The Density of Liquids and Solids

Description

Common liquids and solids of various densities are layered in a beaker. The liquids form different layers and the solids float at the interfaces between them. This demonstrates that a solid's ability to float or sink depends on its density relative to the liquid it is in.

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• Density is the ratio of the mass of a substance or object to its volume. At any given temperature, the ratio of mass to volume is characteristic for a given substance.
• Place the beaker containing the density gradient prepared according to the procedure in a prominent location in the classroom. After discussing the phenomenon, leave the display up for several days. This will allow the students to observe the effect that time has on the layers. Students are frequently curious about whether the layers will change position or mix over time.

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1. Measure 100 mL of each liquid into graduated cylinders. Add a few drops of food coloring to the water.
2. All liquids should be poured into the 600-mL beaker using a stirring rod to guide the liquid. Try to avoid mixing the liquids while pouring them into the beaker. The liquids and solids should be added to the 600-mL beaker in the following order:
   1. Pour the corn syrup (or concentrated salt solution) into the beaker. This is the most dense liquid layer. If a salt solution is used, color it with food coloring.
   2. Place the steel alloy sample gently into this layer. Place the pink pearl eraser on the layer.
   3. Add food coloring to the glycerol; mix. Pour in the glycerol slowly using a stirring rod.
   4. Place the gum eraser on the glycerol layer.
   5. Pour the colored water into the beaker and place the plastic sample on the water layer.
   6. Pour the corn oil into the beaker and place the wood sample on the corn oil layer.
3. Cover the beaker and allow it to stand overnight.
4. Observe carefully.

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Name ___________________________ Class ________

Teacher__________________________

DoChem 012 The Density of Liquids and Solids

1. Order the solid substances used in this demonstration by density. List the most dense substance first.
2. Order all substances used in this demonstration by density. (both solids and liquids)
3. How can this experiment be performed so that quantitative estimates of the densities of the liquids are made?
4. Describe an application where the density of substances is used for a separation.

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Purpose

• To show that materials of lower density float on liquids of higher density.
• To calculate the densities of various liquids.

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• 1 600-mL low form beaker, or similar container
• 100 mL corn syrup or concentrated salt solution
• 100 mL glycerol
• 100 mL tap water
• 100 mL corn oil
• food colorings
• 1 piece of wood (cork)
• 1 piece of plastic
• 1 piece of pink pearl eraser
• 1 piece of gum eraser
• 1 piece of steel alloy (washer, nut, etc.)
• 4 100-mL graduated cylinder
• 4 stirring rod

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• Saturated salt solutions may also be used. Consult a reference such as the Handbook of Chemistry and Physics (Chemical Rubber Publishing Company) for suggestions regarding solutions of high density.
• The solid samples should be small enough to fit into the 600-mL beaker.
• There is some mixing between the water and glycerol layers after several days.

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Teacher preparation: 50 minutes

Presentation Time: 15 minutes

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There are no unusual hazards in this experiment.

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No special precautions are required in this experiment. Follow routine laboratory precautions.

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After removing the solids, wash the liquids down the sink with hot soapy water. The solids may be cleaned and saved for future use.

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Presentation Question:

• How can this experiment be performed so that quantitative estimates of the densities of the liquids are made?
  • A series of calibrated floating objects (usually colored spheres) can be used. For example, if the spheres of density 1.12 g/mL and above sink while those of density 1.10 g/mL and below float, the density is somewhere in the range 1.10-1.12 g/mL.

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• Students may be aware that oil and vinegar salad dressing must be mixed before each use, because the two liquids separate according to their densities.
• The antifreeze content of an automobile radiator is determined by measuring density.
• Multilayered, gelatin-based desserts separate into layers on the basis of differences in density.

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1. Steel alloy (nut), pink pearl eraser, gum eraser, plastic, wood
2. Steel alloy (nut), Syrup, pink pearl eraser, glycerol, gum eraser, water, plastic, oil, wood
3. See Presentation question.
4. Many are answers possible. See Applications.

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• density
• layer
• multilayer

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