LESSON ONE
Observing Physical and Chemical Properties
Objective: Identify physical and chemical properties of substances.
Background: Bored during your summer vacation, you decide to go rock hunting. You have stumbled across what you think are five very elusive rocks; however, unfortunate though it may be, you cannot take them with you. Since you know matter can be described by its chemical and physical properties, you pull out your handy lab journal (stored behind your pocket protector) and write your observations. Luckily, you have a bottle of hydrochloric acid in your back pocket, so you can test the rocks' chemical reaction to the acid.
Use your superhero-like powers of observation and your fine-tuned senses to describe the rocks you tripped over. What physical characteristics can you describe with your senses of sight, smell, taste, sound, and touch. Scratch the rock for good luck; drop some acid on it, and watch what happens. Record your observations below:
Rock 1.__________________________________________________________
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Rock 2.__________________________________________________________
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Rock 3.__________________________________________________________
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Rock 4.__________________________________________________________
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Rock 5.__________________________________________________________
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Now, turn to page 36 and 37 of your textbook. What physical properties of matter are listed? Are your descriptions consistent with the definition of a physical property? ________________
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Did you observe any chemical properties? Describe._________
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(Samples used: sandstone, amazonite, shale, dolomite,
smokey quartz)
Lab: Separation of Mixtures
Objectives:
• Identify chemical and physical properties of substances;
• Relate knowledge of properties to the task of separating mixtures;
• Construct methods for separating items and implement procedure;
• Analyze results.
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Part I. Real Life Applications: Mining.
Materials: pictures of mine, rock samples from mine.
Background: Kyanite is a mineral containing the elements aluminum, silicon and oxygen; its chemical formula is Al2SiO5. When heated at very high temperatures, kyanite is converted to mullite, a compound with the chemical formula 3Al2O3«2SiO2. Kyanite and mullite are used in kiln furniture, electrical insulators, ceramics, and in nose cones of guided missals.
The largest kyanite mine is located in Willis Mountain in Buckingham County, Virginia. This mine produces 100,000 tons of kyanite annually; however, kyanite is not found alone. The metamorphic rock which contains the mineral kyanite also contains iron, quartz, mica, and pyrite. These by-products are isolated from the rock. The iron is sold to toy companies. Mica is used in metallic auto paint. Sulfuric acid, used in car batteries, is isolated from pyrite (also known as fool’s gold).
The unique chemical and physical properties of the different substances are used to isolate them. To recover the kyanite, iron, quartz, mica, and pyrite, the rock is crushed and the iron is removed with a magnet. The other substances are treated with chemicals and separated by density.
Remember: In a mixture, different kinds of matter can be separated physically because each component of the mixture retains its own composition and properties. Other properties are only observable when the substance interacts with another substance. These are its chemical properties.
Part II. Separation of Mixtures.
Problem. (Lab based on Holt Visualizing Chemistry)
Now that you have an idea of how a mixture may be separated and why a mixture may need to be separated, you will be given a mixture of poppy seeds, sand, salt, and iron filings that needs to be separated into its components. You must design the procedure to recover these substances.
Preparation.
1. List what you know about the physical and chemical properties of the substances.
2. List and describe known methods of separating mixtures.
3. Look at the below list of materials.
• distilled H2O • forceps • plastic forks
• sample of mixture • magnets • plastic spoons
• 8-well microstrip • paper clips • plastic straws
• aluminum foil • paper towel • rubber stoppers
• plastic wrap • petri dish or • tape
• cotton balls watch glass • test-tube holder
• filter paper • pipettes • test-tube rack
• test tubes • tissue paper • wood splints
4. Given your equipment, plan a workable procedure based on the physical and chemical properties of the substances in your mixture. Estimate length of time for each step. Copy the procedure into your lab notebook.
Technique
5. Obtain a sample of the mixture, a watch glass, a funnel and an 8-well microchemistry strip. Using the funnel place a small part of your sample in the first well of the strip for reference. You will need it for comparison of your separated components. Seal the opening of the first well with a piece of tape so the contents do not spill out.
6. Follow your planned procedure. Write down your observations and record your actions. When you have separated the first component from the mixture, place a small amount of it in the third well; seal it with tape. Leave the second well open.
7. As each component is separated, place small amounts in the fourth and sixth well; seal them with tape.
8. When all the components have been separated, ask your teacher to approve your samples.
Analysis
1. Write a paragraph summarizing your procedure. Rate your performance. Discuss recovery of each component in terms of purity and length of time it took to isolate the substance.
2. If you were to do this lab again, how would you change your procedure?
3. Name any materials or tools that were not available that might have made the procedure easier.
4. For each of the components, describe a physical property that allowed you to separate it from the rest of the mixture.
Possible Solution
1. Place mixture on paper towel.
2. Wrap magnet in plastic wrap.
3. Pass magnet through mixture.
4. Shake off loose non-iron particles.
5. Unwrap plastic; keep iron inside wrap. Fe is separated.
6. Place rest of sample in watch glass.
7. Add distilled water. Poppy seeds will float.
8. Remove seeds with plastic spoon.
9. Stir remaining mixture until salt is dissolved.
10. Fold filter paper and place in funnel.
11. Place funnel in test tube. Pass remaining mixture through funnel to remove sand.
12. Remove filter paper, and let it dry overnight. Sand is separated.
13. Place salt water in petri dish. Let water evaporate overnight. Remaining salt is separated.
Determination of Density
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Objectives:
• Calculate density from experimental measurements.
Background:
Density is mass per unit volume. The mass of any size sample of a substance divided by the volume of the sample will give the density of the material. A scientist, however, would not be satisfied with one measurement. A more accurate value is found by averaging the results of several trials.
Prelab:
1. Define accuracy, precision, uncertainty.__________________
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2. Write the formula for density. _________________________
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3. How do you find the mass of a solid object?_____________
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4. How could you find the volume of an irregularly shaped object? ____________________________________________________
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Materials:
• 3 different-sized samples of the same substance which could be 3 samples of metal shot or mineral samples
(smokey quartz, lead, iron)
• 100-mL graduated cylinder
• 30-mL beaker
• balance
• water
Procedure:
1. Measure and record the mass of the sample.
2. Fill a graduate cylinder 1/2 full with tap water and record this initial volume.
3. Tilt the graduated cylinder, gently add the metal. Measure and record this final volume.
4. Repeat procedure with each sample.
Data:
Record you data below. Calculate the displacement:
final volume -initial volume.
| Sample
Type |
Mass
(grams) |
Initial Volume
(cm3) |
Final Volume
(cm3) |
Displacement
(cm3) |
| Sample 1- A | ||||
| Sample
1- B |
||||
| Sample
1- C |
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| Sample
2- A |
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| Sample
2- B |
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| Sample
2- C |
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| Sample
3- A |
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| Sample
3- B |
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| Sample
3-C |
Analysis:
1. Use graph paper to make a graph of the above data placing the mass on the vertical axis and the volume on the horizontal axis. (Follow earlier directions for graphing.)
2. You will have 3 lines. Each line will connect data points for each substance.
3. Calculate the slope for each line on the of the above graph. Show your work. This value represents density. (Remember slope is Y2-Y1/X2-X1 or in this case M2-M1/V2-V1)
4. How many significant digits did you record in the density calculated for your trial? Explain how you decided on this number of digits.
4. Compare your results with the values given in the CRC Handbook of Chemistry and Physics or a rock and mineral handbook.
Calculate your experimental error.
value accepted - value measured * 100 = percent error
value accepted
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