Exploring Heat and Temperature

Transcription

1 Exploring Heat and Temperature Molecular Motion and Heat In 1827, the botanist Robert Brown, looking through a microscope at particles found in pollen grains in water, noted that the particles moved through the water but was not able to determine the mechanisms that caused this motion. Many decades later, Albert Einstein published a paper in 1905 that explained in precise detail how the motion that Brown had observed was a result of the pollen being moved by individual water molecules. His paper also addressed how the addition of heat energy would increase the movement of the water molecules. Random Molecular Movement 1. Demonstrating Random Molecular Movement a. Materials: 2 petri dishes with water, lamp, pepper b. Place one of the petri dishes under the lamp, leave the second dish out of the light, and allow the water in the dishes to settle for one minute. Turn on the lamp. After two minutes compare the movement of the pepper flakes in the petri dishes. Record your observations in the space below.

2 2. Demonstrating Random Molecular Movement, Again a. Materials: Test Tube Rack, 3 test tubes, hot water, cold water, roomtemperature water, dropper, food coloring b. Fill each test tube half way with a different temperature water. Quickly add a drop of food coloring to each test tube. Record your observations each minute for four minutes in the space below. You may write or sketch your observations. Minute 1 Minute 2 Minute 3 Minute 4 3. Diffusion and Osmosis In 7 th grade life science you may have learned about diffusion and osmosis. If you didn t, you definitely will next year in 10 th grade biology. Diffusion is the movement of material from and area of high concentration to an area of low concentration, as a result of random molecular movement. Osmosis is the diffusion of water. So in your cells, pure water will move toward an area of less pure water (think salty water). In this activity, you will observe how osmosis and diffusion work and apply that to the produce aisle in the grocery store.

3 a. Materials: Hot and Cold Salt Water, 4 petri dishes, Hot and Cold Freshwater, Potato Slices, Balance b. Record the initial mass of four potato slices in the table below. Place one slice of potato in each salt water and one in each freshwater. Allow the potato slices to soak for 5 minutes. Pat the potatoes dry and record their final mass. Calculate the % change using the following formula: % Change = (Final Mass Initial Mass) X 100 (Initial Mass) Water Hot Salt Cold Salt Hot Fresh Cold Fresh Potato Slice Initial Mass Potato Slice Final Mass Potato Slice % Change 4. Wrapping Up Heat and Molecular Movement Use what you have used to answer the following questions: a. Explain how the addition of heat affects molecular movement. b. Use molecular movement to explain the difference between solid, liquid, and gaseous water c. Grocers spray a fine mist of water over their produce to encourage osmosis and make the food look fresher and healthier. Do you think they should use warm water or cold water? Explain your answer.

4 Expansion Effects of Heat 1. Expansion of Solids a. Materials: Wire Hanger, Hot Plate, Metric Ruler b. Bend the hanger so it is roughly square with a small opening left between the two ends. Record the separation in millimeters (mm) in the table below. Place the hanger on the hot plate (setting medium) and allow it to heat up, measuring the separation every minute for five minutes. c. BE CAREFUL DON T BURN YOURSELVES and DON T MELT THE RULERS!!!! Time Initial 1 Minute 2Minutes 3 Minutes 4 Minutes 5 Minutes Separation (mm) 2. Expansion of Liquids a. Materials: Stoppered Test Tube with Freshwater and Tube, Stoppered Test Tube with Alcohol and Tube, Stoppered Test Tube with Salt Water, Hot Plate, Beaker half full of water b. Place the three test tubes in the hot water bath and measure the height of the liquid above the top of the test tube. Record your results in the table below. Set the hot plate on high and remeasure the height of the liquids every two minutes for ten minutes. Record all results. c. BE CAREFUL DON T BURN YOURSELVES!!!! Time Initial 2 Minutes 4Minutes 6 Minutes 8 Minutes 10 Minutes Height (mm)

