2. Level 4
Having selected scientific themes of
topical interest, I can critically
analyse the issues, and use relevant
information to develop an informed
argument.
SCN 4-20b
Level 3
Through experimentation, I can
identify indicators of chemical
reactions having occurred.
SCN 3-19a
Through research and discussion, I
have contributed to evaluations of
media items with regard to scientific
content.
SCN 3-20b
Links to Curriculum for Excellence
3. What is Vitamin C?
Ascorbic Acid
Scottish surgeon in the Royal Navy, James Lind, first proved
scurvy could be treated with citrus fruit in experiments he
described in his 1753 book, A Treatise of the Scurvy.
A Common enzyme co-factor.
Deficiency leads to Scurvy
4. Aims of the Practical Workshop
To find out differences between the amounts
of vitamin C in a range of fruits
To carry out a simple titration experiment
To show chemical reactions are taking
place by the colour changes observed
To use reference samples to create a
standard curve
5. How it works
The test involves the reaction of vitamin C in the fruit with
iodine.
Mixing starch with iodine creates a complex with an intense
blue/black colour that is much easier to see than iodine alone.
The iodine reacts with vitamin C, reducing the iodine to
colourless iodide ions.
When all the iodine has reacted with the vitamin C present, there
will be no blue-black coloured complex left, so the mixture is
colourless. This is the end-point of the reaction.
6. The experiment
The procedure is a very simple version of a titration.
Instead of expensive and fragile glassware, we use cheap
Pasteur pipettes.
The ‘volume’ is measured by counting the drops.
Should you wish to calculate a real volume, it is quite
possible. Although there is very slight variation, a 1cm3
pasteur pipette will give 23 – 24 drops per cm3
7. Step 1 – The standard curve
You will use standard solutions of ascorbic acid (vitamin C)
to create a curve that you can use for analysis of the fruit
juices.
Drops of
Vit C/juice
Concentration of Vit C
(mg/100ml)
8.
9. Step 2 – Analysis of the fruit juices
Now you will extract juice from some fruits – and use some
pre-packed fruit juices.
Using exactly the same technique as before, determine the
number of drops of juice it takes to turn the iodine/starch
complex clear.
Use your reference graph to see what concentration of
vitamin C that corresponds to.
10. Aims of the Discussion Activity
To analyse data to establish understanding of
a scientific issue
To be critical of data presented as making a
specific claim
To consider how the work of one scientist
can influence our thinking
11. Discussion Activity
1. Use the sort cards ‘Are Vitamins Needed’ with the class
divided into groups for the activity.
You are given 4 statements about vitamin supplements.
Discuss these in your group and rank them according to
how much you agree with them.
12. Discussion Activity
2. Each group can then be given one type of the colour coded
information sheets to discuss and form opinions on.
The Vitamin sheets are colour coded as each colour contains a
genuine article on vitamins, but they present somewhat
different views on their worth as a supplement.
It is important that students only see and discuss one of the
opinions at this stage.
Editor's Notes
Notes on the sorts of things I might be saying to the group are beneath each relevant slide.
Not sure precisely what. It will probably vary from group to group and depend on the time
Other Possible chemistry links
National 4 - Nature's Chemistry - - plants to products
Higher (revised)
- Consumer Chemistry - 2a Carboxylic acids
- Principles to production 4b Volumetric titration (quantities could be altered slightly to allow use of burette if required)
There are also links to biology and wider aspects of science in society such as nutritional value of foods or the vitamin supplement industry.
Thus, the first Dutch East Indies Fleet sailed in 1595 with 249 men and returned in 1597 with only 88.20 The 1598 fleet took lemon juice, grew horseradish and scurvygrass (a corruption of “scurvy-cress”) on board, and lost only 15 men.
Not adopted by the Royal Navy until the 1790s. ‘Cosseting’ the crew was seen as unmanly.
Lemon juice contains much more Vitamin C than Lime but lemons did not grow in any of the British colonies at the time whereas Limes were plentiful in the Carribbean so lime juice was made part of the daily ration.
As a result, the British sailors in the American War of Independence were called ‘Limeys’ by the rebels – a name that to this day is used for britons.
Colourless compound is Dehydro ascorbic acid – C6 H6 O6
Perhaps emphasise that you don’t need high tech equipment for accurate results.
Eg human eye is much more sensitive to colour than a colorimeter so you can see clear colours (in pale samples) that will not show up on a colorimeter.
In this case – and it ties in with the method – you can increase the path length by looking down the tube and so get a more intense colour than the colorimeter can.
We’ll have copies of the standard curve in case anyone’s experiment doesn’t work.
It’s mentioned in the students’ guide but they will be split into 2 sets, A and B (workstations will be labelled)
For the citrus fruits, there are 5 types, each group in A do one of them and then share. And the same goes for B.
Soft fruit can be squished in a small ziplock (or freezer) bag and the juice used
A sample of vegetable juice will be extracted as well and made available.
There are 7 sets in each classroom.
That should allow for groups of 4 or 5 each time to work together.
Likewise, there are 7 sets per classroom
Depending on how things are going, you could give just the one article each and get feedback, then letting them see the others or just hand out a set to each group and let them see them all.
The thinking is to get pupils to think about the sources of their information. To look at things like the number of studies cited, the number of people involved. What evidence backs up the claims? Are there named people or just ‘scientists’ referred to? Etc.
