermometers (cases for storage/transport?)

Consumables

B-Z reaction

  • Manganese (II) sulfate (pre-weighed in sample tubes)
  • Potassium bromate (V) (pre-weighed in sample tubes)
  • Dilute sulfuric acid (pre-weighed in sample tubes)
  • Malonic acid (pre-weighed in sample tubes)
  • Schott Bottle named ‘Marcus’ Tea’ made fresh for each session (have 3x teabags in 750mL of boiling water for 4-5 minutes (not crucial).
  • Assorted boxes of different bands of teabags
  • Boxes for storage
  • Lab coats (assorted) primary and mixed adults
  • Safety glasses (small) primary and mixed adults


Paperwork (all need project logos)

  • Pupils record sheets
  • x16 Laminated ‘How to use the spectrometer’ sheets with images [Marcus]
  • Laminated sheet showing graph of Marcus’ experiment with ‘Twinning’s All Day Tea’ as exemplar (also showing interpolation line example).

PowerPoint
For introduction


Prepared by: Bristol ChemLabS, University ob Bristol, UK