Density of various liquids demonstration

Hernan Mejia

SL 525 CSUN

Dr. Norm Herr

Fall 2010

Title: Demonstrating the Density of Liquids

Principles Investigated: DENSITY = MASS/VOLUME

· The mass density of a material is defined as its mass per unit volume.

· Density is a physical property of matter.

· Each element and compound has a unique density associated with it.

· An object’s buoyancy is determined by its density in relation to the density of the surrounding liquid.

· In liquids, because its particles are free to move, a liquid has no definite shape; however it does have a definite volume

Misconception:

Students may think that mass and volume are the same physical property. Through the density of various liquids demonstration that follows, I will demonstrate that mass and volume are two different properties of matter. They are two related, but different things.

Standards:

Investigation and Experimentation (from CA Content Standards)

7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:

a. Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.

b. Use a variety of print and electronic resources (including the World Wide Web) to collect information and evidence as part of a research project. c. Communicate the logical connection among hypotheses, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence. d. Construct scale models, maps, and appropriately labeled diagrams to communicate scientific knowledge (e.g., motion of Earth’s plates and cell structure). e. Communicate the steps and results from an investigation in written reports and oral presentations.

Procedure:

1. Obtain/collect the various liquids of different colors to be used in tube to show the various layers.

In the demonstration I used the following:

1. honey,

2. baby oil.

3. vanilla syrup

4. liquid laundry detergent, and

5. liquid dishwashing detergent.

2. Next, I added the liquids to the long, clear, glass tube in a random order. I started with the baby oil, followed by the vanilla syrup. Honey came next and then laundry and dishwashing detergent. At this point, as the liquids were being deposited into the tube, it was quite clear that those with higher density or heaviness, immediately found their place in the bottom, the lighter liquids found their place on top. Key on the link to view photo:

http://picasaweb.google.com/117061658899343208804/Pictures

PHOTO

Final product of my demonstration in liquid density.

Student prior knowledge:

Students will already be knowledgeable about measuring the volumes

of different objects or materials. They will already have used various

measuring instruments such as rulers, cylinders, flasks, and beakers with differing units of measurements.

Explanation:

At this point, it is necessary to explain to students how the relative density of liquids will find their place in a test tube, with the heavier liquids moving to the bottom, while the lighter ones will move to the top of the tube. It is also extremely necessary to explain to students that they must exercise care in choosing the liquids in their demonstrations as some students may be inclined to experiment with flammables or toxic substances. They must be discouraged and not permitted to use flammables or liquids that may cause harm to themselves, to others, or to home/school property.

At this point the teacher can show the students different quantities of the same material and ask them if the units all have the same density. If most students agree that they do, ask them to explain why? (Density represents the mass of one cubic centimeter of a substance, a value that is always the same.) Students must be explained that the constant value of a substance’s density makes it a useful property for identifying and distinguishing substances.

Questions and answers:

1. Why do objects that have are of different size many times weight different?

This has to do with the principle we have just studied in this demonstration. It all has to do with its mass to volume ration. A rock or the same size as bottle cork will weight a lot more than the cork. Why? Because the rock has more mass and therefore weights a lot more. It all has to do with the atomic structure of the elements, molecules, and compounds that make it up.

2. Why is it extremely important that ice is less dense than water:

If ice was more dense than water, then that means that all the lakes, rivers and some oceans would freeze in the bottom and all life in them would perish; which in turn would make human life more burdensome, more difficult. It is such a great fact that ice forms on top of rivers and lakes and animal life can exist underneath. If the ice at the bottom of oceans froze pushing the water up, then the water that moves up most likely would also freeze creating a vicious cycle which would most likely destroy all forms of life, from the smallest microbes to the biggest mammals.

3. What are density currents?

Density currents take place where liquids of different densities meet, such as a river moving into an ocean. The saltwater is heavier than the freshwater without necessarily taking more space. However, if for example, fresh water is mixed with lots of mud, then it may become denser than seawater, thus creating another density current.

Applications to everyday life:

1. Moving liquids from point A to point B.

Engineers, business people, governments, and others need to be able how liquids behave in order to transport massive of amounts of a certain substance over long distances. This would influence preparation, costs, convenient routes, supplies, materials, manpower, risks, etcetera. Understanding the behavior of the corresponding liquids will greatly facilitate its transportation in all various aspects.

2. Many items in the grocery stores are packed by volume but sold by weight, so buying the bulkiest bag does not necessarily mean that we are getting the best deal in terms of economics.

3. Because the density of water increases with an increase in salinity or decrease in temperature, ships sailing from a cold area to a warm area will sink lower in the warmer area due to an due to the density change in the water.

Video: click on the following link:

http://www.youtube.com/watch?v=XzBgZ5JhWqs

References:

1. World wide web

2. Addison-Wesley Chemistry, 4^th Edition

3. Prentice Hall Science Explorer

4. The sourcebook for teaching science, Dr. Norman Herr,

California State University Northridge