2.4 Chemical Reactions > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.. Chapter 2 Matter and Change 2.1 Properties of. - ppt download

2.4 Chemical Reactions > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.. Chapter 2 Matter and Change 2.1 Properties of. - ppt download: 2.4 Chemical Reactions 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.. Chemical Changes What always happens during a chemical change?

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BIOLOGY: Test for Starch

 Experiment 1. The test for starch

(a) Label four test-tubes 1-4.

                                                         10% glucose solution into tube 1

                                                         1% starch solution into tube 2

(b) Put about 20 mm (depth) of

                                                         1% albumen solution into tube 3

                                                          water into tube 4

(c) To each tube, using a dropping pipette, add three drops of iodine solution.  Shake the tube (sideways, not up and down) to mix the contents. Look for any colour changes apart from the yellow colour of iodine itself. Copy the table below and record the results in your notebook.

Substance	Colour change after adding iodine
10% glucose solution
1% starch solution
1% albumen solution
water

Experiment 1. Discussion

I The substances selected for testing are examples of three of the principle chemical substances in cells, sugar (glucose), starch, protein (albumen). With which of these substances did iodine react to give a colour change ?

2 Does your result indicate that there is, for example, no sugar and no protein that will

give a colour change with iodine ?

3 What experiments would you have to carry out in order to give a confident answer to

question 2 ?

4 Does the result indicate that starch will always react with iodine solution to give a

colour change?

5 What was the point of the water in tube 4 ?

Experiment 1. Discussion - answers

I Only the starch should give a blue colour. The glucose and albumen solutions may take up the colour of the iodine.

2 The point is being made that the results from a single sample do not justify a sweeping generalization.

3 One would have to test samples of all sugars, all proteins and all fats.

4 The results permit confident prediction only about starch as a 1% aqueous solution.

5 Students often say that the unreactive samples have 'turned yellow'. This control shows that the yellow colour is simply the diluted iodine.

TEACHERS NOTES

Experiment 1. The test for starch - preparation

Outline The experiment establishes that iodine gives a blue colour with starch, but not with glucose or albumen.

Prior knowledge Use of test-tubes and dropping pipettes.

Advance preparation and materials *

     10% glucose solution

                                         

     1% starch solution                 10 cm³ per group

                                  

     1% albumen solution

     iodine solution                        5 cm³ per group

Apparatus-per group

test-tube rack  and 4 test-tubes                        

4 labels or spirit marker                                   

dropping pipette (for iodine)

                  

* Instruction for preparing reagents are given on p. 01

Reflecting Light Experiment

Shiny Spoons

 Materials you will need:

• Smiley Face
• Shiny Spoon

Steps:

1.  Look at your reflection on the inside of the spoon.

The surface on the inside of a spoon bends in like a cave - it is concave.

Dentist use concave mirrors to examine your teeth.  These mirrors make your teeth look bigger so the dentist can examine them more easily.  Likewise, shaving mirrors are concave because they make the face look bigger.

2.  Now turn your spoon out and look at your reflection on the outside of the spoon.

The surface on the outside of a spoon bends out - it is convex.

The next time you are at a funfair take a look at yourself in the crazy mirrors.  They bend in all sorts of ways so that you look bigger, smaller, fatter, thinner and even wavy.

Rapid Color Changing Chemistry

Rapid Color Changing Chemistry!

Sometimes it’s hard to tell SCIENCE from MAGIC - and this little demonstration is a great example of that. In this experiment you will watch an almost clear liquid suddenly turn dark blue in a flash. It takes a bit of preparation, and probably a trip to the pharmacy for materials, but we think it’s worth it.

IMPORTANT SAFETY INFORMATION: This experiment should only be done with the help of an adult. Iodine will stain just about anything it touches and it can be hazardous. Hydrogen peroxide can cause eye and skin irritation - safety goggles are needed throughout the experiment. Be sure you're helpful adult reads the caution labels on each container.

• 3 clear plastic cups 4 ounces or larger
• A 1000 mg Vitamin C tablet from the pharmacy (you can also use two 500mg)
• Tincture of iodine (2%) also from the pharmacy
• Hydrogen peroxide (3%) yep, also from the pharmacy
• Liquid laundry starch (see below for alternatives)
• Safety goggles
• Measuring spoons
• Measuring cup
• An adult helper

1. Put on those safety goggles and mash the 1000 mg Vitamin C tablet by placing it into a plastic bag and crushing it with a rolling pin or the back of a large spoon. Get it into as much of a fine powder as possible. Then put all the powder in the first cup and add 2 ounces (60 ml) of warm water. Stir for at least 30 seconds. (The water may be a little cloudy) Let’s call this “LIQUID A”
   
2. Now put 1 teaspoon (5 ml) of your LIQUID A into a new cup and add to it: 2 oz (60 ml) of warm water and 1 teaspoon (5 ml) of the iodine. Notice the brown iodine turned clear! Let’s call this “LIQUID B.” By the way, you’re done with LIQUID A - you can put it aside.
   
