LAB 2: MYSTERY BAG & REACTIONS IN A BAG

Transcription

1 LAB 2: MYSTERY BAG & REACTIONS IN A BAG APPLICATIONS OF THE SCIENTIFIC METHOD PURPOSE: To use the Scientific Method to make testable observations and carry out experiments to validate or challenge your initial hypothesis. BACKGROUND: Part I: What s in the Mystery Bag? Introduction: The main idea behind this activity is to understand the notion of scientific theories versus scientific facts. Different items have been placed into a Mystery bag and sealed. You are then asked to make educated guesses as to what items are in the bag based on smell, sound made by shaking the bag, and finally touch. These become the evidence that you gather to come up with educated guesses of the mystery items. This illustrates how scientists often cannot make direct observations of what they are trying to explain (e.g. origin of species, the structure of the atom), but by gathering evidence using different tools and methods (e.g. fossil records, gold foil experiment). Safety Observations: None in particular but in general treat unknowns as potentially harmful to you, with respect. Part II: Chemistry Reactions in a Ziploc Bag Introduction: It is in the observation of nature that all science finds its roots. To understand matter we must first observe it. Once you have made observations, you can formulate and test different hypothesis to explain what you have seen. In this second experiment, you will mix four substances in a sealable plastic bag and observe a reaction. It will be your job to determine which of the different components or combinations of those components are responsible for each of the observations. Safety Observations: Using safety goggles in this and all other experiments is required. All solutions in this activity can be diluted with water and flushed down the drain. Discussion of a Chemical Reaction Mystery: In this laboratory exercise you will investigate a chemical reaction involving 1. Sodium bicarbonate (NaHCO 3 ; baking soda, a common antacid) 2. Calcium chloride (CaCl 2 ; side walk salt, used medically to replace electrolytes) 3. Phenol red (an indicator used to diagnose kidney function) and 4. Water (H 2 O) When these four substances are mixed, a change occurs where the original substances (the reactants) get converted into different substances (the products) with completely different properties. This change is called a chemical reaction. Three significant changes may be observed when the above four substances are mixed. Lab 2: Rxn in a Bag and Mystery Bag (F15) GS

2 OBSERVATIONS: There may be changes in the: 1. Physical state, (solid, liquid, or gas) 2. Physical properties, (color) or 3. Heat energy a) If a chemical reaction gets warm we say that heat energy is released and the reaction is said to be exothermic. b) If a reaction gets cooler then heat energy has been absorbed and the reaction is endothermic. These observations should lead you ask specific questions to which we want answers. The questions we want to ask are: QUESTIONS: 1. What substance or combination of substances, (Sodium bicarbonate, calcium chloride, phenol red, and water) is responsible for the changes in the physical state observed? 2. What substance or combination of substances, (Sodium bicarbonate, calcium chloride, phenol red, and water) is responsible for the changes in the physical properties observed? 3. What substance or combination of substances, (Sodium bicarbonate, calcium chloride, phenol red, and water) is responsible for the changes in the heat energy observed? It is your goal to determine what is responsible for each significant change. This can be done by designing a series of experiments in which you change what substances are mixed. Try mixing only two or three substances rather than mixing all four. In performing your experiments you will gather results that you will tabulate in order to then make conclusions. PROCEDURES: I. MYSTERY BAG: 1. Obtain a sealed paper bag from your instructor, do not open it! 2. Place the bag on your work bench carefully and try to guess what is inside based on sight only, record your observations and guesses on the report sheet. (IIa) 1 3. Smell the bag without touching it and make new or modify your guesses on the report sheet (IIb) NOTES: 1 Our first guesses in science often are useful to set boundaries on the system, a full grown, live elephant can t be in the bag, right? 2 You should be able to make a more educated guess/hypothesis about our system. 4. Gently shake the bag and make new or modify your guesses on the report sheet. (IIc) 5. Finally you may touch and feel the items in the bag and refine your guesses on the report sheet. (IId) 2 Lab 2: Rxn in a Bag and Mystery Bag (F15) GS

