Practical on Enthalpy Changes Between Acids and Bases Essay

Published: 2020-01-28 23:51:56
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Category: Acid

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Introduction

All life on earth depends on the transfers of energy in chemical reactions. So that measurements can be made when energy is transferred during chemical reactions, that have to be carried out under controlled conditions. A special name is given to process where energy is transferred and exchanged with the surroundings, when taking place under constants pressure. The special name given to this type of process is Enthalpy.

When chemical reactions take place they release energy to the surroundings. There are also special names given to these kind of energy transfers. They are called exothermic and endothermic reactions. Out of these two types exothermic reactions are most easily detected. This is because in exothermic reactions energy is realised to the surroundings and is detected by temperature rise. But some chemical reactions only occur when energy is put into them from an external source. Reactions which require this sort of input are called endothermic reactions.

Enthalpy is the total energy content of the reacting materials. The symbol for enthalpy is ?H. Enthalpy is measured during a reaction. Energy is transferred to and from a reaction system and as a result the enthalpy changes. The equation used to calculate the enthalpy is as follows.

? H = mc ?T

(H is the enthalpy change, M is the mass of the reacting solution and C is the specific heat capacity for water.)

Acids are known as proton donors. Acids have a pH below 7 which varies from one acids to another. What I mean by this is that a strong acid readily gives away protons and is fully ionised in water. A weak acid is reluctant to give up its protons and is slightely ionised by water. Bases are on the other hand the total chemical opposites of acids they are proto acceptors. carry out was to an practical where an acid is basically reacted with a base and the heat produced by the reaction recorded.

Health and Saftey

During this practical a white lab coat should be worn and safety glasses du the use of acids could be dangerous.

Method

Refer to sheet given by lecturer

Results

Strengths

Solutions

pH of solutions

A2

1M Hydrochloric acid

0.68

A1

1M Sulphuric acid

0.32

A3

1M Ethanoic acid

2.42

B1

1M Sodium hydroxide

13.38

B3

1M Sodium hydrogen carbonate

8.42

B2

1M Ammonia

11.39

Key

A1 = Strongest acid

A3 = Weakest acid

B1 = Strongest base

B3 = weakest base

Acid

Base

T1 (Temp ?C)

T2 (Temp ?C)

Temp change (?C)

? H = mc ?T

HCl with

NaOH

23

30

7

-1170.4

2NaHCO3

23

28

5

-836

NH3

23

29

6

-1003.2

H2SO4

NaOH

22

27

5

-836

2NaHCO3

22

23

1

-167.2

NH3

22

25

3

-501.6

CH3CH2OH

NaOH

21

27

6

-1003.2

2NaHCO3

21

20

+ 1

167.2

NH3

21

25

4

-668.8

Conclusion

After successfully completing my experiment I have concluded a number of things. From my results I have results concluded that there is a relationship in our results to a certain degree. For example the enthalpy for each acid is as follows. The most strongest acid sulphuric acid, which had the lowest pH showed that when mixed with the base sodium hydroxide it gave the highest enthalpy value then the second strongest acid compared to the same base and then the third acids which was the weakest. This showed me that as the acid got weaker the enthalpy values also decreased.

The way in which I kept my experiment a fair test was that I made sure that I used the same equipment for example to use the same thermometer each time I made a temperature recording at the start of a reaction and at the end and made sure that each time the thermometer came back to its original temperature. Also I made sure that we used the same digital pH meter and that it was washed everytime after use to remove all impurities so contamination would not occur. Another important aspect was to make sure that the experiment was carried out in the same conditions because if for example the temperature changed this could have affected our practical and results. If I was to conduct this experiment again I would make a number of changes.

Firstley one point in the practical which I thought caused chance of error was when reading the meniscus line on the cylinder it was very hard to get this exactly right. A better and more accurate way would have been if we used an pipette it would have made it more accurate. I think another aspect which could cause error was the thermometer which could have used a digital one. And also finally there could have been another area in which error could have been caused is the pH meter this if not cleaned properly could infected my other solutions.

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