Determination of Specific Heat of a Metal

Experiment-6: Specific Heat of a Metal Specific Heat is defined as the amount of heat energy required to raise the temperature of 1.00 o

o

g substance by 1 C. Two popular units for specific heat are cal/g x C (cal g -1 oC-1) and J/g x o

C (J g -1 oC-1). Specific Heat of water is 1.00 cal g -1 oC-1 o

A calorie is amount of heat required to raise the temperature of 1.00 g of water by 1.00 C. 1 cal = 4.184 Joules 1000 cal = 1 kcal Heat energy is measured in calories or joules. The amount of heat absorbed/released depends upon the mass of sample, its specific heat, and the temperature difference. For example, calculate the amount of heat necessary to raise the temperature of 40.00 g of water from 22.0 o

o

C to 45.0 C:

Heat absorbed = mass of water x specific heat of water x T o

o

o

= 40.00 g x 1.00 cal/g x C x (45.0 C - 22.0 C) cal = 920 cal Metals are good conductor of heat. Therefore, metals have low specific heat values indicating the fact that metals need less heat to raise their temperatures. In this experiment, a coffee-cup is used as the ‘Insulated Calorimeter’. Therefore, the heat lost by the hot metal sample is equal to the heat gained by the cold tap water. Heat lost by the hot metal

=

Heat gained by Water

[Mass of metal sample x specific heat of the unknown metal x temperature drop] cal = [Mass of water x specific heat of water x temperature gain] cal All numbers are known from the experimental observations except specific heat of the unknown metal, which will be computed at the end.

Procedure: 1. Please put coffee cups and the metal samples back after you finish your experiment because these are reusable. Review Figure 1 and 2. 2. Fill up a 600 ml or 400 ml beaker 2/3rd with regular tap water. Put this beaker on top a hot plate. Put your unknown metal sample in a test-tube. The metal should fill-up approximately 1/3rd of the test-tube. Clamp this test-tube using a metal utility clamp to the Iron stand. Carefully suspend this test tube into the beaker containing water. The test tube should not touch the bottom of the beaker.

Now, turn on your hot plate. Bring the water to a boil. Let the

water boil for 10 minutes. While waiting you may do the following steps. 3. Obtain one coffee cup. Find its mass. Record all the digits. 4. Put 40 ml tap water into this coffee cup. Find the mass of coffee cup plus water. Now, place the coffee cup in an empty 400 ml beaker for support to avoid any spill. 5. Insert a thermometer into this water sample in the coffee cup. Hold it vertical for 3-4 minutes. Read and record the temperature of this cold-water sample. Take out this thermometer and insert into the boiling hot water. Read and record the temperature of boiling hot water. The temperature of the hot metal in the test tube is same as the temperature of boiling hot water. Put this thermometer aside. Do not shake the thermometer! Use only one thermometer throughout the experiment. 6. Carefully transfer, as demonstrated by your teacher, the hot metal into the coffee cup containing water. Swirl the contents (water + metal) for 15 seconds. Insert the thermometer into the (water + metal) mixture in the coffee cup. Hold it vertical for 3-4 minutes. Read and record the temperature. This is known as the Equilibrium temperature of the mixture. 7. Shut-off the hot plate. Unplug it. Carefully throw away the hot water in the sink. Drain out water from the coffee up. Save the metal and coffee cup for future use. 8. In this experiment, you have made three mass measurements and three temperature measurements.

Laboratory Report#6: Specific Heat of a Metal Last Name_____________________________, first name________________ Date of Experiment______________ Instructor’s Initials__________ 1. Mass of an empty Styrofoam cup

= …………………………….g

2. Mass of the Styrofoam cup with water

=…………………………….g

3. Mass of Water in the cup (#2 - #1)

=…………………………….g

4. Temperature of regular cold tap water, in the Styrofoam Cup

o

=…………. C (around 22.0 oC)

(Do not shake the thermometer!) o

5. Temp.of hot unknown metal sample = Temp. of boiling hot water =……. C (around 100.0 oC) (Do not touch bottom of the beaker!) 6. Equilibrium temperature (after pouring the hot metal sample into the Styrofoam Cup o

containing regular cold tap water) =……. C 7. Mass of the Styrofoam cup with regular cold tap water and Metal sample=………………….g =…………………………….g

8. Mass of the Metal sample (#7 - #2) 9. Heat gained by Water

= [mass of water x specific heat of water x temperature gain] cal o

o

= [# 3 g x 1.00 cal/g x C x (#6-#4) C] cal = #3 x (#6-#4) = …………………….. cal 10. Heat lost by the hot metal = Heat gained by Water = Same value as calculated in step-9 = …………………….. cal = [Mass of metal sample x specific heat of metal x temp. drop] cal = [# 8 g

o

x X cal/g x C

o

x (#5-#6) C] cal

11. Specific heat of metal, X = (Heat gained by Water) / (Mass of metal sample x temperature drop) o

= [(#9) / (#8 x (#5-#6)] cal/g x C o

=……………………………… cal/g x C

Show all your work and use proper units and significant figures! o

1. 50.00 g of a metal sample is heated to 100 C and then it was dropped into 85.0 g of water at o

o

22.0 C. The equilibrium temperature of the mixture was found to be 25.0 C. Calculate: (a) Heat gained by the water

(b) Heat lost by the metal

(c) Specific heat of the metal

2. Calculate the number of calories needed to increase the temperature of 50.0 g of copper metal o

o

o

from 21.0 C to 75.0 C. Given, the specific heat of copper is 0.382 cal/g x C.

3.

o

What will be the final temperature if 2000 g of copper at 95 C loses 10 kcal of heat?