3 PROCEDURES: II. REACTIONS IN A BAG 1. Put 1 spoonful of baking soda in one of the corners of a quart-sized Ziploc bag (this bag can be cleaned and reused through the rest of the experiment). Record the appearance on your record sheet. 2. Put 2 spoonsful of calcium chloride in the same bag but in a different corner. Record its appearance in your record sheet and then mix the two together by tipping the bag back and forth Measure 10 ml of phenol red solution. Place it into a small test tube or 10 ml graduated cylinder. 4. Place the small test tube inside the ziplock bag. Carefully squeeze out most of the air in the ziploc bag and then seal it Spill the phenol red solution out of its container by tilting the sealed ziploc bag. Mix the contents. Record your observations on the record sheet. (There should be three major observations). NOTES: 1 Does anything happen when they come in contact with each other? 2 If you don t remove the air from the large zip lock it has the tendency to burst during the reaction. 3 Remember when you want to figure out the role of a particular piece of the puzzle you must isolate it, see stared example 1 and 2 the only difference is the phenol red, whatever difference you see in the two systems must come from that missing element! 6. Design experiments to determine which substances are responsible for each of the 3 changes you observed. 3 Change only what substances you use in the reaction - do not change the amount of each substance. The following experiments might be tried: mixing calcium chloride and phenol red solution mixing calcium chloride and water mixing sodium bicarbonate and phenol red solution mixing sodium bicarbonate and water mixing sodium bicarbonate, calcium chloride, and water Lab 2: Rxn in a Bag and Mystery Bag (F15) GS

4 Lab 2: Rxn in a Bag and Mystery Bag (F15) GS

5 LAB 2: PART I MYSTERY BAG REPORT: NAME PARTNER DATE I. GROUP ACTIVITY: Arrange the following terms to complete the scientific method: Construct a Hypothesis Try again Report results (theory) Analyze data/make Conclusions Ask question Make observation Test with experiments True hypothesis False hypothesis Lab 2: Rxn in a Bag and Mystery Bag (F15) GS

6 Mystery Bag Group Observations A. Just look at the bag, don t touch or open. Group predictions: Class predictions: B. Smell the bag, do not touch. Group predictions: Class predictions: C. Gently shake the bag. Group predictions: Class predictions: D. Gently feel the bag and predict what is inside. Group predictions: Class predictions: 1. Based on your groups observations and the class discussion list with as much detail as you can everything in your bag. 2. I hate to break it to you but you cannot open the bag! Propose an experiment to prove the identity of one of the suspected mystery items. Lab 2: Rxn in a Bag and Mystery Bag (F15) GS

7 LAB 2: PART II REACTIONS IN A BAG NAME REPORT: PARTNER DATE II. A Chemical Reaction Mystery: Reactions in a Bag Trial 1 Materials Used 1) 1 Scoop Baking Soda 2) 2 Scoop Calcium Chloride 3) 10 ml Phenol Red + 4) water Observations of the reaction Trial 2 Trial 3 Trial 4 Trial 5 Continue with more trials as needed! Lab 2: Rxn in a Bag and Mystery Bag (F15) GS

8 Conclusions: Based on your data what combination of the 4 possible components [1) Sodium bicarbonate, 2) Calcium chloride, 3) Phenol Red, 4) Water ] is the minimum required for: A temperature change? Formation of a gas? Color change? How did you use the scientific method to make your conclusions What pitfalls or errors could have influenced your conclusions? Post lab Questions: 1. A. Given the two following statements, circle each statement that refers to a scientifically testable hypothesis. a) Chlorophyll makes grass green b) Earth rotates about its axis because living things need an alteration of light and dark B. Give a 1-2 sentence explanation as to why you chose the statement(s) you did. 2. In answer to the question When a plant grows where does the material come from? Aristotle hypothesized by logic that all material came from the soil. A. Is this hypothesis (circle one) correct, incorrect, partially correct? B. Propose (describe) and experiment to support your choice? Lab 2: Rxn in a Bag and Mystery Bag (F15) GS