LAB 1B: THE SCIENTIFIC METHOD: MAKING OBSERVATIONS & DESIGNING EXPERIMENTS

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1 LAB 1B: THE SCIENTIFIC METHOD: MAKING OBSERVATIONS & DESIGNING EPERIMENTS PURPOSE: To practice the scientific method of observation, hypothesis, experimentation, & conclusion. SAFETY CONCERNS: Always wear safety goggles. SCIENTIFIC METHOD: As we observe the world and how it works, questions arise to which we would like answers or explanations. For example you may have made the following observation: OBSERVATION: The common disinfect, hydrogen peroxide, bubbles when it comes in contact with a wound. This observation may lead you wonder about the behavior and properties of hydrogen peroxide. From our observations we can devise specific questions to which we want answers. There are a number of questions you might ask, for example: POSSIBLE QUESTIONS: What environment(s) enable hydrogen peroxide to form bubbles? Does hydrogen peroxide form bubbles with all wounds or just fresh ones? What is the composition of hydrogen peroxide? What is the composition/identity of the bubbles formed? What is present in a wound that is not present in healthy skin? Does the temperature influence the formation of bubbles from hydrogen peroxide? Let s choose one of these questions to deal with: QUESTION: What environment(s) enable hydrogen peroxide to form bubbles? The first step in answering a question is proposing a hypothesis. A hypothesis is an educated guess to give an explanation, or answer a question, based on experiments you, or someone else, have already done. In regards to our question about the bubbling of hydrogen peroxide we can state a hypothesis based on what we ve already learned either from previous experimentation or our past experiences. HYPOTHESIS: I think blood must be present for hydrogen peroxide to form bubbles. RATIONALE: I believe this because when I have put hydrogen peroxide on a wound containing fresh blood bubbles have formed. But when I put hydrogen peroxide on healthy skin no bubbles formed. To answer a question with more confidence than just an educated guess, tests or experiments must be designed and performed to justify the answer. The experimental procedures must be clear enough to be followed and specific enough to achieve unambiguous results. EPERIMENT: Procedures: 1. Obtain as many samples as possible of substances on which to test the bubbling potential of hydrogen peroxide. For example; a fresh wound, an old would or scab, healthy skin, wood, piece of cut potato, piece of cut onion, aluminum foil, platinum metal others 2. Maintain each sample at room temperature. 3. Place a couple of drops of commercially available hydrogen peroxide solution (3% H 2O 2) onto each sample available. What to observe: 4. Watch for any bubbles produced that would indicate an environment conducive to bubble formation. CH104 Lab 1B: The Scientific Method (F15) 7

2 By experimentation we gather firm evidence or results that we can use to either prove or disprove the hypothesis. RESULTS: Substance to Test Bubbles formed? Yes No Wound with fresh blood Wound with dried blood Healthy skin Wood Cut raw potato Cut raw onion Aluminum foil Platinum Experiments must provide enough evidence to eventually allow reasonable conclusions about whether or not the initial hypothesis was correct. Often multiple experiments must be performed to be certain that the results are repeatable. Sometimes the hypothesis must be revised and then tested repeatedly until confident conclusions can be made. Notice the modifications in the following: CONCLUSION: Hydrogen peroxide will form bubbles whenever blood is present but blood is not essential for bubble formation. RATIONALE: My experiment showed that hydrogen peroxide forms bubbles when dropped on either fresh or dried blood but also forms bubbles when in contact with raw potato, raw onion, and platinum metal which do not contain blood. When designing any experiment the potential for errors must be taken into account. Errors occur whenever any kind of measurement is made as well as when sloppy technique is used. It is impossible to avoid all errors. Each error must be recognized and considered whenever conclusions are made. ERROR ANALYSIS: Although all tests were done at room temperature (25 o C) the bloody wounds and healthy skin were at body temperature (37 o C). To avoid this difference perhaps one or more of the following modifications could be made: a drop of blood at room temperature could be dropped into a sample of peroxide at room temperature. a sliver of dead skin at room temperature could be used instead of skin on a living body. Other samples could be brought up to 37 o C before being tested with the peroxide. Often, when we do research to answer one question, many more questions arise. One experiment can therefore lead to many more. Examples of Further Questions that arise from our peroxide experiment could be: FURTHER QUESTIONS: What is the substance in blood that causes hydrogen peroxide to bubble? Do raw potato and raw onion contain the same substance that is present in blood? Would a cooked potato cause hydrogen peroxide to bubble? 8 CH104 Lab 1B: The Scientific Method (F15)

3 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. OBSERVATIONS: There may be changes in the: physical state, (solid, liquid, or gas) physical properties, (color) or heat energy o o If a chemical reaction gets warm we say that heat energy is released and the reaction is said to be exothermic. 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: What substance or combination of substances, (Sodium bicarbonate, calcium chloride, phenol red, and water) is responsible for the changes in the physical state observed? What substance or combination of substances, (Sodium bicarbonate, calcium chloride, phenol red, and water) is responsible for the changes in the physical properties observed? 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 different 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. CH104 Lab 1B: The Scientific Method (F15) 9

