Identifying an unknown substance lab

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EXPERIMENT 1: The Scientific Method Read the entire experiment and organize time, materials, and work space before beginning. Remember to review the safety sections and wear goggles when working with chemicals.

Allow at least 90 minutes for this experiment. Objectives: To systematically observe some properties of unknown substances and To use the Scientific Method to hypothesize about and identify unknown

substances. Materials: Student Provides: Distilled water Paper, clean white sheets Paper towels From LabPaq: Goggles Hand magnifying lens

Rubber stopper, #00 solid Spring scale, 10-g

Small plastic weighing bag Graduated cylinder, 50-mL Test tube rack Test tubes, 6 Test tube cleaning brush Wax pencil

Experiment Bag: Unknown substances, 6 Discussion and Review: To explain natural phenomena, scientists proceed in a carefully structured series of steps known as The Scientific Method. By conscientiously following these steps, scientists better ensure the validity of their work;: 1. Observe: Carefully observe the event or material. The observations may be made

directly with the human senses or indirectly with instruments. 2. Question: Formulate questions concerning observations made. These questions

usually include: What? How? When? Where? Why? Why is often the most difficult question to answer!

3. Hypothesize: Propose an answer to the questions. A hypothesis is an explanation

of the observed event or material based upon personal knowledge and other knowledgeable sources, and it is often an educated guess. A hypothesis should be testable, if possible, in a manner that will provide evidence that either rejects or supports the hypothesis and that can be duplicated by others.

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4. Experiment: Carry out an experiment in a set of controlled conditions to attempt to

provide evidence to support the hypothesis. A controlled experiment is a type of experiment consisting of two events or procedures that are identical in all but one aspect. The control group is used as a basis of comparison to the experimental group from which it differs by only the one variable. Experiments need to be replicable in order to produce sets of data that are meaningful in analysis.

5. Compile Data: Gather empirical data through experimentation and observation

and then compile and analyze it in order to determine if it supports or rejects the hypothesis. The two basic types of data are:

i.Quantitative: This is objective data that contains numbers and can be analyzed

statistically. Quantitative data is considered the superior data type because it is not easily biased.

ii.Qualitative: This is subjective data that includes attitudes, descriptions, and explanations of the phenomena studied per the perspective of the observer. Qualitative data is vulnerable to bias since it is cannot be precisely measured and does not contain verifiable numbers to be accurately analyzed by statistics.

. 6. Draw Conclusions: Review, evaluate and analyze the data gathered to arrive at a

conclusion that accepts or rejects the hypothesis. Acceptance may be within a range of confidence, rather than absolute acceptance or rejection. If the hypothesis is rejected, or if it is not accepted with a high level of confidence, one may repeat the steps of observation, questioning, hypothesizing, experimentation, and data collection to arrive at a new conclusion.

7. Publish: A scientist must make his/her observations, empirical data, and

conclusions available to other scientists for their review and acceptance or rejection. Submitting your laboratory report to your instructor is publishing, an important reason why the report should be done with care.

8. Form a Theory: A scientific theory is formed when a majority of the scientific

community supports and has confidence in the conclusion drawn from a hypothesis. 9. Establish a Law: A scientific law is established when a hypothesis is accepted as a

uniform and constant aspect of nature and there is no empirical evidence to prove otherwise.

PROCEDURES: In this experiment, you will apply the steps and logical framework of the Scientific Method. Through systematic observation, drawing of a hypothesis, and deliberate experimentation, you will try to identify the six unknown substances in the experiment bag marked Experiment 1. The unknowns are all substances often found in a typical home and none are toxic or dangerous. However, any unknown

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substance should be treated as potentially dangerous and handled accordingly until completely proven otherwise. While taste would be a good indicator for an unknown, scientist NEVER use a taste test on any unknown and neither should you!

1. Begin by setting up a data table as shown below to record your work observations.

Unknown A B C D E F Hypothesis

Color

Texture

Shape

Smell

Solubility

Density

Conclusion

2. Observe each of the containers of materials carefully. You may open the top of the

container to observe the unknown more closely, but be careful not to spill or remove any of the unknown from the container at this time. Reseal the container when you have finished your observation.

3. Your question for each unknown is “what is the material?”

4. Form a hypothesis about the identity of each unknown. Consider the general appearance of the unknown and hypothesize what household product it might be. Record your hypothesis and your principal reasons for the hypothesis in the table.

5. Decide on a protocol for the sequence of steps you will use to determine the identity of the unknown items. For example, in this experiment, density should be determined first because you will (1) use the full container of material and (2) you will know the volume of material in the container plus the weight of the container. Further, you should determined solubility last because it requires trying to dissolve the material in water. It

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will be difficult to continue to experiment with the material after it is mixed with water, especially in your limited laboratory facilities.

6. Set up an experiment in which you examine each unknown for the following

characteristics: a. Density

b. Color c. Smell

d. Texture e. Particle shape f. Solubility

Record quantitative data whenever possible and qualitative data when quantitative data is not possible. It is acceptable to provide both quantitative and qualitative data.

