Retrieved from the Akron Global Polymer Academy at http://www.agpa.uakron.edu/p16/lesson-plans.php
Author: Joyce Brumberger
Students will learn, through the creation of their handmade hydrometer, how a hydrometer functions and what it measures. Using their hydrometer, they will determine the relative differences in specific gravity of liquids and compare these values to those obtained from a commercially manufactured hydrometer. Based on their findings, students will create their own liquid density column.
What should the students know as a result of this lesson?
What should the students be able to do as a result of this lesson?
Short Clip Videos as described in Engagement Phase
Exploration and Elaboration:
20 oz water bottles with tops cut off, 1 for each liquid used, 7 bottles/set - 1 set/group
2 2-L bottles
3 oz. plastic drinking cups
Isopropyl alcohol (purchased at pharmacy)
Select one oil:
Corn oil, Olive oil, Baby oil
Materials for hydrometer: To be made by each student
Permanent markers- 2 different colors
Small nails to fit inside straw
Plasticine or blu-tac
25 mL graduated cylinder
3 x 5 index cards
Universal hydrometers, 1 for each group (Nasco Science, 1-800- 558-9595 - item #SB16439M /$7.40 each)
(hydrometer can be shared between groups if necessary)
Glass or plastic container for disposal of liquids in density columns
Hydrometers of varying types for:
Show a video of someone trying to start the car, but the battery is dead.
Ask students, "Have you or someone you know had a similar experience?" Most will say yes. Ask students, "Do you know that a car battery has fluid in it that can be checked to insure it is in good working order?" Answers will vary.
Play the video clip that will show how to use a device to check the fluid levels in a car battery. http://video.aol.com/video-detail/auto-and-truck-battery-reconditioning-step-5/1607610001
Assessment is ongoing with verbal responses from students.
Assessment is ongoing as students work together, record data, and discuss findings with each other.
Ask students the following questions:
Responses will vary, but most will find that it was difficult to get an accurate measurement. Some may discuss difficulties they had with the instrument staying upright or other faulty behavior.
Responses will vary, but most will say that the manufactured device provided more accurate measurements and was easier to use. The two instruments were similar because they both floated up or down depending on the liquid substance used.
The instrument is a hydrometer and its function is to determine the specific gravity of a substance.
Specific gravity is similar to the density of a substance, but it has no units of measure. This is because specific gravity is a comparison of the density of a substance to the density of water. The specific gravity of water is given the value of 1.000 when the temperature of the water is 60 degrees F.
The water was at room temperature and the value of 1.000 is given when the water is 60 degrees F. Slight differences may have been seen.
Tap water has minerals in it, unlike distilled water. Demonstrate this by placing the hydrometer in a sample of each separately and have a volunteer come up to read the values.
The specific gravity is not the same because of the fat content in the milk. However, there are many components of milk and the fat content has to be determined with other methods.
Responses will vary, but a common problem is that some substances mixed together such as saltwater and sugar water or alcohol. This is a good example that can later lead into discussion of solutions.
Having seen the videos, students will respond that hydrometers are used to check car batteries. Hydrometers are also used for checking antifreeze level in car radiators, salt water fish tanks, wine and beer making, testing milk, and for specific needs in many other industries. When they get a urine test at the doctor's office, the urine strips are providing a specific gravity value. The normal range is between 1.020 -1.030. Values higher or lower than that may indicate that the body is not functioning normally and the doctor can begin to do other tests to make a proper diagnosis.
Show samples of other hydrometers that were collected for this lesson.
A hydrometer floating in the tank will provide a specific gravity value. You then have to use a special chart that compares the temperature of the water and the specific gravity value to find the salinity level.
Add any of the substances that increased the specific gravity of water such as sugar or salt.
Assessment is ongoing with oral responses and discussion of questions.
The density columns will reflect student understanding and oral discussion will reveal things that were correct or that could be improved in the future.
Understand the concept of density.
Lesson "Float Your Boat" - optional
Hydrometers are calibrated, cylindrical glass tubes that are weighted with lead shot or mercury and are used to find the specific gravity of a liquid. Specific gravity is the ratio of the density of a liquid compared to the density of water at 60 degrees F. There are no units of measure associated with it because it is a comparison. For example, the density of water at 60 degrees F is 1.000 g/cm3. Its specific gravity is 1.000. The density of ammonia is .8974 g/cm3. Its specific gravity compared to water is .8974, which means that it is lighter than water.
The hydrometer is lowered into a tall column of the liquid to be measured and allowed to float upright. A reading is taken off the hydrometer at the point at which the surface of the liquid touches the glass stem. Hydrometers function on the basis of Archimedes' Principle. When the hydrometer is placed in a tall column of liquid, the liquid is buoyed up by a force proportional to the weight of the displaced liquid. Hydrometers float lower in low density liquids and higher in high density liquids.
There are universal hydrometers, but in various industries the range of specific gravity for liquids they use is very small. Therefore, hydrometers are designed for large values or small values.
Density is a concept that is very conceptual and many hands-on examples and experiences help to foster better understanding. A common misconception is that density applies only to solids when, in fact, it applies to liquids and gases as well. The density of a liquid when compared to water is called specific gravity. Specific gravity of liquids is a measure constantly used in industry, but it is also used very commonly in our everyday lives from checking proper levels of car battery and radiator fluids to urine tests at the doctor's office.
Grouping Suggestions: Try to insure that all students have participated and expressed their ideas either verbally or through written comments. When working in pairs or groups try to make the groups as heterogeneous as possible being sensitive to specific needs of individuals.
Engagement: 10 minutes
Exploration: 25 minutes
Explanation: 20 minutes
Elaboration: 30 minutes
Liquid Measurement Data Table and Worksheet
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