ingridscience

Lots of people drink filtered water. This activity shows how a filter works.

Take a scoop of grains from the water filter. This is a Brita filter, used in many home water filters. What do the filter grains look like?
Put a full scoop of the filter grains in a tube. Add blue dye to fill the tube halfway. Snap the tube closed.
Half fill a new tube with blue dye only. Close the tube. This is your standard/control. Later you will compare it to the tube containing filter grains.
Start the timer. Shake both tubes hard until the timer is done. Compare the two tubes.
What have the filter grains done to the dye? Where has the dye gone?

How do the filter grains work?
The dye molecules stick to the filter grains: Look at the round beads in your experiment. You may be able to see the blue dye stuck to them.

What happens in a home water filter?
In our home water filters, the filter grains remove chlorine, lead and copper, as well as calcium and magnesium from drinking water.Like the dye in your experiment, the atoms stick to the filter grains:
Calcium and magnesium are natural, harmless, healthy atoms in water, but at high levels they cause blockage in pipes.
Chlorine is added to drinking water to kill harmful bacteria. Some people don't like its taste.
Lead and copper leach from old pipes and are toxic in large amounts.
Although you could see the dye in your experiment, you can't see these atoms in tap water — they are too small and are not colored like the dye.

How much dye can the filter grains remove?
Open your tube containing filter grains and water. Use a dropper to suck the water from above the filter grains. Squirt the water into the trash. Add more dye to the grains. Start the timer and shake the tube again. Do the grains remove these dye molecules as well?

The filter grains in your experiment should have removed more dye molecules from the water. The round beads should have more blue dye stuck to them. In the same way, the filter grains in home water filters can be used over and over to remove unwanted atoms from the drinking water. Eventually the filter grains get full and cannot remove any more atoms. Then you need to replace the filter with a new one.

Experiment!
1. How many filter grains do you need to remove all the dye molecules? Find out by adding different amounts of grains to different tubes. Make sure you add the same amount of dye to each tube. Make sure you shake all the tubes for the same amount of time.
2. How long do you need to shake to remove all the dye? Try shaking different tubes for different times. Make sure the only thing that is different between the tubes is the shaking time — put the same amount of grains and dye in each tube.
3. Try your own experiments. Remember to change only one thing at a time, so you know why you see a difference between tubes.

Introduction:
What is it that makes some foods taste so sour?
Foods are sour when they have a high concentration of loose hydrogen atoms. (Atoms are tiny particles that make up us and everything we see around us. Atoms link together to make molecules.) Do an experiment to predict how sour some foods are without tasting them.

Indicator dye:
Add unknown liquids to wells of the tray.
Add the indicator dye, and look at the colour change. (With red cabbage dye, high concentration of hydrogen atoms turns the dye pink; low concentration of hydrogen atoms leaves it purple, and medium concentration of hydrogen atoms turns it pinky-purple. With commercial pHydrion pH 1-10 indicator dye, high concentration of loose hydrogen atoms turn the dye orange; medium concentration of hydrogen atoms turn the dye yellow; low concentration of hydrogen atoms turn the dye green. )

The liquid with a high concentration of loose hydrogen atoms is the most sour.
The food with a low concentration of loose hydrogen atoms is the least sour.
By looking at the color of the dye, predict which liquid is the least sour and most sour.
Taste the liquids to check. (Sometimes sugar is added to foods to offset the sour taste, so they may not taste as sour as predicted e.g. lemonade).

Baking soda bubbles:
Add a small scoop of baking soda to a well of the tray. Add water and mix together.
Drop a candy into the baking soda solution.
Bubbles will indicate that the candy has a sour coating, as the baking soda and the H atoms of the coating undergo a chemical reaction, making bubbles of carbon dioxide: HCO3 + H -> CO2 + H2O

Why foods taste sour:
In each case the loose hydrogen atoms interact with receptors on your tongue, and depending on their concentration your brain perceives the food as sour or not.

