Activities to do! :P

First Activity ;D - Ice Cream Making 

   What is a summer without ice cream cones, or a slice of apple pie without a melting scoop of vanilla ice cream? Though it looks simple – cream, milk, sugar and eggs – ice cream has some interesting science keeping it together.

Solutions, Emulsions and Colloids

A solution is the result of mixing a solid, liquid or gas into a liquid or gas where the combined substances mix together completely (miscible) and cannot easily be separated – for example, mixing sugar (a solid) into water (a liquid).

A colloid is the result of mixing solids, liquids or gases that do not normally mix together properly (immiscible), with very small particles (1 NM to 1 µam) of one substance becoming evenly spread throughout the other substance. A colloid is stable, so one substance does not settle out of the other. An emulsion is a type of colloid created by mixing two immiscible liquids.

Emulsifiers keep colloids and emulsions stable – for example, in mayonnaise, something called lecithin, which is found in egg yolks, acts as an emulsifier, keeping the oil spread through the watery vinegar. Try shaking together oil and water – the two will settle out from each other. Add a drop or two of washing up liquid (emulsifier) and shake together again – does the water settle below the oil? The detergent acts as an emulsifier, keeping the oil and water mixed together.

Other food colloids include:

• milk – liquid-liquid (milk fat spread through water from the milk)
• mayonnaise – liquid-liquid (oil spread through water from the vinegar)
• butter – liquid-liquid (water from the milk spread through milk fat)
• whipped cream – gas-liquid (air spread throughout milk fat)
• smoke (if you burn something!) – solid-gas (smoke particles spread through air).

Telling the Difference Between a Solution and a Colloid

Put the solution or colloid in a glass jar and shine a torch through it (if the colloid is too thick to allow light through, dilute it with water) – for example, a jar or sugar water, and a jar of milk diluted with water. With a solution (sugar-water), the light will shine through. With a colloid (milk-water), the light will reflect off the tiny particles and will not shine through. This is called the ‘Tyndall effect’.

Ice Cream

Ice cream is a colloid combining an emulsion and a foam, with milk fat, ice crystals and air (a liquid, a solid and a gas) spread throughout another liquid (the water from the milk). In traditional homemade ice cream, the lecithin in egg yolks acts as the emulsifier, keeping the colloid stable. Commercial ice creams may use other emulsifiers, and add stabilisers to stop the air bubbles in the foam disappear.

Once it starts to freeze, ice cream is whipped to add air, creating foam, another colloid (gas-liquid). This also helps the small fat particles join together into bigger ones, which keeps the air bubbles stable. Commercial ice creams may use stabilisers to stop the air bubbles disappearing and keep the ice crystals small.

Making Ice Cream in a Bag

Stir together half a cup of milk and half a cup of cream (or one cup of milk), and quarter of a cup of sugar, pour into a freezer bag, and seal. Put the bag in a bigger bag, and completely surround it with salt (the larger the salt crystals the better) and ice. The salt reduces the temperature even further. It should take about five minutes to freeze. Try shaking the bags while the ice cream freezes to add air – does this make the ice cream softer? Try adding different flavours, like chocolate syrup or jam.

Activity #2 - Getting Critical over Colloids

Getting Critical Over Colloids

What is a colloid? If you have made Oobleck out of corn starch and water, then you know that a colloid is a mixture that acts like a solid and a liquid at the same time! What is the critical factor in making a colloidal material? Will different sources of starch change the recipe?

Objective

The purpose of this project is to find the critical point for colloidal mixtures composed of different types of starches.

Introduction

What do ketchup, Oobleck, and quicksand have in common? They are all made up of tiny, solid particles suspended in water. Chemists call this type of mixture a colloidal suspension, and the amount of solid and water to use is called the critical concentration. The critical concentration for each colloidal material is unique and depends on many different factors.

Colloids have very interesting physical properties. One of the more interesting physical properties of colloidal materials is that sometimes they seem to be solid and other times they seem to be a liquid. Because of this odd behavior, colloids are called non-Newtonian fluids, because they break the rules of ideal fluids described by Isaac Newton in the 1700s.

Colloidal suspensions respond differently to different forces. A fast, hard force will cause the colloid to appear solid, but a slow, even force will cause the colloidal material to flow like a liquid. This can be dangerous if you live in an area with clay soil, because sideways forces during a flood or earthquake can cause the earth to suddenly become very unstable!

As it turns out, colloidal materials are very common. Even though they have such strange physical properties, these properties make them very useful products and materials. Foam, gel, glue, and clay are all examples of colloidal materials. There are many colloidal materials found in food products, like: marshmallows, mayonnaise, pudding, milk, butter, and jelly. Building materials such as cement, stucco, plaster, and paint are colloidal materials. Even our bodies and other living organisms are made of colloidal materials! They are everywhere!

In this experiment, you will learn about a very simple colloidal material: starch suspended in water. You will test starch from different plant sources (corn, potato, rice, tapioca) to see if the colloids share similar physical properties. You will measure the amount of water needed to make a colloid out of each type of starch. Will these colloidal suspensions be the same or different?

Activity 3- Cooking and Mixtures

Activity 4- Making a Gelatin! :D

 Buy some dry gelatin. Dissolve it in warm water and, with subsequent dilutions, determine what is the minimum concentration of dry gelatin necessary to obtain a normal gelatin at room temperature. Do not keep gelatins a long time because they easily become cultures of bacteria. Store them in a refrigerator and, after a day, throw them away. 

 Reversibility of the gelatin. By means of the temperature, make some gelatin pass from the gel to sol states and vice versa.

Activity 5 - Stability of Emulsions!

1 - Stability of the emulsions. Fill two plastic bottles halfway with water, then put 5 cc (about a spoonful) of vegetable oil in each. Only in one of these bottles, put 0.5 cc (about 20 drops) of liquid detergent for dishes. Close the bottles and shake them for a couple of minutes to emulsify the oil, then place them on a table and observe them. The drops of oil will try to reassemble and to surface. By comparing the two emulsions, you will see that the one with detergent will be much more stable (figure 28). In fact, even after a month, the white color of this emulsion indicates that there is a great deal of small oil drops in the liquid, while in the other bottle the liquid is become nearly transparent, this is a sign that near all the oil drops have fused together and surfaced. 2 - Vinegar and vegetable oil. Using a kitchen whisk, emulsify a teaspoon of vinegar with 125 cc of peanut oil or olive oil. The emulsion will result instable.

Figure 28 - The two emulsions of the experiment 1 after 24 hours of rest. In the right bottle, some detergent has produced a more stable emulsion.

3 - Mayonnaise. To the ingredients of the test 2, add an egg yolk and emulsify again. The emulsion will be much more stable. Add some salt and if you want some pepper and you will have obtained a good mayonnaise. If you prefer, you can replace the vinegar with lemon juice. Why is the emulsion stable with the egg yolk? This is due to the presence of lecithin in the egg yolk. Lecithin is a surfactant and the molecules spread on the surface of the oil drops with the hydrophilic head outward. As these heads are electrically charged, the oil drops will repel and their merging is prevented. Lecithin is a phospholipid and it has a structure like that of the phospholipids which form the membranes of cells. Another well known lecithin and which you can find on the market is soy lecithin.

THANKYOU! :D