Testing the Effectiveness of Fuels

Aim

To test the effectiveness of different fuels by determining the enthalpy change from burning of the fuel.

Procedure

Use the steps below for each fuel tested, namely methanol and cyclohexane.

1. Place a piece of cotton wool in a dry crucible.

2. Measure 10ml of the fuel using a measuring cylinder and pour it into the crucible.

3. Measure 10ml of distilled water with another measuring cylinder and pour it into a clean 50ml beaker.

4. Secure the beaker of water using a retort stand directly above the crucible.

5. Measure and record the initial temperature of the water.

6. Light the fuel with a burning splint and start the stopwatch.

7. Adjust the height of the beaker accordingly so that the bottom of the beaker is at the tip of the flame.

8. After 2 minutes, measure and record the new temperature of the water. Extinguish the flame by smothering it with a wire gauze.

Results

                           Initial temp/°C      Final temp/°C         Change in temp/°C
Methanol            31.0°C                  75.0°C                    44.0°C      
Cyclohexane      31.0°C                  100.0°C                  69.0°C

Analysis

Q = mc∆T

Enthalpy change of water = mass of water (kg) x specific heat capacity of water (kJ/kgK) x change in temperature (°C)

Specific heat capacity of water = 4.181 kJ/kgK

                           Enthalpy change of water

Methanol            0.01 x 4.181 x 69 = 2.88489 kJ                       

Cyclohexane      0.01 x 4.181 x 44 = 1.83964 kJ

Amount of fuel in moles

Density of methanol = 791.30kg/m3                   

Mass of 10 ml of methanol = 791.30 x 10/1003 x 1000 = 7.931 g

No. of moles of methanol (CH₃OH) = 7.931/(12.0 + 4 x 1.0 + 16.0) = 0.24728 mol (5 s.f.)

Density of cyclohexane = 779.00 kg/m3

Mass of 10 ml of cyclohexane = 779.00 x 10/1003 x 1000 = 7.79 g
No. of moles of cyclohexane (C₆H₁₂) = 7.79/(6 x 12.0 + 12 x 1.0) = 0.092738 mol (5 s.f.)

                           Enthalpy change of water per mol of fuel

Methanol            2.88489/0.24728 = 11.7 kJ/mol (3 s.f.)                       

Cyclohexane      1.83964/0.092738 = 19.8 kJ/mol (3 s.f.)

Conclusion

Cyclohexane is a more efficient fuel than methanol.

Possible sources of error

1. Heat from the flame and water may have been lost to the surrounding, affecting the results.

2. For methanol, the water started boiling before 2 minutes was up, but since boiling water cannot exceed 100°C, measurements for methanol may be inaccurate. 

Extracting Limonene from Orange Peel

Aim

To extract the essential oil limonene (D-limonene) from orange peel using steam distillation.
Note: there are two isomers of limonene, D-limonene and L-limonene. They are stereo-isomers. D-limonene smells like citrus while L-limonene smells like turpentine.

Procedure

1. Cut and discard away the white pith from the orange peel, leaving the orange rind, as the orange portion contains the limonene.

2. Measure and record the mass of the orange peel in a clean pre-weighed container.

3. Blend the orange peel with a suitable amount of distilled water until a smooth, thick texture is achieved.

4. Transfer all the blended mixture into a clean 250ml round-bottomed flask using a spoon and filter funnel.

5. Set the steam distillation apparatus as shown. Turn on the hotplate and tap water for the condenser. Observe the temperature of the vapour as indicated in the thermometer.

6. Collect the distillate in a clean beaker.

7. Transfer the distillate into a clean boiling tube and immerse it into a hot water bath of 80°C. When distillate settles, the limonene will rise to the top of the tube, forming two distinct layers with water at the bottom.

8. Pour the limonene at the top of the tube into a clean pre-weighed test tube. Measure and record the mass of the limonene.

Results

Mass of orange peel used/g = 50.50g
Mass of D-limonene extracted/g = 1.20g

Percentage yield = 1.20/50.50 x 100 = 2.38% (2 d.p.)

Although the process is not very efficient, D-limonene is considered to have a rather high percentage yield as most essential oils usually have a percentage yield of 0.5% to 2%.

Behind the scenes

Essential oils like D-limonene are beneficial because they carry anti-carcinogenic properties and have multiple purposes, such as in cleansing products. Furthermore, the orange peel that we usually throw away can now be reused to produce D-limonene, a biofuel.

The process used in extraction of D-limonene is steam distillation. This does not denature the existing structure of D-limonene, but instead the hot steam opens up pockets in the orange peel containing the oils. Aromatic molecules of the volatile oil then escapes from the peel, forming vapours before condensing.

An Introduction to Green Chemistry

What is Green Chemistry?

Green Chemistry is sustainable chemistry, based on chemical research that promotes products and processes which minimise the use and generation of hazardous substances. Below is a venn diagram that defines sustainability.

Taken from http://www.vanderbilt.edu/sustainvu/who-we-are/what-is-sustainability/

Thus, unlike simply recycling or reusing waste, Green Chemistry aims to reduce and prevent pollution at its source, in order to create high-quality products that are energy efficient as well as environmentally friendly.

Often, green chemists follow the 12 principles of Green Chemistry during the process of their research, which is stated as follows.

1. Prevention
   It is better to prevent waste than to treat or clean up waste after it has been created.
2. Atom Economy
   Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
3. Less Hazardous Chemical Syntheses
   Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
4. Designing Safer Chemicals
   Chemical products should be designed to affect their desired function while minimizing their toxicity.
5. Safer Solvents and Auxiliaries
   The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.
6. Design for Energy Efficiency
   Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.
7. Use of Renewable Feedstocks
   A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.
8. Reduce Derivatives
   Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste.
9. Catalysis
   Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
10. Design for Degradation
    Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.
11. Real-time analysis for Pollution Prevention
    Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
12. Inherently Safer Chemistry for Accident Prevention
    Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.

Nowadays, different companies from all over the world are spending more money and effort on the research of Green Chemistry, such as biofuels, since sustainability is increasingly becoming an essential part of businesses and production. Hopefully, Green Chemistry can offer us a solution to the ever-increasing needs of the human population, while Earth's resources are rapidly depleting.