4 PROCEDURES: ACTIONS: I. CHEMICAL REACTION MYSTERY 1. Obtain a quart-sized zip-close plastic bag. 2. Place 1 spoonful of sodium bicarbonate 1 (NaHCO 3 ) into one of the corners of the plastic bag. Observe and record its properties 2 on the report sheet (Box I2). 3. Place 2 spoonfuls of calcium chloride 3 (CaCl 2 ) in a different corner of the same bag. Note and describe the properties 2 of the calcium chloride (Box I3). 4. Mix the sodium bicarbonate and calcium chloride together by gently tipping the bag back and forth. 5. Measure 10 mls of 0.04% phenol red solution and pour into a small test tube or vial. Note and describe the properties. (Box I5) Without spilling, set the small test tube or vial inside the zip-lock bag. Without spilling the vial, carefully squeeze most of the air out of the bag and seal it With all of your ingredients sealed inside the bag now spill the phenol red solution by tipping over the tube. Mix the contents of the bag. This is Trial Observe the chemical reaction occurring between the 4 substances inside the bag and record your observations of the 3 significant changes. (Box I8). 9. Perform further trials by making new combinations of the 4 possible substances to determine which substances are responsible for each of the 3 changes you observed. 6 Change only what combination substances you use in the reaction. Do not change the amount of each substance Record your observations for each trial in the results column of the report sheet. NOTES: 1 Sodium Bicarbonate is common baking soda. 2 Physical properties may include its state (whether it is solid, liquid, or gas), its color, its odor, etc. If it is a solid note the kind of granules or crystals present that might distinguish it from other solids. 3 Calcium Chloride is a commonly used salt for melting ice on frozen sidewalks. 4 Phenol red solution is a combination of phenol red (a solid) and water. 5 The bag must be sealed well so that no liquid or gas escapes. 6 Use the same bag but clean the zip-close bag and vial before doing a new experiment. Rinse the bag with water several times and pour the water down the drain. Dry the inside of the bag with a paper towel. Do not puncture the bag. Rinse the tube or vial. 7 Phenol Red solution always contains water so you will never use phenol red without using water as well. However, you can use water without using phenol red by simply using deionized water as one of your reagents. 11. Do as many trials as needed to discover the minimum combination of substances needed to produce each change. II. CONCLUSIONS 12. Make conclusions to answer the questions as to the minimum substances necessary to produce each property change. 13. Clean-up by rinsing the zip-close bag in the sink. 10 CH104 Lab 1B: The Scientific Method (F15)

5 LAB 1B: THE SCIENTIFIC METHOD REPORT: NAME PARTNER DATE I. CHEMICAL REACTION MYSTERY Trial # 1 1. sodium bicarbonate Reagents to Mix Properties of Reagents Results after Mixing Describe any Changes in: (NaHCO 3 ) 2. calcium chloride (CaCl 2 ) 3. phenol red and 4. water (H 2 O) I2 I3 I5 I8 A. Physical State Change: C. Heat Energy Change: Trial # Experiment: (Reagents to Mix) Results: After Mixing describe any Changes: If no change occurs mark in the space. 2 A. Physical State change: 3 A. Physical State change: 4 A. Physical State change: 5 A. Physical State change: 6 A. Physical State change: CH104 Lab 1B: The Scientific Method (F15) 11

6 II. SUMMARY AND CONCLUSIONS: QUESTIONS: A. What substance or combination of substances is responsible for the change in physical state? (state the change. ) B. What substance or combination of substances is responsible for the change in color? (state the change. ) C. What substance or combination of substances is responsible for the change in the heat energy? (state the change. ) CONCLUSIONS: Circle the minimum items required to make the effect. sodium bicarbonate (NaHCO 3 ) phenol red calcium chloride (CaCl 2 ) water (H 2 O) Circle the minimum items required to make the effect. sodium bicarbonate (NaHCO 3 ) phenol red calcium chloride (CaCl 2 ) water (H 2 O) Circle the minimum items required to make the effect. sodium bicarbonate (NaHCO 3 ) phenol red calcium chloride (CaCl 2 ) water (H 2 O) Explanation: How did the use of the scientific method enabled you to make proper conclusions? Error Analysis: Other than human error account for any potential pitfalls or errors possible in this experiment even if you didn t make them. Further Question(s): Come up with some questions inspired by this lab experience that might generate future experiments. RELATED EERCISES: 1. A hypothesis is A. an educated guess. B. the answer to a question. C. an experiment to perform. Reference Search: 2. Use the Merck Index to answer the following questions about phenol red. A. List an alternate chemical name B. List the percent composition of it s elements: Carbon (C) % Oxygen (O) % Hydrogen (H) % Sulfur (S) % 12 C. List any medicinal or therapeutic use CH104 Lab 1B: The Scientific Method (F15)