Download Fun Ideas for using food in Science

Creative Science with Food
1. Making a Naked Egg. (Irreversible changes of state, bases and acids)
What will you need? .
• eggs (enough for one per group or each) • white vinegar • a container big enough
to hold all your eggs and a cover for the container, or plastic cups which can each
hold an egg • a tablespoon
What do you do?
How to dissolve the shell from the eggs:
 Place your eggs in a container so that they are not touching or one in each cup. It
might be handy to set up a few spares in case any break during the process.
 Add enough vinegar to cover the eggs. Notice that bubbles form on the eggs. Ask what
is happening. What can they see ? What do they think might happen? Cover the
container, put it in the fridge for 24 hours.
 Carefully pour out the vinegar and replace with fresh. Put the eggs back in the fridge
for another 24 hours. You can carefully lift the egg out with a spoon while you do this
but be careful the eggshell has been dissolving, so the egg membrane may holding the
egg together. The membrane is not as durable as the shell. If an egg membrane breaks
you will have to throw these away. Discuss what has changed, what do they expect will
happen at the end?
 Scoop the eggs out again and rinse them carefully. When you’re done, you’ll have an
egg without a shell. It looks like an egg, but it’s translucent—and the membrane flexes
when you squeeze it. If you are adventurous you could try some mini bounces to see
how tough the membrane is. What is the membrane left for? What happened to the
shell? What was the shell for?
What is happening?
When you cover the egg in vinegar, the shell dissolves. Vinegar contains acetic acid, this
breaks apart the solid calcium carbonate crystals that make up the eggshell into their calcium
and carbonate parts. The calcium ions float free (calcium ions are atoms that are missing
electrons), while the carbonate goes to make carbon dioxide—the bubbles that you see. This
is the same process as acid rain on a cliff or building or fruit acids on tooth enamel.
Extension.
The reaction of the eggshell and the vinegar is an acid-base reaction. Calcium carbonate, a
base, reacts with the acid in the vinegar to make carbon dioxide. Baking soda is also a base.
So what would happen if you mixed baking soda and vinegar in a plastic bag and tied the
neck?
Notes: As the carbon dioxide is released the bag will swell up like a ballon, if you get it right (
or wrong depending on your point of view) the amount of gas can burst the bag. It can be
quite impressive so I suggest this is best done outside!
2. What else could you do with a Naked Egg? (Osmosis)
What will you need?
.
• at least 2 naked eggs •containers large enough to hold a single egg and some liquid
(a cup is fine) • sugar solution • water • a table spoon
What do you do?
Put one of your naked eggs into a small container and add enough sugar solution to cover the
egg. Put another egg in a small container and add enough water to cover the egg. Put both
eggs in your refrigerator for 24 hours.
After 24 hours,look at your eggs. What can you see? The egg that was in the water is plump
and firm. The egg that was in the sugar solution is flabby and bit shrivelled. Discuss what
might have caused this? What might the membrane be for? Where else might you find a semipermeable membrane?
What is happening?
The naked egg is surrounded by a membrane. This membrane is semi-permeable, it lets some
molecules move through it and blocks other molecules. We call this process osmosis.
Water moves through the membrane easily. Bigger molecules, like sugar molecules cannot
pass through the membrane.
When you put the egg in the sugar solution, the egg membrane separates two solutions with
different concentrations of water. The egg white is about 90% water; sugar solution has less
water. This allows water molecules to move from the side of the membrane where they are
more abundant to the side where they are less abundant. So water moves from inside the egg
to outside the egg, leaving the egg a bit flabby.
Extension..
Can you think of a way to take the flabby egg and make it fatten up again?
Notes:
Put the egg in water for 24 hours. The water will move from the side of the membrane where
water molecules are abundant (outside the egg) to the side where water molecules are less
abundant. After 24 hours, the egg will be plump again. You could experiment with other
solutions salt, food colouring etc too.
3. Making Rainbow Drinks ( Density)
Density is very interesting and not very easy to understand. Rainbow drinks are a good way to
demonstrate density in liquids, plus they look pretty, taste nice and if you use fruit juices they
are even good for you!
What will you need?
 Juices with different density levels. (see below for a simple explanation of
density) The density of a juice is often determined by how much sugar or fruit
is in it, the more sugar or fruit, the more dense the juice is. Fresh juices work
best as canned juices do not work well as they contain too much water.
 A clear plastic cup (the narrower it is, the easier it is to create separate levels)
 Plastic syringes or droppers
What do you do?
1. Start by asking what might happen if you put two of the juices into the same glass.
Demonstrate that it is possible to have one sit above the other. Discuss why this might
be. Pupils could guess which juices will be more dense and form a hypothesis of how
the levels of a Rainbow Drink will turn out, they can use the number of ingredients, the
sugar content, and the water content to explore this.
2. Pour one of your juices into the narrow glass to fill it to 2-3 cm high. Fill a syringe with
another juice and slowly drop it onto the inside of the glass so that it runs down the
inside of the glass. Continue experimenting with other juices to determine which juices
go to the bottom (more dense) and which ones go to the top (least dense.)
3. Once you have the densities determined, start over with a clean glass and use the
dropper for each level to create your final Rainbow Drink, you could always add these to
Cookit too!
What is happening?
The density of liquids demonstrates the amount of “stuff” (atoms, mass) that are present in a
particular volume of the juice. In other words, if you have cup with 100ml of just water, and a
cup with 100 ml of water and lots of sugar dissolved in it. The sugar water will be havier even
though they are the same volume of liquid – the invisible sugar molecules are dispersed in the
water, making it heavier (or more dense.)
