101 Chemistry October 10, 2007
Unit 7 Density, Activity 7.2 - Outline for Lesson Plan
Activity 7.2 Comparing the density of objects to the density of water. Objectives: o Students should be able to predict which objects will float and which objects will sink o Students will learn how to compare the density of water to two or more other objects o Students will learn how to create a balance point on a standard ruler o Students see how to create a homemade balance using scotch tape, a standard pencil and a ruler o Students should be able to explain why the size of an object does not determine whether it will sink or float, for example they can compare a large piece of wood to a small pebble. Michigan Benchmarks and Standards: o Matter and Energy (PME) IV.1 Elementary Middle School High School All students will measure and describe the things around us: Describe and compare objects in terms of mass, volume, and density. Key concepts: Units of density--grams per cubic centimeter or grams per milliliter. Measurement tools: Balance, measuring cup or graduated cylinder, metric ruler. o See C-I.1 m.4 (making measurements) Real-world contexts: Common objects and substances. Explain when length, mass, weight, density, area,volume or temperature are appropriate to describe the properties of an object or substance. Key concepts: Appropriate metric (s.i.) units. o C-I.1 m.4 (use measuring devices) Measurement tools: Balances, spring scales, measuring cups or graduated cylinders, thermometers, metric ruler. Real-world contexts: Common substances such as those listed in PME-IV.1 e.1; hot and cold substances, such as ice, snow, cold water, hot water, steam, cold air, hot air.
Hypotheses: o If the water is heavier than the objects tested then the balance will be more weighted in favor of the side that holds the water container. o If clay is denser than water it will sink in the water. o If wax is less dense than water it will float in water. o Ice cubes are frozen water so they should be less dense than water For the independent variable I will use an empty tealight candle holder to hold objects with different densities to compare against the water. o Clay o Wax o Ice For my dependent variable I will use a volume of water exactly equal to the size of my tealight candle holder. The balance point on the ruler and the placement of the tealight candle holders on the balance will not change during this activity.
Required Materials Room-temperature water Tealight candles in metal containers Clay or play dough Wide, clear plastic cup Ruler Pencil Permanent marker & scotch tape
Quantity Needed ~ Cup Four Two small lumps One One One One each
Safety Rules for Children: o Pour water very slowly and carefully o Use care when working with permanent markers o Be careful when handling the metal tealight holders so as not to bend them o The candle holder filled with ice will be cold to the touch, handle it carefully In order to understand this mini lesson, students will need to have a basic understanding of density and comparison of objects to one another. They will also need an understanding of why the relative size of an object not does determine its density. Step-by-step Procedures: o For Comparing Water to Wax:
Construct a balance using a pencil and a ruler. The pencil should lie underneath the ruler and perpendicular to it so that the two objects form the shape of a cross. Mark a balance point on the ruler directly above the center of the pencil Remove the candles from the two tealight holders and set aside Tape one empty candle holder to each end of the ruler, being sure the holders line up exactly with the edge of the ruler Obtain a small amount of water in a beaker Carefully place the wax you removed back into one of the empty candle holders. Make a prediction about whether wax is heavier than water Carefully pour an amount of water exactly equal to the amount of wax you have into the other empty candle holder Note the difference and state your results Carefully drain the water from your candle holder Remove the two tea light candle holders from the balance
o For Comparing Water to Clay: Using the same balance and balance point from your wax experiment place two empty candle holders on the ends of the balance. Obtain a small amount of water in a beaker Obtain a chunk of clay or play dough large enough to completely fill one of your empty candle holders Make a prediction about whether clay is heavier than water Carefully press the clay into one of the empty candle holders so that it is completely full with a smooth top and replace it onto one end of the ruler Carefully and slowly pour an amount of water exactly equal to the amount of clay you have into the other empty candle holder Note the difference and state your results Carefully drain the water from your candle holder Remove the two tea light candle holders from the balance You may save your candle holder filled with clay for use in an additional experiment
o For Comparing Water to Ice: Using the same balance and balance point from your wax experiment place an empty candle holder on one end of the balance. Obtain a small amount of water in a beaker Obtain a tea light candle holder that has been previously filled with water and frozen overnight.
Place the ice-filled tea light candle holder on one end of the balance Make a prediction about whether ice is heavier than water Carefully and slowly pour an amount of water exactly equal to the amount of ice you have into the empty candle holder on the other end of the ruler Note the difference and state your results Carefully drain the water from your candle holder Remove the two tea light candle holders from the balance taking care with the ice filled holder so it doesn't melt onto the countertop.
Conclusion for comparing water to wax: o The wax was lighter than water and therefore the candle was able to float in our cup of water. My original hypothesis was correct. Conclusion for comparing water to clay: o The clay was heavier than the water and therefore sunk to the bottom of our cup of water. My original hypothesis was correct. Conclusion for comparing water to ice: o The ice was heavier than the water and therefore floated to the top of our cup of water. My original hypothesis was correct.