Heat Effects and Calorimetry Lab Report PDF

Preview

Summary

Heat Effects and Calorimetry Lab Report...

Description

Name: Akzhan Yestoreyeva

Date Performed: 26.02.2022

Experiment No. 5 Title of Experiment: Heat Effects and Calorimetry I. INTRODUCTION Heat is a form of energy, which can flow between objects. Two objects in contact, after a particular amount of time, can reach the same (equilibrium) temperature. Flow of the heat can be measured with a calorimeter, which is a container with insulating walls. The walls of the calorimeter eliminates heat flow from or to the surroundings. Heat required for a particular temperature change of a substance can be calculated using the following formula: q = (specific heat / S.H.)×m×∆t (1) where m is the mass of a substance, ∆t is the change in the temperature. The specific heat indicates the amount of energy needed for increasing the 1 gram substance’s temperature by 1°C. Hence, heat is measured in either calories or joules. The specific heat of water is 4.18 joules/g °C. The specific heat of a metal can be calculated when a weighed metal is placed in calorimeter with water. The change in temperature occurs as heat passes from metal to water. Heat absorbed by water is equal to the amount of heat that flows from metal to water. The two amounts of heat are equal in magnitude but opposite in direction, and can be represented by the following equations: qH2O = - qmetal (2) qH2O = S.H. H2O×mH2O×∆tH2O = - S.H. M×mM×∆tM (3) The molar mass of a metal is related to the specific heat as follows: Molar Mass = 25/S.H. (joules/g °C) (4) The enthalpy change for the reaction in aqueous solution, is equal in magnitude to the heat gained by water, which is equal in magnitude to the heat flow between the reaction mixture and the solvent, water. It can be represented by the equation q reaction = ∆H reaction = -qH2O (5) If the temperature of the water increases during the reaction, heat has been given off by the reaction mixture, and the reaction is exothermic; qH2O is positive, ∆H is negative, and vice versa for an endothermic reaction. When a solid is dissolved in water, the heat flow occurs. The heat effect of this reaction is called the enthalpy change of solution, ∆H solution: (6) NaOH(s)→Na+(aq)+OH-(aq); ∆H = ∆H solution When an acid and a base react, the neutralization reaction takes place. The heat effects of the neutralization reaction can be calculated by the formula: (7) H+(aq)+OH-(aq)→H2O ∆H = ∆H neutralization The objectives of the experiment are to determine specific heat values and molar masses of four different metals, calculate the heat of solution and neutralization of two reactions. The importance of the experiment is to learn how to implement the theoretical knowledge about the heat effect of different reactions in performing the experiment.

PROCEDURE Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

1

A. Finding the Specific Heat A 400-cm3 beaker was filled with water and heated to boiling. The sample of unknown metal in the test tube was weighed and placed into the beaker with hot water. The mixture was heated until the boiling. The temperature of the 40 cm3 water poured into the calorimeter was recorded, and the metal from the test tube was placed into the calorimeter. The mixture was stirred thoroughly. The minimum temperature of the water was recorded. The metal was dried, and the procedure was repeated with 50 cm3 of water and other samples of three different metals. B. Finding the Heat of Solution The calorimeter with 50 cm3 of water was weighed, and the temperature of the water was recorded. 5 g of a solid was placed into the calorimeter. After stirring the mixture and making sure a solid completely dissolved, the maximum or minimum temperature of the solution is recorded. The procedure was repeated with other solids. C. Finding the Heat of Neutralization The temperature of 25.0 cm3 of 2.00 M HCl and 25.0 cm3 of 2.00 M NaOH were recorded. The two solutions were placed into the calorimeter, and the maximum temperature reached by a neutralized solution was recorded. The value of 1.02 g/mL was used as an average density for all solutions and 4.18 joules/g °C as the specific heat of the water during the calculations. II. RESULTS, DISCUSSIONS AND CONCLUSIONS A. Specific Heat: A Trial 1

B

E

H

Trial 2

Trial 1

Trial 2

Trial 1

Trial 2

Trial 1

Trial 2

1.

