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# Comparing Density of Liquids & Solids Mark as Favorite (4 Favorites)

LAB in Observations, Density, Physical Properties, Matter, Kitchen Chemistry, Kitchen Chemistry - Middle School, Kitchen Chemistry - Elementary School. Last updated November 06, 2023.

### Summary

In this lab, students will use the water displacement method to measure the volume of small objects, measure their mass, and calculate their density. They will also calculate the density of different liquids and predict which objects will float or sink in which liquids.

Elementary and Middle School

### Objectives

By the end of this lab, students should be able to

• Measure mass and volume of liquids and solids.
• Calculate density.
• Compare density of liquids and solids.
• Understand how substances dissolved in a solution can affect the density of the solution and whether objects will sink/float in those solutions.

### Chemistry Topics

• Density
• Mass
• Volume of liquids and solids
• Measurement

### Time

Teacher Preparation: 15 minutes
Lesson
: 50 minutes

### Materials

Each group will need:

• 2- 250ml beakers
• ~300 ml tap water
• 1/4 cup salt (approx. 76 g of table salt)
• 4 or 5 small objects that can fit into the opening of a graduated cylinder. (Some options include a stone, a plastic, wood, or metal cube or irregularly shaped object, a piece of candle or crayon, an eraser, a cherry, grape, or other small fruit.
• Digital gram scale
• Paper towels for clean up

### Safety

• Always wear safety goggles when handling chemicals in the lab.
• Be careful with glass materials. Report any broken glass immediately to the teacher.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Students should wash their hands thoroughly before leaving the lab.

### Teacher Notes

For this activity to work well for students, the objects chosen must be small enough to fit into the opening of a graduated cylinder but large enough to displace enough water so students can discern the change in volume of water using the water displacement method.

Also, if you choose an object that floats in water, you will need to instruct students to use a pencil or their finger to push the object down just under the surface so that the pencil or finger barely touches the surface of the water.

• Background:
• Mass is the amount of matter in an object. It is measured in grams (g).
• Volume is the amount of space an object takes up.
• The volume of a liquid can be found using a beaker or graduated cylinder. It is measured in milliliters (ml).
• The volume of a solid can be found using the water displacement method in a graduated cylinder. The volume of a solid is measured in cubic centimeters (cm3). The water displacement method is convenient because 1 ml = 1 cm3.
• To use the water displacement method, add water to a graduated cylinder and note the original volume of the water. Then add the solid. Note the new volume. The new volume minus the original volume of water equals the volume of water displaced by the solid. This is also equal to the volume of the solid in cm3.
• Density is the amount of mass in a given volume of a substance.
• Density = mass / volume
• Density is a physical property of an object and can be used to identify substances.
• Objects which are more dense than water will sink in water; objects which are less dense than water will float in water.
• Saltwater solutions are more dense than water because salt water has more mass in the same volume of liquid.
• Have materials set up at lab tables when students arrive, including paper towels in case of spills.
• Ideal group size = 2-4 students
• Groups of 4 can designate a member for each object to determine its mass, volume, density, and if it sinks or floats in water and/or salt water.
• Classroom management tips:
• Elementary teachers may decide to have the mass of the beakers already labeled on the beakers and the water already poured into the beaker. To do this, place the beaker on the scale while it is empty. Write the mass of the beaker on a label on the beaker. Pour 100mL of water into each beaker and into the graduated cylinder.
• Mark a line with a dry erase marker on each beaker and graduated cylinder pointing to 100 mL mark so that students can easily identify how much water is in each.
• Students can sometimes forget that subtractions need to be made for volume of solids and mass of liquids inside the beaker. This can be remedied by setting up the subtraction problem for them on their lab report format or having a reminder taped next to the scale and graduated cylinder.
• Pre-portion ¼ cup of salt (76g) for each group in a small plastic cup or a separate beaker or graduated cylinder to save time having to do this additional measurement.
• Differentiation:
• Lower level students can have a lab report worksheet, which includes the measurements noted above and subtraction problem set up.
• Higher level students can make the additional measurements.
• Technology option: have students set up a lab report in PowerPoint with one step of the scientific method on each slide (Slide 1 = Purpose, Slide 2 = Research, Slide 3 = Hypothesis…)
• Early finishers can examine a liquid density column model with a list of substances in the column and their density (out of order). These students can identify which substance is which by putting the density in order from least to greatest, then labeling the substance with the least density at the top and the substance with the greatest density at the bottom.
• You can find a useful video animation on comparing Density on the AACT website.

