Do you think these two liquids have the same or different densities? Students should conclude that the liquids must have different densities. Explain that the cup with the floating candle contains water and the cup with the sinking candle contains isopropyl alcohol. Students should reason that the liquids must be different and have different densities. The candle will float on water and sink in alcohol.Īsk students: What might be causing one candle to float and the other to sink? Explain that the two candles are the same. Place a tea light candle in a cup with water and another tea light candle in a cup with alcohol.Demonstrate the density of two liquids with sinking and floating.Measure 50 mL of isopropyl alcohol and pour it into another identical clear plastic cup.Use a graduated cylinder to measure 50 mL of water and pour it into a clear plastic cup.Engage Do two demonstrations to show that different liquids have different densities.Students can use the smaller version of the same balance, Delta Education, Primary Balance (12-inch), Product #WW020-0452. One of the least expensive is Delta Education Primary Balance (21-inch) Product #WW020-0452 (21-inch). BalanceĪ simple balance is all that is required for the second demonstration. Although the isopropyl alcohol solution is 91% alcohol and 9% water, you can disregard the small amount of water for the purpose of this lesson. If that happens, do not do that demonstration. If you can’t find 91% solution, 70% will work, but your candle might not sink in it. The demonstrations and activity work best with 91% isopropyl alcohol solution, which is available in many grocery stores and pharmacies. Notes about the Materials Isopropyl alcohol Keep it away from any flames or spark sources. When using isopropyl alcohol, read and follow all warnings on the label. Make sure you and your students wear properly fitting goggles. The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan. Evaluationĭownload the student activity sheet, and distribute one per student when specified in the activity. Students will be able to determine whether a liquid will sink or float in water by comparing its density to the density of water.
They will predict the relative densities of the liquids and then measure their volume and mass to see if their calculations match their observations and predictions. Students will observe three household liquids stacked on each other and conclude that their densities must be different.
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