CHEMICAL REACTIONS 345

TOPIC 4 . CHEMICAL REACTIONS

ILLUSTRATIVE EXPERIMENTS

• Keep demonstration simple and eye catching

• Do not overlook simple demonstrations. Even trivial activities can spark all sorts of interesting ideas.

• Involve your audience as much as possible; use your students as assistants

• Rehearse the demonstration before hand.

• Demonstrations are not replacements for practical work, but they make good extensions to a topic and help prompt discussion.

• The most important part of a good demonstration is that the students enjoy it.

PHYSICAL VS CHEMICAL

"REACTIONS IN A BAG" EXPERIMENTS

EXPERIMENT 1:

MAKE YOUR OWN INSTANT COLD PACK (PHYSICAL)

The process in making the cold pack is not a chemical reaction but merely the physical act of dissolving. When ammonium nitrate is dissolved in water, the process is endothermic, thus producing the cold pack.

You will need: Ammonium nitrate, tap water, zip lock bag (sandwich size), graduated cylinder

1. Weigh out 25 grams of ammonium nitrate directly into a one-quart size Ziplock plastic bag.

2. Using a graduated cylinder, measure out 50 mL of water.

3. Quickly, pour the water into the bag of ammonium nitrate, and seal the bag (try and remove excess air before sealing the bag.)

4. Gently squeeze the bag to mix the solid and water.

5. Let the students feel the bag. It becomes cold within seconds and will remain cold for about 20 minutes.

EXPERIMENT 2:

CALCIUM CHLORIDE: A REACTION IN A BAG. (CHEMICAL)

Introduces students to a chemical reaction involving a color change, the formation of a gas and heat changes from hot to cold. The students can actually hold this chemical reaction in their hands to see and feel the reaction take place.

The acid-base indicator will change colors (from basic to acidic). For example: phenol red solution goes from red to orange to yellow. Universal indicator solution starts out green and changes to pink. Cabbage juice, changes from blue-green to purple to pink. The plastic bag will also inflate due to the formation of carbon dioxide gas.

You will need: calcium chloride, Sodium Bicarbonate (baking soda), Acid-Base indicator (any kind), Ziplock sandwich bags, spoons, graduated cylinder

1. Place one spoonful of calcium chloride into a plastic sealable bag.

2. Place 1 spoonful of sodium bicarbonate into the bag. Seal the bag, shake it and see if a chemical reaction takes place.

3. Measure 10 ml (or 2 teaspoons) of indicator solution. Carefully add it to the bag. Flatten the bag to remove the air and seal it.

4. Tilt the bag back-and-forth to wet all of the solid. Squeezing the bag may also help in wetting the solid. Be careful not to squeeze the bag too hard as it might break or open up.

5. Observe the reaction. If the bag gets tight due to pressure, open the seal to release the pressure then reseal it.

6. Answer the following:

a.) How was this experiment different then the one before?

b.) Did a noticeable reaction occur before the indicator solution was added?

c.) What color change did the indicator go through?

d.) Why does the bag inflate?

e.) Does the reaction get hot or cold initially?

f.) Does the reaction get hot or cold after 1 minute?

g.) What observations did you make that tell you a chemical reaction is taking place?

h.) Was this experiment a physical or chemical reaction?

Investigation sheet Experiment 1

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