Density of common liquids

Each lab team will determine the density of water and one of the sample liquids. The class will then compile their information.

A lesson plan for grade 8 Mathematics and Science

By Sansia Coble

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Learning outcomes

Students will:

1. Demonstrate ability to measure accurately.
2. Demonstrate ability to collect and record data.
3. Demonstrate ability to use data in a formula to solve for density in ^g/_cm³;.
4. Correlate math skills, use of calculator, and ordering decimals.
5. Write up lab report by scientific method.
6. Find out the density of water and compare with common household liquids.
7. Find out that there is a relationship between the volume and mass of the volume in solving for density.

Teacher planning

Time required for lesson

2.5 hours

Materials/resources

• triple-beam balance
• graduated cylinder
• dropper pipette
• waste collection jar
• water
• six or more common liquids such as glycerin, pink shampoo, green alcohol, brown vinegar, cola, milk, vegetable oil
• data sheet
• lab instructions
• calculator
• one liter graduated cylinder or large clear container

Pre-activities

• Students should have practiced using the formula to find density. They could have already found the volume and density of an irregular object (rock, nail, coin, etc.)
• Students should have had instruction or practice in writing up a lab report by scientific method model.
• Students will observe the liquids to be tested and make a hypothesis as to the order of densities, from least dense to the most dense, recording this information.

Activities

1. Weigh a dry one hundred milliliter graduated cylinder on the triple beam balance, record.
2. Measure fifty milliliters of water (using dropper pipette to be accurate) in the graduate and weigh on the triple-beam balance. Record.
3. Subtract the mass in grams of the graduate from the total grams of #2 and record this value as the mass of the fifty milliliters (V) of water.
4. Using the mass of fifty milliliters of water, calculate the density, D=^M/_V or ^g/_cm³, of the water to the nearest tenth of a gram. The density of water should be 1.0. This should alert the students as to their accuracy of measuring. If they are not close to this value, repeat the procedure.
5. Using a dry graduated cylinder, weigh it to the nearest tenth of a gram. Record.
6. In this graduate, measure fifty milliliters(V) of the sample liquid given to you by your teacher. Be careful with the liquid clinging to the sides and use the pipette if necessary. Weigh and record the mass in grams to the nearest tenth. Record.
7. Subtract the mass in grams of the graduated cylinder from the total as you have done before and record the value as the mass in grams of fifty milliliters(V) of the liquid.
8. Calculate the density of the liquid by using the formula. Repeat the procedure two more times, and take an average.
9. Report the density of the liquid to your teacher, or enter it on the class table for the class to see and compare.
10. Observing the densities of the various common liquids from the class list, make a list of the liquids from least dense to most dense and compare with your hypothesis.
11. Make sure that each team pours the liquid they have tested into the clear thousand milliliter graduated cylinder to observe layering later.

Assessment

During the lab, the teacher will observe skills of students in using triple-beam balance and measuring volume. Ask questions about their data:

1. Why do you need to weigh a DRY graduated cylinder?
2. Why do you need to subtract the mass of the graduated cylinder?
3. What values are you using in the formula for density? If they use a different volume to weigh, will the liquid have the same density?

Assess the recorded data and calculations and the student’s Lab Report with hypothesis, data, comparisons, tables, and conclusion.

Supplemental information

Comments

Great lab for observing skills, discovering the concept of density, recording data, keeping up with different sets of data, the need for repeating the procedure and averaging, and giving them practice on writing up a lab report. This lab can be modified for different levels of skills by requiring only sections at a time. The students are fascinated at the layering of the liquids, especially if you can get a combination that layers well visually.