### Background

Some physical properties of matter include mass, volume, and density. Mass is the amount of matter in an object, which is measured in grams
using a triple beam balance or electronic scale. Volume is the amount of space an object takes up. For liquids, volume is measured in milliliters (mL) using a beaker or graduated cylinder. For solids, it is measured in cubic centimeters (cm3). Once you have identified mass and volume, you can divide in order to find the density of a substance. Density equals mass divided by volume (D=m/v). Water has a density of 1 g/mL. If a substance is more dense than water, it will sink in water. If a substance is less dense than water, it will float.

### Prelab Questions

1. Do you think that saltwater will be more dense or less dense than tap water? Explain your thinking.
2. Which of the solids on the materials list do you think will sink in tap water?
3. Which of the solids on the materials list do you think will sink in salt water?
4. Why is it important to record the mass of the empty beaker before pouring water into it?

### Objective

You will investigate how the density of an object affects whether it sinks or floats in tap water and in saltwater.

### Materials (for each group)

• 2- 250ml beakers
• ~300 ml tap water
• 1/4 cup salt (approx. 76 g of table salt)
• Digital gram scale
• Calculator
• Paper towels

### Safety

• Always wear safety goggles when handling chemicals in the lab.
• Be careful with glass materials. Report any broken glass immediately to your teacher.
• Follow instructions to clean up materials and dispose of any chemicals.
• Wash your hands thoroughly before leaving the lab.

### Procedure

Mass and Volume of Liquid and Solution:

1. Place beaker 1 on the scale while it is empty. Record the mass of the empty beaker.
2. Repeat step 1 using beaker 2.
3. Pour 100 mL of water into each beaker.
4. Pour ¼ cup (76 grams) of salt into beaker 2 and stir until it seems completely dissolved.
5. Place beaker 1 with tap water on the scale. Record new mass.
6. Subtract to find the mass of the water: new mass minus the mass of the empty beaker.
7. Repeat steps 5-6 using beaker 2.
8. Record any change in volume of saltwater solution on your data table.

Density of Liquid and Solution:

1. Divide mass of the liquid in beaker 1 by its volume to determine its density. Record measurements and final answers in the “Calculations” data table.
2. Divide mass of the liquid in beaker 2 by its volume to determine its density. Record measurements and final answers in the “Calculations” data table.

Mass and Volume of Irregular Solids:

1. Place each object on the scale and record its mass in the data table.
2. Pour ~50 mL of water into the graduated cylinder. Record exact volume for “Volume of Water only” category in data table.
3. Place object 1 into graduated cylinder. Record new volume measurement in “Total Volume” category in data table.
4. Subtract “volume of water only” measurement from the “total volume” measurement to determine the volume of the solid.
5. Remove the object from the graduated cylinder and dry off.
6. Repeat steps 2-5 for each remaining solid.

Density of Irregular Solids:

1. Divide mass by volume for each solid to determine the density of each object. Record measurements and final density values in the “Calculations” data table.

Comparing Density:

1. Based on your density calculations, make predictions for each object about whether it will sink or float in tap water and in saltwater. Record your predictions in the data table below. Remember – objects with GREATER density than the liquid will sink, and objects with LESSER density than the liquid will float.
2. Place each solid in water, one at a time. Record if it sinks or floats.
3. Repeat step 2 with each solid in saltwater.

### Data

Mass and Volume of Liquid and Solution

 Substance Total Mass - Mass of Beaker = Mass of Substance Volume of Substance Tap Water Saltwater Solution

Mass and Volume of Solids

 Substance Mass Total Volume(object & water) - Volume of water only = Volume of Substance

### Calculations

Density of Liquids and Irregular Solids

 Substance Mass (divided by) Volume = Density Tap Water Saltwater

### Analysis

 Substance Tap Water Saltwater Solution Prediction Observation Prediction Observation
1. Which object had the greatest density in this lab activity?
2. Which object had the least density?
3. Did any object float in saltwater that did not float in tap water? If so, why do you think this happened?
4. Once you calculated the density of each object, were you able to accurately predict when the objects would sink or float in each liquid or solution? Why or why not?

### Conclusion

Refer back to the objective statement. Based on the results of your investigation, what did you learn about density and how it affects whether objects sink or float?

### Extension

Think about a helium-filled balloon floating in the air. What can you infer about the density of helium in the balloon compared to the density of the air surrounding the balloon?