# Liquid Density - Hot and Cold

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## Objective

Students will be able to build a density column using hot and cold water in order to gain experience working with fluids of varying density.

#### Big Idea

Relationship with density are explored while constructing a density column with hot and cold water.

## NGSS Background

This lesson is based on California's Middle School Integrated Model of NGSS.

MS-PS1: Matter and Its Interactions

PE: MS-PS1-2 - Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. This lesson is specifically designed to assess the property of density within a substance.

DCI: PS1.A: Structure and Properties of Matter - Each pure substance has characteristic physical and chemical properties. Density is a property of matter that can be used to identify it.

SP4: Analyzing and Interpreting Data - Students will make predictions about the possible densities of hot and cold water before the actually build a density column. The students will later analyze their predictions and compare them to actual results.

CCC: Patterns - Macroscopic patterns are related to the nature of microscopic and atomic-level structure. Intrinsic particle movement, often described as temperature, causes water to achieve different levels of density. The students will be able to recognize that these different densities form a predictable patten in nature and can be used to identify specific types of matter.

The purpose of this lab is to give students hands-on experience with density and see for themselves that denser substance will displace less dense substances and sink to the bottom of a graduated cylinder. Buoyancy can be different for objects placed in the same material (water) with varying levels of density (hot vs. cold water).

This lab is often run as part of two other labs:

## Prelab (Set-up)

25 minutes

Materials

1. Empty baby food jar
2. Small beaker
3. Blue food coloring
4. Red food coloring
5. Ice
7. Pipet
8. Spoon

Student Directions

1. Fill half full the empty baby food jar with water. Place in the microwave for 30 seconds. Add several drops of red food coloring.
2. Fill the small beaker half full with water. Add a few ice cubes. Add several drops of blue food coloring and stir with the spoon.
3. Pour the cold water (blue) into the graduated cylinder, no more than half full.
4. Use the pipet to slowly add the hot (red) water a drop at a time and watch what happens. This may take a little practice – if you add the hot (red) water too fast you will force the colors to mix. Hold the pipet near the surface of the water and keep trying until you get it.
5. Repeat this same experiment, but pour the hot (red) water in first. Pipet the cold (blue) water one drop at a time.

TIP: The secret to build a clear density column is patience. The drops must be added very slowly and carefully. Any disturbance to the graduated cylinder will result is mixing of the food coloring and will spoil the effect of the density column.

## Lab (Student Activity)

15 minutes

Pass out Liquid Density Lab - Hot and Cold to each student.

Once the students have constructed their density columns they must show their columns to me. I spend a few minutes talking to the group of why their columns were or were not successful.

After I have approved their work they spend a few minutes answering questions before they clean up the equipment.

Review Questions

1. Does temperature change the density of water?
2. Prediction: (what do you think will happen).
3. Was your prediction right? Explain.
4. What happened to the colored water? Explain.
5. Did the water stay in layers? Explain.

Student Work Sample

## Extension

45 minutes

I created two Powerpoints that teaches density and buoyancy.

Density is mass per unit volume

The buoyant force acts on objects