7. Work with only one unknown at a time and perform all of the following tests for each

one. Record your observations and then draw conclusions about the unknown’s identity. Complete the full series of tests for one unknown before starting to work on another. If you are still in doubt after performing all of the tests, read through the list of possible unknowns at the end of this experiment. Each of the unknowns is in that list.

8. Examine each unknown for each of the following characteristics: Density: Each unknown is packaged in a plastic container that, when full as each should be, contains exactly 1.5 cc (cubic centimeters) of material. Place the container of unknown in the small plastic bag provided and suspend it from the scale. Hold the scale steady at eye level until it stops moving and read and record the weight. Note: Be sure to calibrate the scale before using it. See calibration instructions on the box. Then calibrate the scale plus weighing bag before continuing. Fold a 10-cm square of clean white paper in half and open it so that it has a crease down the middle. Open the container and pour the contents of the container of unknown onto the center of the paper. Tap the container sharply on the paper to ensure that all of the contents are emptied. Place the empty container back in the plastic bag and weight it as before. Subtract the weight of the empty container and bag from the weight of the full container and bag. The difference between the two weights is the weight of the unknown in grams. Divide the weight of the unknown in grams by the known volume of the container, 1.5 cc. The quotient represents the density of the unknown in g/cc (grams per cubic centimeter). This density measure should fall somewhere in the range of 0.5 to 1.5 g/cc. Recall that the density of water is 1 gm/cc, and think about how dense these materials are relative to water. Color: Note the color and related visual aspects of the unknown. Is it shiny or dull in reflection or does it have any luminescence or color shift as does a hologram?

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Texture: Take a pinch of the material and rub it between your fingers. Observe how it feels to the touch. Is it gritty or smooth, dry or oily, etc.? Note: if you had not been told the substances were non-toxic, you would wear gloves to test the texture. Particle shape: Observe the material on the paper with the hand lens. If the unknown is a powder or granular, observe the shape of the particles. Note if the individual particles are too small to see or, if they are visible, are they smooth or sharp edged, regular or irregular, crystalline or amorphous? Smell: Prepare to smell the unknown the way a scientist does. To avoid inhaling potentially dangerous fumes or powders, partially fill your lungs with air, and, while holding the paper in front of you, use your hand to waft the odors gently toward your nose. Then lightly sniff the fumes in a controlled fashion. NEVER INHALE FUMES DIRECTLY! Observe if the unknown smells sweet or sour, chemical or organic, or is in some other way, known to you. Can you hypothesize the identity of the material from the smell? Solubility in water: Place approximately half of the unknown material in a clean, dry test tube. Measure out 5 cc of distilled water into the graduated cylinder and pour it into the test tube. Stopper the test tube with a clean dry rubber stopper and shake vigorously.

Soluble material will disappear after shaking and the water will be clear, not cloudy. If the water does clear, observe if it has any color.

Insoluble material will not disappear in the water

and the water will have a cloudy appearance after being shaken. If the unknown goes into suspension, the water will remain cloudy after several minutes. If it is not in suspension, the material will settle to the bottom and the water will clear.

After observing, use the wax pencil to write the letter of the unknown’s on the test tube before placing it in the test tube rack for further observations. Remove, wash, and dry the rubber stopper before testing the next unknown.

9. Repeat the above procedures for each of the five remaining unknowns. Record your observations for each in the data table you prepared at the beginning of this lab.

10. Allow the test tubes to sit undisturbed in the rack at least one hour but preferably longer or over night. Record your observations. Has anything happened to change your mind about previous observations and/or conclusions?

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Questions: A. Which of the six measures in the experiment give you quantified data? B. For which of the unknowns was your conclusion the same as your hypothesis? C. Were any of your conclusions different from your original hypothesis? If so, what

particular factor(s) changed your mind? D. What is your level of confidence (0 – 100%) in your conclusion for each unknown? Cleanup: Although not hereafter repeated, clean up for this and all other experiments is as follows:

Carefully blot up with disposable paper towels any remaining chemicals or materials or pour the chemical mixtures down the sink and rinse with a lot of water.

For any remaining chemicals that will not be further used, squeeze their pipets or containers and allow the chemicals to flow down a sink drain; then flush the drain with lots of water. Throw the empty chemical containers in the garbage.

If you wish to reseal any pipets for later use - though not applicable to this experiment - do so with a heated knife blade. Heat the blade of an old knife over a heat source until red hot. Then briefly press the pipet tip against the side of the blade while turning the pipet back and forth between your fingers. NEVER USE A DIRECT FLAME TO SEAL A PIPET OF CHEMICALS!

Thoroughly clean all beakers, test tubes, and other equipment with the test tube cleaning brush and soapy water. Use distilled water for a final rinse and dry with paper towels. Properly pack and safely store your LabPaq and all equipment away from the reach of children and pets.

Wash your hands with soap and water and similarly clean your work area.

List of Possible Unknowns:

Alka Seltzer® Baby powder Baking soda Cornstarch Cat litter Coffee

Flour Jell-O® powder Plant fertilizer Potting soil Powdered milk Powdered Sugar

Salt Sand Scouring powder Sugar Tooth powder Unrefined sugar