Key Concepts

Since density is a characteristic residential property of a substance, every liquid has its own characteristic density.The thickness of a liquid determines even if it is it will float top top or sink in an additional liquid. A liquid will certainly float if it is less thick than the fluid it is placed in.A liquid will sink if it is much more dense than the liquid it is inserted in.

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Students will observe three family members liquids stacked on each other and also conclude that their densities need to be different. They will predict the family member densities that the liquids and then measure your volume and mass to view if their calculations match their observations and also predictions.


Students will be able to determine even if it is a liquid will certainly sink or float in water by to compare its thickness to the density of water.


Download the student task sheet, and distribute one per student when specified in the activity. The activity sheet will certainly serve together the “Evaluate” component of every 5-E great plan.


Make sure you and also your college student wear properly fitting goggles. Once using isopropyl alcohol, read and follow all warnings on the label. Isopropyl alcohol is flammable. Save it far from any kind of flames or spark sources.

Materials for Each Group

BalanceIsopropyl alcohol, 70% or higherWaterGraduated cylinder2 identical tall clean plastic cups2 tea light candles

Materials because that the Demonstration

BalanceIsopropyl alcohol, 70% or higherWaterGraduated cylinder2 similar tall clear plastic cups2 tea light candles

Notes around the Materials

Isopropyl alcohol

The demonstrations and activity work best with 91% isopropil alcohol solution, i beg your pardon is obtainable in numerous grocery stores and pharmacies. If friend can’t uncover 91% solution, 70% will work, however your candle can not sink in it. If that happens, perform not carry out that demonstration. Back the isopropil alcohol systems is 91% alcohol and 9% water, you deserve to disregard the little amount that water for the function of this lesson.


A straightforward balance is all the is required for the 2nd demonstration. Among the least expensive is Delta education Primary Balance (21-inch) Product #WW020-0452 (21-inch). Students deserve to use the smaller sized version the the very same balance, Delta Education, main Balance (12-inch), Product #WW020-0452.


Do 2 demonstrations to display that different liquids have various densities.


BalanceIsopropyl alcohol, 70% or higher WaterGraduated cylinder2 similar tall clean plastic cups2 tea irradiate candles

Teacher preparation

Use a i graduated cylinder to measure 50 mL of water and also pour it into a clear plastic cup. Measure 50 mL of isopropyl alcohol and also pour that into another identical clean plastic cup.


Demonstrate the thickness of two liquids through sinking and floatingPlace a tea irradiate candle in a cup v water and also another tea irradiate candle in a cup v alcohol. Hold up the 2 cups.

Expected results

The candle will float top top water and sink in alcohol.


Ask students:

What might be leading to one candle come float and also the various other to sink? describe that the 2 candles space the same. Students must reason the the liquids need to be different and have different densities. Describe that the cup v the floating candle includes water and also the cup through the sinking candle includes isopropyl alcohol.Do girlfriend think these two liquids have the same or various densities?Students should conclude the the liquids must have different densities. Lock may also realize that water is an ext dense and also alcohol is less dense than the wax candle.


Demonstrate the thickness of two liquids by comparing the fixed of same volumes.Remove the candle from every liquid and tell students the each cup includes the exact same volume the liquid.

Carefully location the cups of water and alcohol on opposite ends of a balance.


Expected results

The water will certainly weigh more than the alcohol.

Ask students:

Which liquid is an ext dense?Students have to agree the the water is more dense than the alcohol.How perform you know? since the water has an ext mass than an same volume of alcohol, water have to be much more dense. Explore

Demonstrate that liquids can float or sink in other liquids by make a thickness column v water, oil, and alcohol.

Materials because that the demonstration

Graduated cylinderWaterVegetable oilIsopropyl alcohol, 70% or greater

Note: If girlfriend would prefer the liquids come be more visible, add 1 autumn of food coloring to the water and also another drop of a different shade to the alcohol.


Pour about 15 mL the water right into the graduated cylinder. Slowly add around 15 mL of oil. Then gradually pour about 15 mL that alcohol top top top. The liquids should kind layers in the i graduated cylinder.


Calculate the density of water, alcohol, and oil.

Question come investigate

Why go water sink in oil and alcohol rise in oil?

Materials for each group

WaterVegetable oilIsopropyl alcohol (70% or higher)Graduated cylinderBalance that actions in grams

This task is created for students to make actual dimensions of the mass and also volume and to calculation the thickness of every liquid. Emphasize to students the they must be certain to accurately measure up the volume and mass of each liquid.


Find the fixed of an empty graduated cylinder. Document the mass in grams in the chart on the activity sheet.Pour 20 mL the water right into the i graduated cylinder. Try to be as precise as feasible by checking that the meniscus is right at the 20 mL mark. Weigh the i graduated cylinder with the water in it. Record the mass in grams. Uncover the fixed of only the water by subtracting the mass of the empty i graduated cylinder. Record the mass of 20 mL of water in the chart. Usage the mass and also volume that the water to calculation density. Document the density in g/cm3 in the chart.Follow procedures 2–5 because that alcohol and also then oil. Be certain to measure the oil last because it does not rinse conveniently from the i graduated cylinder. Table 1. Volume, mass, and also density for water, alcohol, and oil WaterAlcoholOilMass of graduated cylinder + liquid (g)Mass that empty graduated cylinder (g)Mass of fluid (g)Density of liquid (g/cm3)

Discuss even if it is the calculate densities assistance the order the liquids layer in the i graduated cylinder.

Ask students:

Do the densities girlfriend calculated explain why liquids float and sink in one another? Explain.Yes, the water is the many dense and also sinks in the oil. The alcohol is the least dense and also floats on the oil.Extend

As a demonstration, change the density of water so the a sinking carrot slice floats.

You may choose to do the adhering to either as a show or as an activity that students deserve to do.


Tall clear plastic cupWaterCarrot slice around ¼ inch thickSaltSpoon


Pour water right into a clear high plastic cup till it is around ½-filled. Ar a slice of carrot in the water.

Ask students:

Is the carrot much more or less thick than the water?Since the carrot sinks, students must conclude that the carrot is more dense than water.

Add around 1 teaspoon of salt come the water and also stir. Proceed to stir until the carrot floats to the surface ar of the salt water. If the carrot does not float to the surface, add an ext salt and also stir.


Expected results

The part of carrot must float in the saltwater.

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Ask student:

Is it much more or less dense than saltwater? because the carrot floats in saltwater, students need to conclude that the carrot is less dense than saltwater.How does including salt readjust the thickness of the water?Dissolving salt in water increases both the mass and also volume of the water, but it boosts the fixed more. Since D = m/v, enhancing the mass much more than the volume outcomes in boost in density.What would you intend if you placed equal quantities of water and also saltwater top top opposite ends of a balance?If equal quantities of water and saltwater were put on a balance, the saltwater would be heavier.