An Examination Of Material Balance With Chemical Reactions Biology Essay

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This section of the report gives a short summary of what is about to be seen in this report. Firstly, the objective of this experiment to use the principle of material balance to the reaction which is a batch reaction to obtain a conclusion on how different factors can affect the outcome of yield conversion and rate of reaction. The aim can help a student better understand how the experiment is to go about and what the main objectives help students better understand what they are doing and the hypothesis helps the students better figure out what the results are to be expected.

The theory helps to nurture the students with the experimental theory such as what saponification is how different factors affect the final outcome of the experimentation of the hydrolysis of an ester and an alcohol.

The procedure shows students how the main key points on conducting the experiment. Some of the key points discussed would be preparation of chemicals, experimental and procedure.

The next section would be the results and discussions part which shows the tabulated results that were obtained from the experiment conducted. The results and calculations include concentration readings taken for every 1 minute, yield, conversion and rate of reaction. The results shown are for both tests.

Following the results and calculations, a discussion is carried out stating experimental facts and how different factors can affect the rate of reaction, yield and conversion. The experiment carried out used concentration as a variable to find out how it affects the experimental results. In the end, concentration was ruled out to be a dependant factor that affects rate of reaction, yield and conversion as the higher concentration yields higher results.

Finally, conclusions are drawn from the results and calculations, and discussion. This section also tells whether the experimental objective and hypothesis was met accordingly. This section will also acknowledge on how optimum conditions can be obtained.

Introduction

Aim

The aim of this experiment is to allow students to employ the principles of material balance to a batch process to work out the conversion, reaction rate and yield. These three aspects are studied by using the rate of reaction of two different tests, two different concentrations of ethyl acetate with a constant concentration and volume of sodium hydroxide. This is done to find out whether concentration is a factor that affects the conversion, reaction rate and yield.

Hypothesis

For this experiment, three basic things are considered, conversion, yield and conversion. Between the two tests, the one utilizing the normal concentration is expected to obtain a lower conversion and yield. The conversion is expected to reach near45%-60%. The second test, using twice the concentration, is expected to achieve higher percentage on all three aspects.

Background Information

In the chemical process industries, many factors are taken into consideration to attain the maximum possible profit. The few main things that are taken in to consideration most are maximum yield and maximum conversion. Maximum yield is the most possible amount of product that you can obtain from the least amount of product. Maximum conversion refers to the total conversion of reactants to an extent that there aren't any left. This is important as in the industry the amount of products being used may be worth millions of dollars, so wasting even the smallest bit may cause a big loss, so they make the optimum conditions to achieve maximum conversion and maximum yield.

Theory

In this experiment, there are a few main factors that are discussed in the experiment of material balance with chemical reaction. The factors are:

Saponification

Saponification is the hydrolysis of an ester with a base to form an alcohol and the salt of an acid. In the industry, saponification is usually used as a process to form soap. However, in the industry the common reactants used would be a metallic alkali and fat or oil; in this experiment the reactants used are sodium hydroxide and ethyl acetate.

Batch process

A batch process is usually an unsteady -state operation, whereby not all of the conditions stay constant with time. An example of a batch process would be heating a kettle of water; the temperature does not stay constant with time. For this experiment temperature and pressure are kept constant. All the reactants are added into the reactor at start and only removed at the end of the experiment. So the amount of reactants (concentration) decreases with time (Singapore poly 2009/2010 CP 5047 Practical Notes).

Concentration

Concentration is the measure of solute in a given substance. In this experiment, concentration of ethyl acetate is the factor that would be kept as a variable. We would be having two tests, one with a normal concentration and the other with twice the concentration. This is done so to see how a change in concentration would affect the yield, conversion and rate of reaction in the experiment. Theoretically, having more particles would increase the chance for collision with other particles which induces reaction (Singapore poly 2009/2010 CP 5047 Practical Notes).

Yield

Yield is defined as the number of moles of product obtained per key reactant fed into reactant. In an industry, yield is important in any reaction, it is done so to obtain the most possible amount of product from the least amount of key reactant. To obtain a perfect yield, there must be optimum conditions. However, in this experiment we are keeping the most of the conditions constant except concentration. This is done to see how concentration affects the yield (Singapore poly 2009/2010 CP 5047 Practical Notes).

Conversion

Conversion is, by name, referred to as how much reactant has been converted into products. Like other factors mentioned before, this is also an important factor in any reaction. To find out how much reactant has been transformed into products is of upmost importance as in the industries reactants that are used may be worth a lot of money therefore, a minor waste of reactants may lead to the company's big loss. In this experiment, we would conversion factor to deduce how much of product has been formed and how much of the reactant was used up. Then, we will compare results from both experiments and draw conclusions on how concentration affects the conversion in an experiment (Singapore poly 2009/2010 CP 5047 Practical Notes).

