Chemistry Part 2
Class 2 & 3
Casein (milk) Plastic

You will need
SENIOR CLASSES: YEARS 3-6: One or two bottles of whole milk (depending on the size of the class), one of semi skimmed milk and one of skimmed milk.

JUNIOR CLASSES: YEARS 1&2: only whole milk

SENIORS AND JUNIORS: 500 ML OF MILK PER GROUP (UP TO THREE PUPILS)

White vinegar (one cup per GROUP)

Measuring jugs (ONE PER GROUP)

Metal spoon to stir (ONE PER GROUP)

Kitchen paper

Litmus strips

Cookie cutters

ONLY FOR WORKSHOPS: ONE paper/plastic plate for each student plus one for each group
NO NEED FOR PLATES IN CLUBS BECAUSE YOU WILL USE TRAYS

As well as the usual equipment

GLOVES

Note: at today's class everyone MUST wear goggles and you must wear gloves, when you use white vinegar.

HIGHLY RECOMMENDED:
1) MAKE SOME CASEIN IN ADVANCE. YOU MAY NEED IT FOR YOUR STUDENTS

2) PREP THE MILK BEFORE THE CLASS AND BRING IT TO CLASS IN A THERMOS

A: Non-Newtonian fluids behave as both liquids and solids do, depending on whether (and how much) pressure they face, so they do not follow Newton's law of viscosity and this is why they are called NON-Newtonian.

Newtonian Fluids - don't change (or change v little) under pressure but can change when temperature changes. They are 'incompressible' (can't be squeezed)

Can you give an example of a Newtonian fluid? (A: air, water, alcohol, honey, milk. If you freeze or boil them, they change state and density)

SENIORS ONLY: WHAT WOULD HAPPEN IF AIR OR WATER WERE NON-NEWTONIAN FLUIDS?
(A: THE AIR WOULD TURN THICKER WHEN YOU RUN, SWING A BAT, KICK A BALL. YOU COULD NOT SWIM WITHOUT CHANGING THE VISCOSITY OF THE WATER, BECAUSE YOUR STROKES WOULD PUT PRESSURE ON THE WATER, CHANGING ITS VISCOSITY)

Can you give an example of a Non-Newtonian fluid? (A: ketchup, blood, toothpaste, peanut butter, quick sands. These fluids change viscosity if you shake/spread/squeeze them or move in them)

Step Five: polymers can be natural or synthetic.

Examples of a natural kind of polymers: your DNA, wool, cotton, cellulose (show them a piece of kitchen paper)

Examples of synthetic (man- made) polymers. There are many and we use them every day; plastics, we even wear them acrylic and Nylon (like your tights)

The advantage of these synthetic polymers, like plastics, is that they are:

1) tough and durable, they take hundreds of thousands of years to degrade (melt away) and they are hard to break

2) some of them are easy to bend and to wipe clean, which makes them very practical

3) they are usually non-reactive, which means it's safe to store food in them because they will not react with food and spoil it. Would you buy a plastic bottle of water if you were afraid it could poison you because the plastic has reacted with the water? NO? Neither would I!

Step Seven: pour 500 ml of hot milk (at least 80 degrees) in the measuring jug.
NOTE; IF YOU CAN, PREPARE IT IN ADVANCE AND STORE IT SAFELY IN A THERMOS. Remind them not to dip a finger in it.

FOR SENIOR CLASSES ONLY: The acid we have poured in the milk has lowered the pH of milk from very slightly acidic to very acidic, that's what brings together casein and other proteins in lumps.

Step ten: IF YOU ARE WITH A SENIOR CLASS, NOW COMPARE AND CONTRAST THE CASEIN EXTRACTED FROM WHOLE, SKIMMED AND SEMI SKIMMED MILK.
WHICH ONW YIELDED MORE? WHY?
(A; whole milk contains more fats and casein protein, so it's more nutritious and also yields more casein)

Step eleven: Once you have drained the content of the jug, put the casein in the group tray, wrapping it with paper (it will take a few layers of paper to pat dry well).
Ask the children to go back to their seats and gently tap the casein lump wrapped in kitchen paper to dry it .

Call in the next group, drain their casein and continue until everyone is patting their (still wrapped) casein plastic in their trays.

Tell your students that you will bring string and ribbons next week, so they an take home their pendants with their beads as well as the the cookie cutter decorations, which they can hang in their rooms or even on their Christmas Tree next year.

Cover the trays with the new casein plastic with kitchen roll