Strand 5

• Knows that materials made by chemically combining two or more substances may have properties that differ from the original materials.

• GLEs

Knows the difference between physical and chemical changes

Color Change

• Cornstarch Invisible Ink

• Bleaching Food Coloring

• Acid/Base indicator with pH paper

Concepts

Rxns

Acid/Base Chemistry

Invisible Ink

1. Ink: Mix 2 tbsp cornstarch with 4 tsp water in a pan and heat while stirring until the mixture is smooth. Be careful not to burn it.

2. Message Releaser: Make iodine solution by mixing 1 tsp iodine with 10 tsp water.

3. Write Message: Use the iodine “ink” to write a message on paper and let it dry.

4. Reveal: Brush the iodine “message releaser” over the message with a sponge and the message will appear purple.

What happened?

The iodine and starch in the cornstarch produce a chemical reaction and bind together

The Iodine and starch combined make a chemical that looks purple.

What other chemicals can be used to create an invisible ink?

Any other starch! (try mashed potatoes)

Is it an acid or a base?

Use household items and pH indicator paper to determine what around the house is an acid or a base.

Suggested Items: shampoo, clear dish soap, tap water, milk, ammonia, lemon juice, any liquid can be tested.

What happened?

The indicator paper has a chemical on it that changes color when it reacts with another substance.

The color produced helps us to know if something is an acid or a base because the chemical on the paper reacts differently with acids than with bases, producing a different color.

What other chemicals do you think are acids?

Texture Change

• Class Polymer activity

• Elmer’s Glue Gak (Elmer’s and Borax)

Concepts

Polymer Science

Polymer Crosslinking

PolymersPolymers are made of many chemicals that

are attached to each other, producing a new, very large chemical. DNA is a polymer, so are plastic and wood.

Polymers crosslinked to

form a polymer network

Polymers formation

Individual chemicals

called molecules

Molecules linked to form a

polymer

Class activity: Chemical Mobility

1. Individual Chemicals: Everyone individually move around the classroom.

2. Polymers: Get in groups of four. Hold hands to form a polymer and move around the room.

3. Crosslinked Polymers: Form a polymer network by crosslinking groups of four. Move about the room.

How easy was it to move about the room as you went from a single molecule to a polymer chain and then to a network?

Polymer CrosslinkingGAK

1. Polymer Solution: Mix 1 8 ounce bottle of Elmer’s glue with 8 ounces of warm water in a mixing bowl. Notice the properties and mobility of that mixture.

2. Crosslinking Agent: Add 1 tsp of Borax powder to ½ cup of warm water in a separate cup. Notice the properties and mobility of that mixture.

3. Crosslink: Gradually add the Borax mixture to the glue in the mixing bowl while stirring. You will feel the long polymers in the glue crosslinking. Now stir with your hands! It will get harder to stir. Add Borax until the slime is to your liking. Notice the properties and mobility of the slime.

Phase Change

• Making Orange Soda

• Separating Milk

Concepts

Rxn Products

Reversibility vs. Irreversibility

Orange Soda

1. Start with Liquids: Add ½ cup of orange juice to 1/4 cup of water.

2. Add a Solid: Add 1 tsp of baking soda and observe what happens.

4. Sweeten It: Add ½ tsp of sugar

5. Drink it!

What happened?

We added a solid to a liquid and produced a gas.

The baking soda (or sodium bycarbonate) reacts with the citric acid in the orange juice to form carbon dioxide gas.

All sodas get their fizz from carbon dioxide gas.

What is milk?

1. Start with a Liquid: Fill a baby food jar with whole milk.

2. Add a Liquid: Add two tsp of vinegar, close, and shake.

3. Observe: Let sit two to three minutes and observe.

What happened?

The milk was separated into two parts – a solid and a liquid.

Milk is called a colloid. This means that it is actually a mixture of large particles (the solid) in smaller particles (the liquid). The vinegar changed the pH of the colloid, causing the solids to clump together and separate from the water.

The solid is called a curd and the liquid is called the whey.

Density Change

• Dissolving Styrofoam

Concepts

Phase Change

Color Change

Texture Change

Density Change

Density

• Density is a way to describe the amount of matter in something.

• It is simply the mass divided by the volume of something.

Measuring Density

• Measure the volume of a cube of Styrofoam by measuring with a ruler, the length, width, and height of the cube. Then, multiply these three values.

• Measure the mass of the cube with a balance.

• Divide the mass by the volume and obtain the density.

Changing Density

1. Put the styrofoam cube in a paper cup.

2. Add acetone drop by drop onto the cube until the styrofoam has completely dissolved.

What happened to the volume of the styrofoam?

What would you expect to happen to the density of the Styrofoam if the mass was conserved but the volume was changed?

Further Questions

What happened to the color of the styrofoam?

What happened to the texture of the styrofoam?

What happened to the phase of the styrofoam?

What happened to the density of the styrofoam?