OBSERVING A CHEMICAL REACTION INTRODUCTION Just as in all experimental science, the science of chemistry is based upon observation. In this experiment, you will observe a chemical reaction. It is unlikely that you will understand all that is happening, but, at this time, it is not necessary that you do. Rather the purpose of this experiment is to give you practice in distinguishing observation from inference. An observation is a statement of fact, based on sensory data. An inference is a judgement or opinion about what is observed. A statement such as "the liquid is clear and colorless" is an observation. It would be an inference to say, without further testing, that the clear and colorless liquid is water. As you observe the reaction in this experiment, try to make as many observations as possible. Be aware that a quantitative observation is an observation that involves a measurement. A qualitative observation is a general description and does not involve a measurement. "The liquid is hot" is a qualitative observation. "The temperature of the liquid is 95.0°C” is a quantitative observation. OBJECTIVES 1. To make as many observations as possible of a chemical reaction. 2. To learn to distinguish between observations and inferences. 3. To learn to distinguish between qualitative and quantitative observations. MATERIALS Copper (II) chloride dihydrate (CuCl22H2O) Aluminum Foil EQUIPMENT 1 50-mL beaker 1 thermometer 1 plastic spoon 2 pair safety goggles SAFETY 1. Wear safety goggles. 2. Handle the thermometer carefully. Do not try to balance it propped up in the beaker. Do not use a thermometer as a stirring rod. Mercury is extremely toxic and a mercury spill is difficult to clean up. If you break a mercury thermometer report it to the teacher so that the mercury can be cleaned up thoroughly and disposed of properly. 3. Copper(II)chloride is an irritant. Avoid skin contact with this chemical. Wash your hands thoroughly after use. PROCEDURE As you perform the experiment, record your observations in the table. 1. 2. 3. 4. 5. Obtain a sample of Copper (II) chloride dihydrate, CuCl22H2O 4. Describe the crystals in as much detail as you can, and make as many observations as possible. Fill the 50-mL beaker about one-half full to tap water. Without stirring add one-half teaspoon of crystals to the water. Record you observations of the mixture. Observe both the crystals and the water. Stir the mixture with the spoon until the crystals are completely dissolved. Record your observations of the solution. Place a thermometer in the copper(II)sulfate solution and note the temperature. Then, crumple the aluminum foil into a loose ball and add it to the solution in the beaker. CAUTION: OBSERVE THE MIXTURE FROM THE SIDE. DO NOT LOOK DIRECTLY DOWN INTO THE BEAKER. Continue to observe the mixture for at least 10 minutes and note any change in temperature. Does stirring the mixture have any effect on the reaction? When the reaction is complete, pour off the liquid portion of the mixture into the sink. Discard the solid contents of the beaker into the chemical waste container provided by your teacher. Wash and dry the equipment that you used. Wash your hand thoroughly before leaving the laboratory. Name________________________________________________Period_____Date__________ OBSERVING A CHEMICAL REACTION DATA TABLE: OBSERVATIONS System Observation Dry Copper(II)chloride Copper(II)chloride in water (before stirring) Copper(II)chloride (after stirring) Copper(II)chloride solution plus nail Initial Temperature Final Temperature Analysis of Observations: 1. Check your observations. Eliminate any that are inferences rather than observations by drawing a single line through them. 2. Prepare a list of all your observations, stated in complete sentence form. Divide the list into four sections: observations of the dry crystals, observations of the wet crystals before stirring, observations of the solution before the addition of the nail, and observations of the reaction that occurs when the nail is added to the solution. Use your own paper. Number the observations consecutively. Circle the number of any observation that is quantitative. 3. Write down your inference of what happened in this reaction. Explain how your observations led to your hypothesis.