Materials Included In Kit

Additional Materials Required

Safety Precautions

Phenolphthalein indicator solution contains alcohol and is a flammable liquid; it is toxic by ingestion. Do not use near flames or other sources of ignition. The base extracted from wood ash is slightly toxic by ingestion and skin absorption and is irritating to skin and eyes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the lab.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding.

Teacher Tips

• In addition to demonstrating the application of several of the principles of green chemistry, this experiment can serve as a substitute for the traditional acid-base titration lab, which typically reacts HCl with NaOH to a pink endpoint.
• As an extension, use wood ash from different sources and compare how the different samples equate to each other and NaOH. Also, run a titration in parallel using NaOH to observe directly the amount of NaOH needed to titrate an equivalent amount of KHP.
• As an extension, vary the temperature of the water used to extract base from the wood ash to determine effects on the endpoint of the titration. Also, compare the end point achieved from base obtained from the first extraction to a second or third extraction. Do these two things together to maximize the extraction, that is, to derive as much base from the wood ash as possible.
• As an extension, evaporate the base down to use as a catalyst in the preparation of biodiesel.
• You can get additional wood ash from your fireplace, a pizza parlor that uses a wood oven, a fireplace store or a store that sells wood stoves. It is necessary to strain the wood ash with a colander to remove bits of charcoal, foreign matter, etc. It is recommended that the ash be strained twice. It is advisable to do this outdoors since a great deal of dust is usually produced. Use protective equipment such as a mask to avoid exposure to dust. The grey/white ash is what is needed—black charred wood should be kept to a minimum. If you choose to use wood ash from a fire pit make sure that it is dry and has never been rained on.

Sample Data

Moles base = Moles Acid = 0.070 g x 1 mole KHP/204.22 g = 3.43 x 10^–4 moles KHP
Volume base needed to reach endpoint (L) x Molarity base = moles KHP
Molarity base = moles KHP/Volume base needed to reach endpoint (L)
= 3.43 x 10^–4 moles/0.0202 L = 0.0170 M

Answers to Questions

1. Determine the NaOH base equivalence by multiplying the moles of wood ash by the molar mass of NaOH.

   moles wood ash = 0.0170 M x 0.250 L = 0.00425 moles wood ash
   NaOH base equivalence: 0.00425 moles wood ash x 40.0 g/1 mole = 0.170 g

2. Determine the wood ash to base equivalence by dividing the answer to Question 1 by the mass of wood ash used. This represents how much wood ash is needed to extract a given amount of base.

   0.170 g/50.37 g = 0.00338

3. To make 1L of biodiesel from fresh vegetable oil, about 4g of NaOH is needed. What mass of ash would be needed to obtain sufficient base to make 100 gallons of biodiesel?

   100 gallons biodiesel x (1 L/0.264 gallons) x (4 g NaOH/1 L biodiesel) x (50.37 g wood ash/0.170 g NaOH) = 448,930.48 g wood ash = 448.93 kg wood ash

4. Wood ash found at an old campsite would not work well for this method. Why not?

   Wood ash found at an old campsite will likely have spent significant time exposed to the elements, in particular rain and moisture. As a result some of the base will be extracted from it naturally over time and the wood ash will be less and less equivalent to NaOH. That is, less base will be extracted from wood ash found at an old campsite than from fresh wood ash.

5. Discuss how the use of wood ash as catalyst in the production of biodiesel aligns with the principles of green chemistry. Use the descriptions of the 12 principles of green chemistry found in the introduction section as a reference.

   To prepare biodiesel from vegetable oil base is needed as a catalyst. This experiment examines the extent to which wood ash can be used as a substitute for NaOH and aligns with several of the principles of green chemistry, as detailed.

   • Prevention: waste wood ash is still useful for the extraction of base; left over wood ash can be recycled/composted, and base isolated can be used in further preparation of biodiesel.
   • Use of Renewable Feedstocks: used wood ash as a base that can be used with another renewable feedstock (vegetable oil) to produce biodiesel.
   • Safer Solvents and Auxiliaries: no organic solvents were used.
   • Design for Energy Efficiency: experiment was run at ambient temperature and pressure.

References

Credit: Irv Levy, Department of Chemistry, Gordon College

Anastas, P.T.; Warner, J.C. Green Chemistry: Theory and Practice, Oxford University Press: New York, 1998.

Introduction

The 12 Principles of Green Chemistry guide us to use catalysts to improve the energy and atom efficiency of reactions. The principles also guide us to use renewable feedstocks. In this experiment, we can see how waste from one process can be used productively in another. Specifically, biodiesel can be made from waste vegetable oil, a renewable feedstock that was traditionally discarded by the food preparation industry. To prepare biodiesel from the vegetable oil, base is needed as a catalyst. In this lab we will focus on the catalyst and its source from another “waste material”—wood ash, the material left following the combustion (burning) of wood.