Walk students to the middle of a strip of stores.
Then blindfold one of them, spin them around so that they do not know which direction they are facing in, then ask the other students to lead them into a store that they are familiar with. (Teach the leaders how to allow the blind student lead, rather than pulling them along at a pace that is not comfortable.)
Ask the blindfolded student to state what they smell, hear, touch etc, until they can name the store they are in.
If the student guesses where they are quickly, they can be given the extra challenge of finding a specific location or product in the store.

(Ideas for stores with good smells: pizza place, herb/aromatics shop, coffee shop, plant store, pet store.)

Once the blindfold is off, discuss how our other senses become heightened to compensate for the loss of sight.

Discuss how other animals use their senses of smell and hearing more than humans do.

Discuss how blind people must navigate with their other senses.
Some interesting facts about how blind people sense their surroundings:
Some blind people use echolocation, by clicking their tongues and listening for the echo back to find out where objects are (just like bats or marine animals). Some blind people can so precisely tell where objects are using echolocation that they can use this method for mountain biking or basketball. (Experts in blind echolocation can even listen to a recording of tongue clicks echoing, and state what objects were there when the recording was made!) https://www.youtube.com/watch?v=WHYCs8xtzUI
Brain scans (with functional MRI technology) of blind people using other senses (touch, sound) show that the information from these other senses goes to their visual cortex (just like the visual information in a sighed person). So their brains constructs a visual map of what they "see" using their other senses.

Allow students to try out the devices, and either have them try and figure out how they make heat themselves, or discuss as a group.
Note: probably do not run several hair dryers/space heaters at once or they will trip school electrical fuses.

The space heater, hair dryer, kettle and incandescent light bulb make heat from electricity:
The electrical energy is converted to heat energy by the device, by running a current through a metal coil or plate to heat it up.
In the space heater and hair dryer, the hot metal warms air, then the hot air is blown out with a fan.
The metal coil inside the kettle is heated by electricity, which heats the water above it.
The incandescent light bulb is designed to produce light, and works when electricity passes through a thin wire inside the bulb. The wire heats up an emits light, but also a lot of heat. Incandescent bulbs are not efficient for their purpose as only 5% of the energy emitted is as light - the rest is heat, hence the the conversion to other kinds of light bulbs (fluorescent, now LED).

The candle and hand warmer make heat from chemistry:
The candle gives off heat as the wax burns (a chemical reaction - see candle chemistry activity. A candle is used for light, and also for heat sometimes.
The hand warmer works as sodium acetate crystallizes (turns from a liquid solution to a solid). It is in solution until the metal disc is bent, which initiates the crystallization. You can then see the crystal formation spreading out from the metal disc. Crystallization of this chemical produces heat. (You can reset the hand warmer by heating it up to dissolve the sodium acetate in the water again.) Hence chemical energy is converted to heat energy in these hand warmers.

Other discussion points:
Our bodies make heat from chemical energy.
Rubbing your hands together makes heat from friction.
We heat our homes by burning gas (a chemical reaction that makes heat, similar to the candle), or from electricity (heating up metal inside a device, similar to the space heater and hair dryer).
Geothermal energy is an environmentally sound way of heating buildings - heat is extracted from deep underground and used to directly heat buildings, or used to heat up water that can be used for heating. Thousands of buildings in Richmond, BC are heated in this way.

Logic puzzle to figure out what molecules can make foam
Beforehand, make up dropper bottles of six liquids: water, distilled water, drink mix, soap, skim milk and whole milk (make sure the milks are cold).
Students drip each liquid separately into a tube to fill it half way.
Cap and shake hard.
Look for foam above the liquid i.e. bubbles that remain for more than a couple of seconds. (Make sure the milks are really cold, when they will make foam. The soap will also make foam. The waters and the drink mix should not make foam.)
Figure out which molecules make foam from the liquids that do and don't make foam. This puzzle is most easily done by figuring out which molecules do not make foam, and then deducing which ones must be making foam in the liquids that do foam. Use the attached foam test worksheet to help.

