The American Chemical Society is dedicated to improving lives through Chemistry. Skip Navigation. Lesson 3. Engage Do two demonstrations to show that different liquids have different densities.
Measure 50 mL of isopropyl alcohol and pour it into another identical clear plastic cup. Procedure Demonstrate the density of two liquids with sinking and floating Place a tea light candle in a cup with water and another tea light candle in a cup with alcohol. Hold up the two cups. Expected results The candle will float on water and sink in alcohol. Ask students: What might be causing one candle to float and the other to sink? Explain that the two candles are the same.
Students should reason that the liquids must be different and have different densities. Explain that the cup with the floating candle contains water and the cup with the sinking candle contains isopropyl alcohol. Do you think these two liquids have the same or different densities? Students should conclude that the liquids must have different densities. They may even realize that water is more dense and alcohol is less dense than the wax candle.
Procedure Demonstrate the density of two liquids by comparing the mass of equal volumes. Remove the candles from each liquid and tell students that each cup contains the same volume of liquid. Carefully place the cups of water and alcohol on opposite ends of a balance. Expected results The water will weigh more than the alcohol.
Ask students: Which liquid is more dense? Students should agree that the water is more dense than the alcohol. How do you know? Since the water has more mass than an equal volume of alcohol, water must be more dense.
Explore Demonstrate that liquids can float or sink in other liquids by making a density column with water, oil, and alcohol. Procedure Pour about 15 mL of water into the graduated cylinder.
Show students the layered liquids in the graduated cylinder and point out that the alcohol floats on the oil while the water sinks. Expected results Alcohol floats on oil and water sinks in oil.
Ask students: Why does the alcohol float on the oil? They should conclude that the alcohol floats because it is less dense than the oil. Why does the water sink in the oil? Water sinks because it is more dense than oil. Explain that, just like solids, liquids are made from atoms and molecules, which have a certain mass and size. Depending on the mass of the molecules that make up a liquid and how closely they pack together, liquids have their own densities.
In the activity, you will compare the mass of equal volumes of each liquid. Which liquid do you think will have the most mass? The least mass? In between? Students should predict that the water will weigh the most, the alcohol will weigh the least, and the vegetable oil will weigh somewhere in between.
Give each student an activity sheet. Calculate the density of water, alcohol, and oil. This is because oil is less dense than water and therefore it floats to the surface. These beads, however, did not mix with the water. The detergent molecules can form bonds with both water and oil molecules.
This activity brought to you in partnership with Science Buddies. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Materials 2 clear plastic water bottles with lids 2 cups of water One-half cup of oil olive, cooking or vegetable oils will all work Liquid dishwashing soap Clock or timer Permanent marker Measuring cup Measuring spoon Food coloring optional Preparation Remove any labels from your water bottles.
Pour one cup of water into each bottle. Allow the bottle to sit on a countertop or flat surface while you observe the water and oil. Does the oil sink to the bottom of the bottle, sit on top of the water or mix with it? Does the oil sink to the bottom, sit on top of the water or mix with it? Try not to shake the bottle as you add the dish soap. Make sure the bottle caps are screwed on tightly to each bottle. Holding a bottle in each hand, vigorously shake the bottles for 20 seconds. Set the bottles down on a flat surface with plenty of light.
Although Phan and his team do not currently have support from any private organisations, they are looking for sponsors with hopes to work in the field some time soon. Source: Curtin University and ScienceDaily. Tags: nature , News , science , technology. You may also like… Plastic and print power Robot learns to recognise itself in a mirror Colour-changing robot inspired by octopus Climbing in the rain.
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