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Calorimetry Lab

The purpose of this lab is to measure the specific heat capacity of an unknown metal. We don’t actually know the specific heat capacity of the metal, so our goal is not to get the “right” value. Rather, we’re focusing on the process of measurement and how to do calculations, as you’ll see below.

Materials: Hot plate, beaker, string, nut-and-bolt combination, electronic balance, Styrofoam cup, plastic soda-cup lid, thermometer.

Pre-Lab Question

The following question will help prepare you for the analysis portion of the lab. A piece of metal with a mass of 25 g and an initial Temperature of 95 ºC is dropped into 500 g of water with an initial Temperature of 25 ºC. After sitting for 10 minutes, the final Temperature of the water and metal together is measured to be 45 ºC. What is the specific heat capacity of the metal? (The specific heat capacity of water is 4.184 J/g ºC).

Lab Procedure

1. Fill a 250mL or larger beaker about ¾ full with water. Place it on a hot plate and allow the water to boil.

2. While waiting for the water to boil, measure the mass of one of the nut-and-bolt combos. Record the mass (mmetal) here:___________.

2. Measure the mass of a Styrofoam cup. Record the mass (mcup) here:_______________.

3. Fill the Styrofoam cup about halfway full with water. Record the mass of the cup-plus-water (mcup + water) here: ____________.

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4. Tie at least 12 inches of string around your metal nut and-bolt-combo. Drop the metal into the water, leaving the string hanging out so you can pull the metal out later. Place a soda cup lid on the cup, and place a thermometer through the hole on the lid and down into the water (this is your Calorimeter). After approximately 5 minutes, record the temperature (Ti) here: ___________.

5. Take the lid off the cup, and remove the metal using the string (NOTE: Don’t toss out the water—you’ll need the Calorimeter later on). Lower the metal into the beaker of boiling water (like before, leave the string hanging over the edge of the beaker, so you can pull it out later). CAUTION: Be careful to lower the metal slowly so as not to break the beaker. Leave the metal in the boiling water (100 ºC) for at least 5 minutes.

6. After about 5 minutes, use the string to pull the metal out of the boiling water. Drop it into the Calorimeter, and wait for the temperature to stop rising (3-5 min). Measure the final temperature (Tf) here: ______________.

Analysis

We’re going to use the equation Q = mC∆T to calculate the specific heat capacity of the metal.

Subtract: mcup and water – mcup = mwater: ___________g.

The specific heat capacity of water cwater = 4.184 J/gºC.

Since the metal and the water reach equilibrium in the Styrofoam cup,

Tf metal = Tf water = Tf =_________________ ºC (this is what you recorded in step 6 above).

Therefore, ΔTmetal = Tf –100 ºC = _________________.

And ΔTwater = Tf-Ti water = ___________ºC.

mmetal = ____________g.

The heat that transferred out of the metal = the heat that transferred into the water. In other words, -Qmetal = Qwater.

So use the equation—

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-(mmetalcmetal ΔTmetal) = mwatercwater ΔTwater

—to solve for cmetal.

Record cmetal: _____________ J/g ºC.

Questions

1. Assume the specific heat capacity of the metal is 0.40 J/g ºC. What is the percent error of the value you calculated? Remember the Equation for Percent Error: [Experimental Value – Accepted Value] *100%

(Accepted Value)

2. What are some possible sources of error in the experiment? (Think about the set-up)

3. What if you had used a greater mass of water in the calorimeter. Would you expect to have found a different value for cmetal? Explain.

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4. What if the specific heat capacity of water magically changed to a smaller number. Would you expect the final temperature Tfinal that you measured to be greater or smaller? Explain.