Testing molecules to see which ones make the foam in a recipe or environment
Beforehand, make up dropper bottles of the molecules that are in the recipe or environment:
To find out what makes the foam in meringue make bottles of water, protein (in the egg white), sugar and salt (the cream of tartar).
To find out what makes the foam in milkshake make bottles of water, protein, sugar, salt and fatty acid (all components of milk).
To find out what makes the foam in ocean waves breaking on a beach, make bottles of water, salt, protein (from living things in the ocean) and fatty acids (from living things in the ocean).

In these activities, protein and fatty acids will make foam, but water, salt and sugar will not.

How is the foam made?
Before the tube was shaken, the protein/fatty acid molecules were spread out. During shaking, air bubbles are mixed in. The protein or fatty acid molecules cluster around these air bubbles, holding them in place. The foam you see is hundreds of tiny air bubbles held in place.

More detail: the protein/fatty acid molecules have two different parts - one end of the molecule likes to be in water ("hydrophilic") and the other end does not like to be in water ("hydrophobic"). The hydrophobic parts stick into the air bubbles (so only touch air) and the hydrophilic parts project into the water surrounding the bubbles. The protein/fatty acid molecules surrounding each air bubble stabilizes them so that they remain suspended in the mixture.
Salt/sugar molecules don't cluster around air bubbles, so they don't make foam.

A foam is a kind of mixture called a colloid, with a gas suspended in a liquid. (See the attached mixtures summary for more information on mixtures.)

The attached ocean foam activity booklet is a self-guided activity investigating the molecules that make the foam in the ocean.

Please note that in a class of students it is likely that one of them is at least partially colourblind (1 in 12 males are colourblind). As this is an activity distinguishing colours, these students will not be able to tell some colours apart and perceive some colours differently, although the activity will be no less interesting for them. The common red/green colour blindness means reds and greens (or colours containing reds and greens such as browns) look similar. More information at colourblindawareness.org and colorblindguide.com/post/the-advantage-of-being-colorblind.

One of the fall leaf colours is in leaves all year but is hidden until the fall. Do an experiment to find out which fall colour is hidden in green leaves.

Cut a strip of filter paper about 1cm wide and about as tall as the tube (I make strips 12cm long for my 50ml "Falcon tube" pictured).
Cut a strip of spinach leaf, 1-2mm wide, and tape across the filter paper strip near one end (about 2cm in).
Use a coin to roll over the spinach leaf to transfer the colour from the leaf to the filter paper. (Leave the tape on when you are done, as it might rip the paper if you try and tear it off.)
Fold/roll the end of the filter paper over/around the toothpick, and hang it in the empty tube. Adjust the height so that the bottom of the filter paper hangs about 1cm above the bottom of the tube, and the green pigment is about 3cm from the bottom of the tube. Remove the filter paper and toothpick again.
Add rubbing alcohol to the tube to a height of about 2cm, then hang the filter paper back in the tube, making sure that the green pigment is not submerged, but the end of the filter paper strip is submerged. If it looks like the colour will dip into the liquid, fold/roll the filter paper a little higher. Also make sure that the filter paper is not touching the sides of the tube.

Allow the chromatogram to run. Almost immediately the colours will start to move up the filter paper, but the further up it moves, the more dramatic the separation of the colours will be. I suggest a minimum running time of 10 minutes; 20 minutes or more is ideal, as in the photo.
Note that in a class of students the results will be very variable, depending on how tidy their chromatogram assembly is; however almost all students should see some yellow separating from the green. (Using 70% isopropyl alcohol, the colours move more slowly and are not separated as well with 95% ethanol, so in this case a minimum would be 30 minutes. I have not tried 99% isopropyl alcohol but would guess that it is more like the 95% ethanol.)
To see the colours more clearly while the chromatogram dries, lay on a white paper towel or other white paper.

The leaf pigment molecules are soluble in alcohol and are carried along by it, but they also get caught up on the surface of the filter paper, before moving along again. Each molecule interacts with the filter paper and the alcohol a little differently (as the molecules have different shapes and charges), so they move at slightly different rates up the filter paper. The molecules become separated from each other more and more clearly as the chromatography proceeds.