4.Testing soft drink v diet soft drinks (Density comparison, floating and sinking,
difference between mass and volume)
What you will need
 Some unopened soft drinks cans (Some diet, some full sugar).
 A clear plastic tub or crate. The deeper the container, the better the effect.
 Scales to weigh the cans
What do you do?
1. Ask "Will this can of soft drink (full sugar) float or sink in the water?"
2. Ask for predictions, place the can of regular soft drink in the water and notice that it
sinks to the bottom.
Teacher’s Note: If the can of full sugar drink floats, there may be an air bubble trapped under
the bottom of the can. Make sure that you test this activity before doing it in class.
3. Pick up a can of diet soft drink and ask the same question. This time the can will float.
Discuss why the result might be different. Encourage the children to work out that the
cans are exactly the same size and shape and contain the same amount of liquid.
4. Why do the children think that diet soft drinks float and full sugar soft drink cans sink?
How could they test this?
What is happening?
Simply put the concept behind sinking or floating is that objects less dense than water float
and those denser than water sink. Hence, empty cans float, rocks sink.
The density of water is 1g/cm3, which means there is one gram of water for every millilitre.
The average density of any object equals its total mass divided by its total volume. So an
object will float if the density is less than 1 g/cm3 and an object will sink if its density is
greater than 1 g/cm3.
If you weighed each can it will be clear that the regular soft drink weighs more than diet soft
drink. This demonstrates the difference between mass and volume. Mass refers to how much
stuff exists within an object. Volume, on the other hand, refers to how much space an object
occupies. The regular soft drink has a greater mass than the diet soft drink even though they
both occupy the same volume.
For fluids, volume is usually measured in litres (L) or millilitres (mL). There are 1000 millilitres
in one litre.
Both cans have the same volume, but one can is heavier than the other – it has a greater
mass. The heavier can is denser than the lighter can.
There are 41 grams of sugar is in every regular Coke can and only 100 mg artificial sweetener
in the Diet Coke can. Only a small amount of artificial sweetener is required to make diet soft
drinks sweet because it is so concentrated. It is the large quantity of sugar that makes regular
soft drinks denser than diet soft drinks.
Where might you see this in the real world?
Perhaps the highest density known is reached in neutron star matter. Neutron stars are the last
stage of a star's life. A neutron star is formed from the collapsed remnant of a massive star or
supernova. A typical neutron star can be twice as heavy at the Sun even though it is 30,000 to
70,000 times smaller.
5. Making Invisible Ink
What do you need?
paper, some milk, a small paintbrush
What do you do?
1. Simply write on the paper with the brush dipped in milk. Many organic substances can
be used in the same way; lemon juice, onion juice.
2. Let the milk dry. When the ink is dry you take a lamp/ hairdryer and if you hold a light
close to the paper the ink will become visible and your message will be revealed.
What is happening?
Milk is an organic product which means it comes from a living thing. When it's heated, it burns at a
slower rate than the paper. Your invisible message shows up brown.
6. How to make Monster Marshmallows
What do you need? .
• marshmallows •a paper plate •a microwave • tongs
What do you do?
1. Put two marshmallows on a paper plate. . Put the plate in the microwave. Set the timer
for 1 minute (60 seconds) on high.
Teacher’s note: DON’T microwave a marshmallow for more than 2 minutes. It will just
turn dark brown and make a sticky mess.
2. Choose a couple of observers to report out loud and ask them to stand and watch
through the window of the microwave. After about 20 seconds, they should see the
marshmallows start to puff up. They’ll grow to about four times their original size! ( This
would make a greatr podcast if anyone s interested in making one)
3. When the microwave turns off, take the plate out and put it where they can be seen.
4. Teacher’s note: The marshmallows will be very hot do not allow pupils to touch them.
5. Wait a few seconds until they have cooled, then pull one marshmallow off with tongs. Is
the marshmallow hollow inside? Is the inside the same colour as the outside? If you
were to you eat it, would it be soft or crunchy?
6. Leave the other marshmallow on the plate and watch it for a minute. When it shrinks
back down, you can pull it with your fingers and make it into whatever shape you want.
It will stay in that shape and get hard and crunchy.
What is happening? .
Marshmallows are mostly sugar and water wrapped around a bunch of air bubbles. When you
cook marshmallows in the microwave, the microwave makes the water molecules vibrate very
quickly—which makes the water heat up. The hot water also warms the sugar, which softens a
little. The hot water also warms the air bubbles.
When you warm air in a closed container, the gas molecules move around faster and push
harder against the walls of the container. As the air in the bubbles warms up, the air molecules
bounce around faster and faster and push harder against the bubble walls. Since the sugar
walls are warm and soft, the bubbles expand, and the marshmallow puffs up. If it puffs up too
much, some air bubbles burst, and the marshmallow deflates like a popped balloon.
When you take the marshmallow out of the microwave and it cools off, the bubbles shrink and
the sugar hardens again. When the microwave marshmallow cools, it’s dry and crunchy. We
think that’s because some of the water in the marshmallow evaporates when the marshmallow
is hot.
If you cook your marshmallow for too long, it turns brown or black inside. That happens when
the sugar gets so hot that it starts to burn.
Useless but interesting fact:
Ancient Egyptians made a puffy white treat out of honey and the dried, carrot-shaped root of
the marsh mallow plant, which grows in fields and swamps. Today we still call these candies
marshmallows, but now they’re made with sugar and gelatine.