How to Prepare Detergent in a Chemistry Lab
Soaps and detergents represent members of a broad class of compounds known as surfactants, or "surface-acting agents." Technically, the soaps represent surfactants formed from natural products such as animal fats, whereas detergents represent synthetic or manmade compounds. Chemically, they comprise long-chain carbon molecules that consist of oil-soluble and water-soluble species on the molecules' opposite ends. When dissolved in water in the presence of dirt or oil particles, they form what chemists call micelles, in which the oil-soluble parts of the molecules dissolve into the oil and the water-soluble ends dissolve in the water. This behavior causes the oil to disperse into microscopically small droplets; in chemical terms, the detergent molecules "solubilize" the oil.
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Things You'll Need
- Rubber gloves
- 7.2 grams sodium hydroxide pellets, NaOH
- Water
- 150-mL glass beaker
- Glass stirring rod
- Phenolphthalein indicator solution
- 18 milliliters dodecanol, also known as lauryl alcohol
- 100-mL graduated cylinder
- 125-mL Erlenmeyer flask
- 10 milliliters concentrated sulfuric acid, H2SO4
- 10-mL graduated cylinder
- Round filter paper
- Glass funnel
- 250-mL Erlenmeyer flask
- Watch glass
- Large beaker
- Baking soda, also known as sodium bicarbonate
Instructions
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Put on rubber gloves, and prepare a solution of 6 M NaOH by dissolving 7.2 grams of solid NaOH pellets in about 30 mL of water in a 150-mL glass beaker. Stir the mixture with a glass stirring rod to dissolve the sodium hydroxide, and then add three drops of phenolphthalein indicator solution and stir it again. The solution should turn a bright violet color. Label the beaker "NaOH" and set it aside.
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2
Measure out 18 milliliters of dodecanol in a 100-mL graduated cylinder and transfer it to a 125-mL Erlenmeyer flask. Measure out 10 milliliters of concentrated sulfuric acid in a 10-mL graduated cylinder and slowly add it to the dodecanol while periodically swirling the flask to mix the contents and dissipate the heat. Label the flask "dodecanol/acid."
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Add the dodecanol/acid solution a few milliliters at a time to the NaOH solution in the beaker. Stir the mixture with a glass stirring rod between additions. When the violet color of the NaOH solution disappears, stop adding the dodecanol/acid solution, and stir the NaOH solution for 5 minutes.
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Fold a piece of round filter paper into quarters and place it in a glass funnel Then rest the funnel on the opening of an empty 250-milliliter beaker.
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Pour the NaOH solution from the beaker through the filter paper. Rinse any residue from the beaker with a small amount of water and also pour the rinse solution through the filter paper.
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Place the filter paper and its contents on a watch glass and allow it to air dry. The solid residue on the filter paper is detergent.
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Destroy any unused sulfuric acid solution by pouring it into a large beaker and slowly sprinkling it with baking soda, also known as sodium bicarbonate. When the acid no longer produces "fizz," it has been neutralized and can be poured down the sink.
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Tips & Warnings
Test your surfactant by putting equal amounts of your surfactant and commercial laundry detergent into 125-mL Erlenmeyer flasks, adding equal amounts of water and then swirling the solutions to produce "suds." Observe the time required for the suds in your detergent to subside versus the time required for the commercial detergent.
Concentrated sulfuric acid and sodium hydroxide pellets are corrosive. Do not allow them to contact bare skin, and wear safety goggles at all times when handling them.
References
- Case Western Reserve University, Nanopedia: Micelles
- University of Nebraska-Lincoln, Department of Chemistry: Soaps vs. Detergents
- Michigan State University, Department of Chemistry: Lipids
- Clemson University, College of Engineering and Science: Synthesis and Environmental Impact of Soap and Detergents
Resources
- Photo Credit Jupiterimages/Photos.com/Getty Images