In spinach leaves, a bright yellow colour separates out from the green.
The yellow is a pigment molecule (called xanthophyll) which moves ahead of the green chlorophyll molecules.
If you try other leaf colours, you will see their colours separate out too. Green leaves only have green and yellow pigment in them. Red leaves may also have yellow pigment in them. Yellow leaves only have yellow pigment in them. Therefore yellow pigment can be masked by the green or red pigments, so is only visible when neither are present.

Relate to fall leaf colours:
The yellow pigment molecules are always in leaves, and help with photosynthesis, but their colour is usually masked by the green chlorophyll. In the fall, the green chlorophyll molecules break down as the leaves die in preparation for winter. As the green molecules disappear, the yellow molecules become visible.
Red and brown pigments are not in leaves before the fall, but made as leaves break apart sugar molecules in preparation for winter. The red molecules appear around the same time that the green molecules disappear.

Lay the cheesecloth over one of the cups.
Secure with an elastic band near the rim of the cup.
Use the other cup to gently push down on the centre of the cheesecloth, while using the other hand to roll the elastic band down a little, to make a well in the cheesecloth.
Add 1 teaspoon lemon juice to the other cup.
Heat the milk in the microwave until very warm (can be done in bulk and while students are preparing cups).
Add 1/4 cup warm milk to the lemon juice in the cup.
Let sit for a minute for the solid "curds" to form.
The watery liquid that separates out from the curds is called "whey".

Protein molecules (specifically casein) in milk mix with the loose hydrogen atoms in the lemon juice (an acid) and a chemical reaction happens, making solid "curds". Heating the milk helps the reaction.
(For older students: the casein molecules in the milk have a negative charge. The loose hydrogen atoms in the acid have a positive charge. Opposite charges attract, so the casein molecules and loose hydrogen atoms group together to make the curds.)

Pour the curds and whey mixture into the cheesecloth on the cup, so that the curds are trapped in the cheesecloth and the whey drains into the cup below.
Pour 1/4 cup of drinking water over the curds to rinse the extra acid off.
Press the curds with the spoon, to drain any last liquid, then scoop out onto a plate.
Add a sprinkle of salt and mix in, before eating on a cracker. It is a great snack food.

Compare taste and ingredients with a commercially-produced cottage cheese.
The cottage cheese ingredients will include some kind of milk, as well as a bacterial culture (e.g. Lactobacillus) which does the same job as the vinegar (see notes below), and likely ingredients that make it more goopy (e.g. guar gum, carrageenen), and possibly some kind of preservative (e.g. potassium sorbate).

Notes on commercial cheesemaking:
Queso blanco (common cheese in Central and South America) is made in the same way as this activity, by adding an acid such as vinegar to warm milk.
Another methods for making a simple cheese use a bacteria (e.g. lactobacillus) instead of adding acid directly. As the bacteria grows it slowly releases an acid (lactic acid), which forms the curds. (Lactobacillus, naturally present in milk, can be used, and/or more lactic acid bacteria can be added.) Cottage cheese is made in this way. (Ricotta cheese is made from whey.)
Rennet is also used to help curd formation by many cheese-makers. It cleaves a piece from casein molecules, which, like the hydrogen ions, cause them to clump together.
Mature cheeses (which take longer to make than simple/quick cheeses) have other bacteria and mould cultures added to give the cheese more flavour and to change the texture. e.g. swiss cheese uses lactobacillus to form the curds, then other bacteria to remove the lactic acid to add other flavours and to make the holes.
https://www.uoguelph.ca/foodscience/book-page/cheese-making-technology-…

Notes on spoiled milk:
When milk is pasteurized most bacteria is killed, including harmful pathogens E.coli and Salmonella. However some spores and some kinds of bacteria survive e.g. lactobacilli. Milk "spoiling" i.e. forming curds when it gets old, is due to the lactobacillus bacteria growing and producing acid. Although lactobacillus is harmless, spoiled milk may also contain harmful bacteria which have grown from spores, so should not be drunk.

See the attached cheese booklet, for an inedible version of this activity run as a stand alone in a science museum (the curds are separated in a centrifuge for speed).

Use the atoms and bonds to build flower pigment molecules.

Use atoms and bonds to build molecules that are smells.

Use molecule models to show how antacid molecules get rid of heartburn.