5 3. Expansion of Gases a. Materials: wet soda bottle, dry soda bottle, wet glass bottles, dry glass bottle, Hot Plate, Water Bath, 2 balloons b. Add a few drops of water to the bottles marked wet. Do not add any water to the bottles marked dry. Stretch a balloon over each glass bottle mouth and place the bottles in the water bath. Gently squeeze some air out of the soda bottles and screw the caps on. Place the bottles in the water bath. Record your observations of each balloon in the table below. Turn the hot plate on to high and record your observations of the balloon every minute for five minutes. c. BE CAREFUL DON T BURN YOURSELVES!!!! Bottle Initial Wet Soda Bottle Dry Soda Bottle Wet Glass Bottle Dry Glass Bottle 1 Minute 2 Minute 3 Minute 4 Minute Expansion of Gases Balloon on a Bottle 5 Minute

6 Heat vs, Temperature 1. Defining Heat and Temperature Read the article The Prepared Practitioner: Understanding Heat and Temperature. In the space below, draw a Venn Diagram that compares heat and temperature.

7 2. Estimating Temperature by Touch a. Materials: Egg Carton of Sample Materials, Thermometer b. Organize the 12 items in your egg carton from warmest to coldest. Record your results in the space below. Then take the temperature of the air and record that in the space below. Object Temperature Rank (1 is warmest, 12 is coldest) Object Temperature Rank (1 is warmest, 12 is coldest) Air Temperature 3. Measuring Temperature a. Materials: Reading How Does A Thermometer Work, Worksheet Temperature Conversion b. Read How Does A Thermometer Work. Write a 5 sentence summary of the article. Then complete the worksheet Temperature Conversion.

8 4. Calculating Calories By burning pieces of food, the chemical energy stored in molecular bonds is released as heat and light. The heat can be measured in units called calories. A calorie is the amount of heat (energy) required to increase the temperature of one gram of water by one degree C. A Calorie in food is actually 1,000 calories. So a tic tac (the one-calorie mint) could raise the temperature of one (1 ml) milliliter of water 1000 degrees Celsius if it was burned and all the energy was captured. Alternately, that same tic tac could raise the temperature of a liter of water by one degree Celsius. The more calories a food contains, the more heat is given off when burned. Foods high in calories will release large amounts of energy. One gram of a protein will release far fewer calories than one gram of fat. a. Materials: Corn Chip, Lighter, Beaker, Water, Thermometer, Ring Stand, Tongs b. Add approximately 20 ml of water to the beaker and record the temperature of the water. Place the beaker on the prepared ring stand. Hold the corn chip in the tongs provided. Using the lighter, set the corn chip on fire and IMMEDIATELY place the corn chip under the beaker. When the corn chip becomes difficult to hold blow out the flame. Record the temperature of the water. Use your data to complete the following equation and calculate the number of calories in the corn chip. The specific heat of water is 1 kilocalorie/kg deg.c.

9 Melting Ice: Investigating Heat Transfer 1. Exploring Conduction a. Materials: Metal Samples, Hot Plate, Candle Wax b. Set the various sample pieces on the hot plate. Add a small piece of wax on top of each sample. Turn the hot plate to medium and observe. Record how long it takes for the wax to melt on each sample. Sample Time to Melt 2. Exploring Convection a. Materials: Beaker, Hot Water, Colored Ice Chips b. Into the hot water, drop a few chips colored ice. Watch how the ice chips rise and fall as they melt and change temperature. Record your observations in the space below. 3. Exploring Radiation a. Materials: Lamp, Thermometer b. Set the thermometer on the table. Record the initial temperature. Point the lamp at the table and let the thermometer heat up for one minute. Record the final temperature. c. In the space below, describe what kind of energy transfer caused the thermometer to heat up, being sure to address the facts that convection causes heat to rise and air is a poor conductor of heat.

10 4. Investigating Conduction, Convection, and Radiation a. Materials: Ice, Ring Stand, Yarn, Lamp, Towel, Stopwatch b. In your own words, define the following terms: i. Conduction ii. Convection iii. Radiation c. In the space below, predict which scenario will cause the ice to melt the fastest. Then test your predictions and record the results. Scenario Hanging Ice Cube Ice Cube on Table Ice Cube on Counter Covered by Towel Ice Cube on Counter Under Lamp Prediction (1 is fastest, 4 is slowest) Time to Melt Type/s of Heat Transfer Involved