Concepts

• Acid–base titrations
• Renewable feedstocks
• Green chemistry
• Catalysis
• Extractions

Background

Much of what makes this world modern is the result of the application of chemistry and chemical reactions. Oil and gasoline, prescription drugs, plastics, solvents and fertilizers, to name a few, are all products of chemistry. Over time, many of the processes used to create these products were found to have unintended consequences and be quite harmful, whether to workers, the consumers or to the environment. In response to these pressing issues, green chemistry was developed as an approach to creating safer chemical products and processes from the initial design stage. The principles of green chemistry provide a framework for scientists to use when designing new materials, products, processes and systems. The principles focus on sustainable design criteria and provide tools for innovative solutions to environmental challenges. These principles are listed\.

• Prevention: It is better to prevent waste than to treat or clean up waste after it has been created.
• Atom Economy: Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product, leaving few or no atoms behind. 
• Less Hazardous Chemical Syntheses: Synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment. 
• Designing Safer Chemicals: Chemical products should be designed to be fully effective while minimizing or eliminating their toxicity. 
• Safer Solvents and Auxiliaries: Minimize the use of auxiliary substances (e.g., solvents, separation agents) wherever possible and make them innocuous when used. 
• 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. 
• Use of Renewable Feedstocks: Renewable raw material or feedstock should be used whenever technically and economically possible. 
• 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 additional waste. 
• Catalysis: Catalytic reagents are superior to stoichiometric reagents. 
• Design for Degradation: Chemical products should be designed so that at the end of their function they break down into innocuous products that do not persist in the environment. 
• 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. 
• 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.

Experiment Overview

Wood ash has been used as a valuable source of base throughout history. In this experiment we will extract the basic substances from a sample of wood ash and then determine their base potential compared to sodium hydroxide, the base often used in the production of biodiesel.

Materials

Safety Precautions

Phenolphthalein indicator solution contains alcohol and is a flammable liquid; it is toxic by ingestion. Do not use near flames or other sources of ignition. The base extracted from wood ash is slightly toxic by ingestion and skin absorption and is irritating to skin and eyes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the lab.

Procedure

Part A. Preparation of Ash Water (Base) 

1. Put a small beaker on the balance, then place an opened fluted filter paper into the empty beaker, and zero the balance.
2. Scoop about 30–50 g of wood ash into the filter. Accurately record the mass of the wood ash.
3. Transfer the wood ash from the filter paper to a 400-mL beaker. Do this gently to avoid making a lot of dust. Don’t worry if a little of the ash sticks to the filter paper.
4. Add 150-mL deionized water to the ashes in the beaker. Do this slowly to avoid making a lot of dust. Stir the resulting slurry with a glass stirring rod for about 1 minute.
5. Suspend a funnel over a 300-mL Erlenmeyer flask, placing the filter paper used in the earlier step inside the funnel.
6. Stir the ash water beaker well and pour as much as possible into the funnel without overflowing the filter paper. Don't worry if a little bit of ash gets into the filtered water. Wait until some of the liquid drains through the funnel then stir the slurry again and pour more into the funnel. Repeat until all of the slurry has been poured into the filter.
7. At this point it is likely that some of the ash is still in the beaker. If so, scrape as much as possible into the filter.
8. Obtain an additional 100-mL deionized water and use it in several small portions to rinse the residue from the beaker into the filter.
9. After the dripping stops and no liquid is visible in the ashes in the filter, remove the filter paper and discard the used ashes as directed by your instructor.
10. Obtain a new fluted filter paper and filter the ash water from the Erlenmeyer flask into a 250-mL volumetric flask. Add deionized water as needed to bring the 250-mL volumetric flask to the mark. (Remember to measure the volume by looking at the bottom of the meniscus.) The ash water is now ready for titration.

1. Label two 50-mL Erlenmeyer flasks A and B.
2. Zero a piece of weighing paper and obtain approximately 70 to 80-mg (0.070 to 0.080 g) of potassium hydrogen phthalate (KHP) acid.
3. Record the exact mass of the KHP.
4. Transfer the KHP to Erlenmeyer A.
5. Repeat steps 2 and 3 and transfer the KHP to Erlenmeyer B.
6. Add about 10-mL deionized water to the KHP in each flask and swirl to dissolve the solid.
7. Add 2 drops of phenolphthalein indicator to the acid solution in each flask and set aside.
8. Fill a 50-mL buret with filtered ash water, taking care to remove the air bubble from the tip.
9. Place a white sheet of paper under the 50-mL flask containing the acid so you can clearly see the color change. 10. Titrate the KHP solution with filtered ash water quickly with flask A to estimate the endpoint of the reaction.
10. Repeat the titration slowly with flask B to get an exact reading, to a light pink end point.
11. Calculate the molarity of the ash water base, using the fact that at the titration endpoint the moles of acid equals moles of base.

Student Worksheet PDF

14087_Student1.pdf