Chemical Reaction Lab Bagged Chemical Reactions

Transcription

1 Learning Target: The student experiments and determines that the rates of reaction among atoms and molecules depend on the concentration, pressure, and temperature of the reactants and the presence or absence of catalysts. Background: Chemical reactions occur when molecules come together to form new products. In our bodies and environments, chemical reactions occur continuously to help run our lives. During a reaction, chemical bonds are broken and remade. Usually, color changes, gases being released, changes in temperature, and/or formation of a precipitate (solid chunks) characterize chemical reactions. These events describe changes in energy or solubility of the compound, meaning new products were produced. Chemical reactions can be defined by a chemical equation in which reactants and products are characterized by chemical symbols. All chemical reactions are accompanied by a change in energy. Some reactions release energy to their surroundings (usually in the form of heat) and are called exothermic. For example, sodium and chlorine react so violently that flames can be seen as the exothermic reaction gives off heat. On the other hand, some reactions are need to absorb heat from their surroundings to proceed. These reactions are called endothermic. A good example of an endothermic reaction is what takes place inside an instant cold pack. Commercial cold packs usually consist of two compounds urea and ammonium chloride in separate containers within a plastic bag. When the bag is bent and the inside containers are broken, the two compounds mix together and begin to react. Because the reaction is endothermic, it absorbs heat from the surrounding environment and the bag gets cold. Purpose: Observe the changes associated with a chemical reaction including heat changes, changes in an indicator, bubble of gas released. Determine which compounds are reactants and which are products through the use of a chemical equation. Use indicators in order to identify whether a solution is acidic or basic. Safety: NO eating or drinking during the lab; the chemicals should NOT be ingested. If accidentally ingested drink lots of water and contact a medical facility. CO 2 is produced in the bags, release the gas carefully so your bag does not explode. Dispose of bags in trash, AFTER taking the test tubes out.

2 Materials (Per Group): safety goggles 4 tablespoons Calcium Chloride Pellets (CaCl 2 ) 2 tablespoons Baking Soda (Sodium Bicarbonate, NaHCO 3 ) Phenol red solution graduated cylinder 4 test tubes 2 plastic spoons four 1 gallon ziploc type bags 2 rubber bands water Procedure: Experiment 1 1. In a Ziploc type of bag, place 2 tablespoons of sodium bicarbonate (Baking Soda). 2. Measure 30ml of water in the graduated cylinder. Pour the water into a test tube. 3. Add 3 drops of Phenol red indicator to the test tube. 4. Place the test tube in the bag in the upright position. DO NOT TIP TEST TUBE YET! 5. Squeeze the excess air and seal the bag. 6. Spill the water into the bag and record observations in the chart provided. Make sure to feel the outside of the bag! 7. Take test tube out of bag when done, throw bag in trash. Experiment 2 1. In a new Ziploc type of bag, place 1 tablespoon of calcium chloride. 2. Measure 30ml of water in the graduated cylinder. Pour the water into a new test tube. 3. DO NOT ADD ANY PHENOL RED 4. Place the test tube in the bag in the upright position. DO NOT TIP TEST TUBE YET! 5. Squeeze the excess air and seal the bag. 6. Spill the water into the bag and record observations in the chart provided. Make sure to feel the outside of the bag! 7. Take test tube out of bag when done, throw bag in trash.

3 Experiment 3 1. In a new Ziploc type of bag, place 2 tablespoons of Calcium Chloride in one corner of the bag. Twist off that corner to separate that chemical from the rest of the bag and tie with a rubber band. 2. In the OPPOSITE corner of the bag, place 2 tablespoons of Sodium Bicarbonate (Baking Soda).Twist off that corner to separate that chemical from the rest of the bag and tie with a rubber band. 3. Measure 30ml of water in the graduated cylinder. Pour the water into a new test tube. 4. DO NOT ADD ANY PHENOL RED 5. Place the test tube in the bag in the upright position. DO NOT TIP TEST TUBE YET! 6. Squeeze the excess air and seal the bag. 7. Carefully cut the rubber bands from the 2 corners while a group member holds both corners apart. DO NOT CUT THE BAG! 8. Release the corners and spill the water into the bag (mixing all 3 chemicals together) and record observations in the chart provided. Make sure to feel the outside of the bag especially at each corner! 9. Take test tube out of bag when done, throw bag in trash. Experiment 4 1. In a new Ziploc type of bag, place 2 tablespoons of Calcium Chloride in one corner of the bag. Twist off that corner to separate that chemical from the rest of the bag and tie with a rubber band. 2. In the OPPOSITE corner of the bag, place 2 tablespoons of Sodium Bicarbonate (Baking Soda).Twist off that corner to separate that chemical from the rest of the bag and tie with a rubber band. 3. Measure 30ml of water in the graduated cylinder. Pour the water into a new test tube. 4. Add 3 drops of Phenol red indicator to the test tube. 5. Place the test tube in the bag in the upright position. DO NOT TIP TEST TUBE YET! 6. Squeeze the excess air and seal the bag. 7. Carefully cut the rubber bands from the 2 corners while a group member holds both corners apart. DO NOT CUT THE BAG! 8. Release the corners and spill the water into the bag (mixing all 3 chemicals together) and record observations in the chart provided. Make sure to feel the outside of the bag especially at each corner! 9. Take test tube out of bag when done, throw bag in trash. WASH OUT ALL TEST TUBES. Clean up lab station so it looks like you found it.

4 Observations/Data Analysis: 1. Which steps could be characterized as physical change? Chemical change? Explain your reasoning. 2. What observations confirm the presence of a chemical change? 3. Which process(es) would you characterize as exothermic? EXPLAIN. 4. Which process(es) would you characterize as endothermic? EXPLAIN. Conclusion: 1. Phenol red is an indicator dye, used as an acid ph indicator with a transition point of 7.5 (acidic side to yellow / basic side to red). What does that tell us about each bag? 2. Balance the chemical equations used to describe the reactions. NaHCO 3 (s) + CaCl 2 (s) CaCO 3 (s) + NaCl(aq) + HCl(aq) NaHCO 3 (s) + HCl(aq) H 2 O(l) + CO 2 (g) + NaCl(aq)

5 3. Give the names of all the compounds present in the chemical reaction you observed. (HCl is hydrochloric Acid, you will learn how to name acids in chemistry) NaHCO 3 CaCl 2 CaCO 3 NaCl H 2 O CO 2 4. What type of gas is in your bags? Explain how you know? 5. Propose an explanation for where the energy change originated. 6. Which chemistry law can you confirm in this investigation?