HOT WASHER LAB

BACKGROUND

If you throw a hot rock into a pail of cool water, you know that the temperature of the rock will go down. You also know that the temperature of the water will go up—but will its rise be more than, less than, or the same as the temperature drop of the rock? Will the temperature of the water go up as much as the temperature of the rock goes down? Will the changes of temperature instead depend on how much rock and how much water are present and how much energy is needed to change the temperature of water and rock by the same amount?

You are going to study what happens to the temperature of water when hot or cold washers are added to it. Before doing this activity, think about the following questions.

1) Suppose that equal masses of water and iron are at the same temperature. Suppose you then add the same amount of heat to each of them. Would one change temperature more than the other?

YES NO

2) If you circled “yes,” which one would warm more?

WATER IRON

3) Again, suppose that equal masses of water and iron are the same temperature. Suppose you then take the same amount of heat away from each of them. Would one cool more than the other?

YES NO

4) If you circled “yes,” which one would cool more?

WATER IRON

PROCEDURE

STEP 1: Find the mass of 30 washers using the digital scale. Knowing what you know about density, figure out how much cold water you will need to equal the mass of the washers (hint, density of water is 1g/mL).

STEP 2: Pour the appropriate amount of ice-cold water into a 150mL beaker.

STEP 3: Place your washers into the “washer heating water” that the teacher has set up for you. Leave the washers in the water for at least 2 minutes to allow them to reach an equilibrium temperature.

5) Is the temperature of the hot water equal to the temperature of the washers? Why do you think it is or is not? Can you think of a better way to heat the washers to a known temperature?

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STEP 4: Just before you are ready to mix the washers with the ice-cold water, measure and record the temperature of the hot water around the washers.

Temperature of cold water = ________________°C

Temperature of hot water = ________________°C

STEP 5: Predict what the temperature of the mixture will be when the hot washers are added to the cold water.

Predicted temperature of mixture = ____________________°C

STEP 6: Lift the washers from the hot water and put them quickly into the cold water. Just before putting the washers in, start collecting data using Logger Pro.

STEP 7: When it is clear that the temperature on the graph has leveled off, record the value of that final temperature.

Actual temperature of mixture = ______________________°C

6) How close is your prediction to the observed value?

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STEP 8: Now you will repeat steps 1 through 7 for hot water and cold washers.

STEP 9: Put the washers in the ice-cold water and leave them in the hot water for at least 2 minutes (why?), and record the temperature of the water around the washers.

Temperature of cold water = _______________________ °C

STEP 10: Fill up the 150mL beaker with enough hot water to equal the mass of the washers (how do you know this mass?).

Temperature of hot water = _______________________ °C

STEP 11: Predict what the temperature of the mixture will be when the cold washers are added to the hot water.

Predicted temperature of the mixture = ______________________°C

STEP 12: Lift the washers from the cold water and put them quickly into the hot water. Just before putting the washers in, start collecting data using Logger Pro.

STEP 13: When it is clear that the temperature on the graph has leveled off, record the value of that final temperature.

Actual temperature of mixture = ______________________°C

7) How close is your prediction to the observed value?

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ANAYLSIS

8) Discuss your observations with the rest of your team, and write an explanation for what happened.

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9) Suppose that you have equal masses of water and washers at the same temperature. Suppose you then light similar candles and place a candle under each of the masses, letting the candles burn for equal times. Would one of the materials change temperature more than the other?

YES NO

10) If you circled “yes,” which one would reach a higher temperature?

WATER WASHERS

11) Suppose you have cold feet when you go to bed, and you want something to warm your feet. Would you prefer to have a hot-water bottle filled with hot water, or one filled with an equal mass of washers at the same temperature as the water? Explain.

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12) Why does the climate of a mid-ocean island stay nearly constant, getting neither very hot nor very cold?

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