3. In the last cup, mix 2 oz of warm water, 1 Tablespoon (15 ml) of the hydrogen peroxide and 1/2 teaspoon (2.5 ml) of the liquid starch. This is, you guessed it, “LIQUID C”
   
4. Okay, that was a lot of preparation, on to the fun part. Gather the friends and family and pour all of LIQUID B into LIQUID C. Then pour them back and fourth between the 2 cups a few times. Place the cup down and observe….be patient....somewhere between a few seconds and a few minutes, the liquid will suddenly turn dark blue!

This is an example of the chemical reaction know as the IODINECLOCK REACTION. It is called a clock reaction because you can change the amount if time it takes for the liquids to turn blue. (see experiments below) The chemistry of the demonstration gets a bit complicated, but basically it is a battle of chemistry between the starch which is trying to turn the iodine blue, and the Vitamin C which is keeping it from turning blue. Eventually the Vitamin C loses and, bam! - you get instant blueness.

Note: If you do not have liquid starch, you can also use 1/2 teaspoon of corn starch or potato starch. The liquids will be more cloudy and the reaction will happen a bit more slowly, but it’s still impressive.
Clean up: Carefully pour all liquids down the drain with plenty of water and wash your hands. Recycle the cups or dispose of them in the trash.


The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does the temperature of the water affect how quickly the liquids turn blue?
2. Does the amount of Vitamin C added (Liquid A) affect how fast the liquid turns blue?
3. Does stirring the liquids more affect how fast the liquids turn blue?

Plant Absorption

Materials you will need:

• Water
• Scissors
• Food Colouring
• Jar, Plastic Cup or Test Tube
• A Flower (light coloured-white carnation) or Celery Stalk (with leaves)

This is a colour changing experiment.

Steps:

1.  Fill the cup with water.
2.  Add a few drops of food colouring
3.  Cut the end off the stem (stalk)
4.  Put the flower in the water

Watch and in time the food colouring will be sucked up the stem along tiny tubes (called vessels) and the petals of the flower will start to change in colour.

Another way to try this experiment is to get a flower with a long, thick stem (or a celery stalk with leaves) and slit it carefully from the bottom and put one end in separate test tubes (with different food colourings).  Your flower (or celery) should have petals (or leaves) in two different colours.

Did you know that plants need water to live?  As well as absorbing water from the atmosphere (air) through their leaves, they suck water up through their stems.  If you used the celery stalk for the above experiment you could cut the stalk and see that the little holes inside are coloured.

Build a Film Canister Rocket

• One empty 35mm plastic film canister and lid. These are getting harder to find, but stores that develop film should have some. (The white canisters work much better than the black ones do.) If you have trouble finding canisters, you can get them HERE.
• One fizzing antacid tablet (such as Alka-Seltzer - Get this from your parents)
• Water
• Safety goggles

1. Put on those safety goggles and head outside - no really, when this works, that film canister really flies! If you want to try the indoor version, do not turn the canister upside down in step 5.
2. Break the antacid tablet in half.
3. Remove the lid from the film canister and put a teaspoon (5 ml) of water into the canister.
   Do the next 2 steps quickly

4. Drop the tablet half into the canister and snap the cap onto the canister (make sure that it snaps on tightly.)
5. Quickly put the canister on the ground CAP SIDE DOWN and STEP BACK at least 2 meters.
6. About 10 seconds later, you will hear a POP! and the film canister will launch into the air!
Caution: If it does not launch, wait at least 30 second before examining the canister. Usually the cap is not on tight enough and the build up of gas leaked out.

There's nothing like a little rocket science to add some excitement to the day. When you add the water it starts to dissolve the alka-seltzer tablet. This creates a gas call carbon dioxide. As the carbon dioxide is being released, it creates pressure inside the film canister. The more gas that is made, the more pressure builds up until the cap it blasted down and the rocket is blasted up. This system of thrust is how a real rocket works whether it is in outer space or here in the earth's atmosphere. Of course, real rockets use rocket fuel. You can experiment controlling the rocket's path by adding fins and a nose cone that you can make out of paper. If you like this experiment, try the Exploding Lunch Bag. Be safe and have fun!

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does water temperature affect how fast the rocket launches?
2. Does the size of the tablet piece affect how long it takes for the rocket to launch?
3. Can the flight path be controlled by adding fins or a nosecone to the canister?
4. How much water in the canister will give the highest flight?
5. How much water will give the quickest launch?