EXERCISE 22

Determination of Specific Heat and

The Atomic Weight of an Element

Objective:

To determine the specific heat of an element and to calculate the atomic weight of an unknown element using Dulong and Petit law.

Chemist in the early years of the development of chemistry used Dulong and Petit's law to determine the atomic weight of unknown elements. Dulong and Petit law states that the product of specific heat and atomic weight of an element is nearly a constant.

specific heat x atomic weight = 6.2

Equipment:

1. styrofoam cup

2. thermometer

3. beaker

4. balance

Procedure:

1. Weigh out a test tube to the nearest .01 g.

2. Obtain unknown sample from the stock room and place the sample in the test tube and weigh to nearest .01 g.

3. Weight of sample.

4. Place test tube and sample in boiling water for at least 15 minutes and record the temperature of the water to the nearest 0.1C.

5. Weigh 50 g of water in a styrofoam cup and record the temperature to the nearest .1C.

6. Now immediately transfer the metal to the styrofoam cup, making sure not to splash. Mix thoroughly and record the highest temperature of the mixture.

7. Assume no heat lost to the surrounding and to the cup. Calculate the specific heat of the element. Remember--heat lost by the element is equal to heat gained by the water.

heat lost = heat gained

(mass) (specific heat) (DT) = (mass) (specific heat) (DT)

 


EXERCISE 22 (continued)

8. From the value of the specific heat of the unknown element calculate its atomic weight.

9. Obtain the accepted specific heat from your instructor.

10. Calculate the percent error and show all your work.

 


EXERCISE 22

ANSWER SHEET

NAME SECTION

DATE SAMPLE NO.

1. weight of test tube __________________________________

2. weight of test tube and sample __________________________________

3. weight of sample __________________________________

 

 

4. temperature of sample

(in boiling water) __________________________________

 

 

5. weight of water __________________________________

6. temperature of cold water __________________________________

7. temperature of the mixture __________________________________

8. specific heat of the unknown __________________________________

9. atomic weight of the unknown __________________________________

10. accepted specific heat __________________________________

11. percent error __________________________________