Mass of 72.26 stropped test tube plus metal, g

72.26

88.9

88.9

87.62

87.62

85.41

85.41

2

Mass of test tube and stopper, g

43.02

43.02

43.04

43.04

43.04

43.23

43.23

42.78

3

Mass of calorimeter, g

282.18

282.18

282.18

282.18

282.18 282.18 282.18

282.18

4

Mass of calorimeter and water, g

321.34

331.7

322.43

332.36

322.2

332.25 322.2

332.23

5

Mass of water, g

39.16

49.52

40.25

50.18

40.02

50.07

40.02

50.05

6

Mass of metal, g

29.24

29.24

45.86

45.86

44.58

44.39

42.18

42.63

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

2

7

20.2 Initial Temperature of water in calorimeter, °C

20.9

20.9

20.7

21

21

21.1

21.8

8

Initial temperature of metal, °C

100

100

100

100

100

100

100

100

9

Equilibrium temperature of metal and water in calorimeter, °C

28.2

27.1

22.7

22.1

26.1

25.6

25.7

25.6

10

Δt water, °C

8

6.2

1.8

1.4

5.1

4.6

4.6

3.8

11

Δt metal, °C

-71.8

-72.9

-77.3

-77.9

-73.9

-74.4

-74.3

-74.4

12

qH2O, joules 1309.51 1283.36 302.84 293.65

853.15 962.75

769.50

794.99

13

Specific heat of the metal, joules/g °C

0.624

0.602

0.085

0.259

0.292

0.245

0.250

14

Approximat 40.06 e molar mass of metal, g/mol

41.53

294.12 304.88

96.53

85.62

102.04 100

0.082

B Heat of Solution: Unknowns

I

II

III

IV

V

302.30

303.49

259.22

303.89

303.39

1

Mass of calorimeter plus water, g

2

Mass of beaker, g

5.93

5.93

5.93

5.93

5.93

3

Mass of beaker plus solid, g

10.96

10.96

10.99

10.98

10.94

4

Mass of water, mH2O g

49.01

50.2

49.88

50.6

50.1

5

Mass of solid, g

5.03

5.03

5.06

5.05

5.01

6

Original temperature, °C

19.9

20.6

20.1

20.4

20.6

7

Final temperature, °C

14.5

27.8

14.5

16.5

25.6

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

3

8

qH2O for the reaction, (S.H. = 4.18 J/g °C), joules

-1106.25

1510.82

1167.59

824.88

1047.09

9

ΔH for the reaction, joules

1106.25

1510.82

1167.59

824.88

1047.09

219.88

-300.36

230.75

163.34

209

10 ΔH solution (joules/g)

Calorimeter= 253.29 C. Heat of Neutralization 1

Original temperature of HCl solution, °C

20.7

2

Original temperature of NaOH solution, °C

20

3

Final temperature of neutralized mixture, °C

32.7

4

Change in temperature (Δt), °C

12.35

5

qH2O, joules

2632.77

6

ΔH for the neutralization reaction, joules

-2632.77

7

ΔH per mole of H+ and OH− ions reacting, joules/mol

cannot be found

It was expected that the difference between the molar masses na d specific heat values calculated in two trials would be more close values to each other as only the volume of water has changed. However the average difference for every trial were 6.295 g/mol and 0.01575 joules/g °C in molar masses and specific heat values respectively. This difference could be explained by the heat loss to the environment during the transfer of metal to the calorimeter. Another explanation can be that during the experiment a lot of calculations were done; hence rounding to the certain decimal places can lead to inaccurate values after the number of calculations. In order to eliminate the large difference in values the experiment can be performed multiple times, and the average value can be calculated, which will make values more accurate. The objectives of the experiment were achieved as the molar masses and specific heat values of the four unknown metals were calculated by using the heat effect values, the heat of solution and neutralization were calculated.

III. APPENDIX Calculations A. Specific Heat: Δt water (t final − t initial)

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

4

A: Trial 1: 28.2-20.2=8 °C Trial 2: 27.1-20.9= 6.2°C B: Trial 1: 22.7-20.9=1.8°C Trial 2: 22.1-20.7=1.4°C E: Trial 1: 26.1-21=5.1°C Trial 2: 25.6-21=4.6°C H: Trial 1: 25.7-21.1=4.6°C Trial 2: 25.6-21.8=3.8°C Δt metal A: Trial 1: 28.2-100=-71.8°C Trial 2: 27.1-100=-72.9°C B: Trial 1: 22.7-100=-77.3°C Trial 2: 22.1-100=-77.9°C E: Trial 1: 26.1-100=-73.9°C Trial 2: 25.6-100=-74.4°C H: Trial 1: 25.7-100=-74.3°C Trial 2: 25.6-100=-74.4°C qH2O A: Trial 1: 39.16*4.18*8=1309.51 joules Trial 2: 49.52*4.18*6.2=1283.36 joules B: Trial 1: 40.25*4.18*1.8=302.84 joules Trial 2: 50.18*4.18*1.4=293.65 joules E: Trial 1: 40.02*4.18*5.1=853.15 joules Trial 2: 50.07*4.18*4.6=962.75 joules H: Trial 1: 40.02*4.18*4.6=769.50 joules Trial 2: 50.05*4.18*3.8=794.99 joules Specific heat of the metal A: Trial 1: -1309.51/(-71.8*29.24)=0.624 joules/g °C Trial 2: -1283.36/(-72.9*29.24)=0.602 joules/g °C B: Trial 1: -302.84/(-77.3*45.86)=0.085 joules/g °C Trial 2: -293.65/(-77.9*45.86)=0.082 joules/g °C E: Trial 1: -853.15/(-73.9*44.58)=0.259 joules/g °C Trial 2: -962.75/(-74.4*44.39)=0.292 joules/g °C H: Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

5

Trial 1: -769.50/(-74.3*42.18)=0.245 joules/g °C Trial 2: -794.99/(-74.4*42.63)=0.250 joules/g °C Approximate molar mass of metal A: Trial 1: 25/0.624=40.06 g/mol Trial 2: 25/0.602=41.53 g/mol B: Trial 1: 25/0.085=294.12 g/mol Trial 2: 25/0.082=304.88 g/mol E: Trial 1: 25/0.259=96.53 g/mol Trial 2: 25/0.292=85.62 g/mol H: Trial 1: 25/0.245=102.04 g/mol Trial 2: 25/0.250=100 g/mol B. Heat of Solution: qH2O I: 4.18*49.01*(-5.4)= -1106.25 joules II: 4.18*50.2*7.2=1510.82 joules III: 4.18*49.88*(-5.6)= -1167.59 joules IV: 4.18*50.6*(-3.9)= -824.88 joules V: 4.18*50.1*5=1047.09 joules C. Heat of Neutralization: qH2O=50.0*1.02*4.18*12.35=2632.77 joules qH2O=- ΔH for the neutralization reaction=-2632.77 joules

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

6

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

7

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

8

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

9

Department of Chemistry, School of Sciences and Humanities | General Chemistry Laboratory Report

10...