Rate of reaction

Rate of reaction is defined as how fast an experiment reaches completion. In this experiment this is really important as Rate of reaction affects how much reactant is converted and how much product is formed in a certain time limit. A catalyst increases the rate of reaction but it is not used in this experiment as we are testing how a difference in concentration affects an outcome of an experiment (Singapore poly 2009/2010 CP 5047 Practical Notes).

Pressure

Pressure is a factor that affects the rate of reaction of an experiment. As pressure is increased, gaseous particles are much close to each other and thus collision is much often which means rate of reaction is increased. However this factor only affects gaseous substances, which alternatively means that increase in pressure does not necessarily affect the rate of reaction in solid or liquid substance. Therefore, pressure is not much a factor that affects the final results of this experiment. However the pressure is kept constant at 1 atm (Singapore poly 2009/2010 CP 5047 Practical Notes).

Conductivity

Conductivity of a solution is the ability for the solution to conduct electricity. In industries, conductivity values are used as a fast, inexpensive and reliable way to measure ionic content in a solution. The SI unit for conductivity is Siemens per metre(S/m). In this experiment, we would be measuring the conductivity values for sodium hydroxide. The conductivity values of sodium hydroxide are measured instead of the other reactant and products as ethyl acetate, sodium acetate and ethanol have negligible conductivity value. (Singapore Polytechnic 2010) The conductivity is measured by a conductivity probe. Then the concentration can be calculated from the Conductivity Concentration graph.

(Singapore poly 2009/2010 CP 5047 Practical Notes)

Procedure

3.1 Preparation of chemicals

There are only two chemical reactants that are to be used in this experiment. The Material Safety Data Sheet (MSDS) of ethyl acetate and sodium hydroxide should be read carefully before the start of the experiment. Safety is the no. 1 concern in this experiment therefore goggles and gloves are to be used from the start of experiment to the end. The concentrations and volume of chemicals to be used have been calculated during the pre-experiment procedure of the experiment.

Firstly, the working solution of NaOH should be prepared. The required concentration and volume is 0.01M and 500mL respectively. The available stock solution has a concentration of 0.1M, which means that 50mL from stock solution has to be diluted to 500mL. 50mL of stock solution is to be poured into the 500mL volumetric flask and filled to the 500mL mark with de-ionised water. The volumetric flask is then capped and then shaken well to ensure thorough mixing.

Next, the working solution of ethyl acetate should be prepared. The required volume and concentration is 500mL and 0.01M respectively. Firstly, the volumetric flask is filled 250mL of de-ionised water. Next, the calculated amount of pure ethyl acetate is added. Finally, the volumetric flask is filled to the 500mL mark with de-ionised water. The volumetric flask is then capped and shaken well.

The same working solutions are made once more for the second test. All concentrations are kept the same except the working solution of ethyl acetate which uses twice the concentration.

3.2 Experimental setup

The experimental setup is shown as below (Singapore poly 2009/2010 CP 5047 Practical Notes)

3.3 Procedure

The prepared reactants are poured into the reactor with conditions such as temperature, concentrations and volume taken note of. The conductivity probe should be placed in the middle of the reactor as the middle is where the real reaction occurs. The timer is started once all the reactants are in the reactor. From here, reading is taken every 1 min for half an hour. After the 30mins, the magnetic stirrer is stopped. All equipment that came into contact with the products is washed with de-ionised water. The mixture in the reactor is poured away into a chemical waste basket. After the drying of equipment, the experiment is carried out with the second concentration as discussed earlier. After the second set, the workplace was cleared and all unused chemicals and equipment were returned to the lab technician.

Results and Calculations

This is the first set of results that were obtained, Concentration of ethyl acetate used: 0.01M

Timing No. (Mins)

 Conductivity of NaOH (µS/cm)

Concentration of NaOH (M)

1

1105

0.00326

2

1072

0.00307

3

1051

0.00295

4

1030

0.00283

5

1012

0.00272

6

995

0.00263

7

977

0.00252

8

964

0.00245

9

948

0.00235

10

933

0.00227

11

919

0.00219

12

907

0.00212

13

893

0.00204

14

881

0.00197

15

869

0.0019

16

859

0.00184

17

849

0.00176

18

839

0.00173

19

829

0.00167

20

819

0.00161

21

809

0.00155

22

801

0.00151

23

793

0.00146

24

785

0.00141

25

775

0.00136

26

769

0.00132

27

761

0.00128

28

755

0.00124

29

747

0.00119

30

741

0.00116

This is the second set of results that were obtained, Concentration of ethyl acetate used: 0.02M

Timing No. (Mins)

 Conductivity of NaOH (µS/cm)

Concentration of NaOH (M)

1

1080

0.0031

2

1040

0.0029

3

1005

0.0027

4

972

0.0025

5

942

0.0023

6

816

0.0022

7

889

0.002

8

866

0.0019

9

844

0.0018

10

824

0.0016

11

804

0.0016

12

786

0.0014

13

770

0.0013

14

754

0.0012

15

740

0.0012

16

726

0.0011

17

712

0.001

18

700

0.00092

19

688

0.00085

20

678

0.0008

21

666

0.00073

22

658

0.00068

23

648

0.00062

24

640

0.00057

25

630

0.00052

26

622

0.00047

27

616

0.00044

28

608

0.00039

29

600

0.00035

30

596

0.00032

From the results obtained it is possible to draw out a graph to better illustrate the finding of the experiment.

Graph from first experiment:

Graph from second set of results:

Since we have drawn the appropriate graphs, we can now find the conversion and yield.

Conversion:

From Graph A:

Original No. of Moles of NaOH (start of experiment): 0.005mol

No. of moles after 15 minutes (midway of experiment): 0.001898mol

No. of moles reacted: 0.005mol-0.001898mol = 0.003102mol

X = (0.003102/0.005)*100%

= 62.04 %

From Graph B:

Original No. of Moles of NaOH (start of experiment):0.005mol

No. of moles after 15 minutes (midway of experiment): 0.00115mol

No. of moles reacted: 0.005mol-0.00115mol =0.00385mol

X B= (0.00385/0.005)*100%

= 77%

Yield:

Given that stoichiometric ratio of the equation is 1:1

The no. of moles of desired products formed is equal to the no. of moles reacted.

From Graph A,

Original No. of Moles of NaOH (start of experiment): 0.005mol

No. of moles after 15 minutes (midway of experiment): 0.001898mol

No. of moles reacted: 0.005mol-0.001898mol = 0.003102mol

Therefore, no. of moles of product formed: 0.003102mol

Yield= 0.003102 / 0.005

= 0.6204

From Graph B

Original No. of Moles of NaOH (start of experiment):0.005mol

No. of moles after 15 minutes (midway of experiment): 0.00115mol

No. of moles reacted: 0.005mol-0.00115mol =0.00385mol

Therefore, No. of moles of product formed: 0.00385mol

Yield = 0.00385 / 0.005

= 0.77

Discussion

5.1 Factors affecting Conductivity

For this experiment, the only variable was the concentration of ethyl acetate. However, the conductivity probe used was able to measure only the conductivity value of NaOH. But by using a higher concentration of ethyl acetate, it seemed that the conductivity value was decreasing at a much faster rate than that of normal concentration.

5.2 Factors affecting Rate of Reaction

In this experiment, we are trying to find out how a change in concentration affects the reaction rate. From the results obtained, it is proved that concentration does affect the rate of reaction in a reaction. A higher concentration increases the rate of reaction; this can be proven as due to higher concentration means that there are more particles for collision, therefore reaction occurs more often. This experiment was done solely to show that concentration is a factor that affects rate of reaction by keeping other factors such as temperature and pressure were kept constant.

5.3 Yield and Conversion

In this experiment, it is impossible to obtain a 100% conversion or yield. There are many reasons to account for this phenomenon. Firstly, there is a time restriction of 30 min, which prevents conversion and yield to reach 100%. Secondly, during the conduct of experiment, there might have been human errors that cannot be prevented. However since this was a controlled test, this was to be the result. But if the experiment were to have a catalyst added, there might be a possibility that the yield and conversion would have gotten a full 100%.

If we were to compare the yield from the first experiment and second experiment, we can see that the second experiment has a higher yield as compared to the first one. This is due to the increased concentration of ethyl acetate which gives way to more reaction occurrence. This goes same for conversion, whereby the second experiment gave a higher conversion rate.

Conclusion

From this experiment, one acquires knowledge of how a batch reaction of saponification occurs. We also gain the knowledge of the different factors that affect a reaction. In this experiment, we embarked on finding out whether concentration is a factor that affects the final results of yield, conversion and rate of reaction in an experiment. After obtaining the raw data and applying a few calculations it is proved that concentration does play a very important factor in the experiment. From the experiment results, we find that the hypothesis was proven correct we also find that all the experiment objectives were met. However, this experiment would have gone better if the elimination of human error was done, which means that all the procedure should be done by computers to achieve a more accurate result.

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