02-02-2013, 03:03 PM
Preparation of Soap
[attachment=49410]
Introduction
Soap, from a chemical standpoint, is a salt (or a mixture of salts) of fatty acids. As with all salts, soap contains a positive ion, usually Na+ or K+, and a negative ion, usually the anions of long-chained carboxylic acids obtained by the hydrolysis of animal or vegetable fats. These fatty acids, of which there are about 20 naturally occurring members, are carboxylic acids containing 14, 16, or 18 carbon atoms in an unbranched chain. The even numbered chains result from the
fact that fats are synthesized in cells by the polymerization of a 2-carbon acetate unit.
In addition to the normal (straight chain) saturated acids, there occur several with hydroxyl groups, and/or one or more double bonds in the carbon chain. the presence of unsaturation (double bonds) in molecules of fatty acids, fats, or soup tend to lower the melting point of these compounds and to cause them to be in the liquid state at room temperature. Thus, vegetable fats are relatively unsaturated and liquid under the ordinary conditions, while animal fats, being relatively more saturated, are solid, or semi-solid, at the same temperature. For this reason, vegetable fats are commonly refereed to as vegetable oils. (We say relatively saturated, or unsaturated because both vegetables oils and animal fats contain saturated and unsaturated chains). The reason why double bonds lower the melting point of a fatty acid chain, is that the sections of the chain attached to the double bond are attached cis-wise to each other (probably because the double bond cis configuration produces a bent chain which does not easily adhere to a neighboring chain by a Van der Waals attraction hence a lower temperature (lower mobility) is required for these molecules to adhere in order to form a solid crystal lattice. It is interesting to note, that straight chained carboxylic acids having an odd number of carbon atoms melt lower than even chained acids of comparable molecular weights.
Procedure
Two procedures for soap making are given, a “cold” and a “hot” process. The cold process, suitable for homemade soaps, produces soap bars which retain the glycreine by-product, and if the amount of alkali employed in the saponification is limited, an excess of fat (superfatted). The hot process, more suitable for laboratory or industrial preparation, yields a more chemically pure powder; by-products and excess starting materials are separated.
Cold process
You must wear goggles or glasses.
When using a thermometer in this experiment, never use it to stir liquids. Instead, use a fire polished glass rod. to properly measure the temperature of a liquid, hold the thermometer so that its bulb is suspended in the center of the liquid while reading the mercury level. If the liquid is being heated on a hot plate, do not the thermometer bulb to rest on the bottom of the container, as it will then be overheated. Remove the thermometer from the container after each reading. Note: the thermometer supplied does not require shaking down before or after reading. Plug in a hot plate and set to high.
Weigh a 150 ml beaker on the trip scale and add 8g of NaOH pellets to it. Handle NaOH with care as NaOH can burn the skin and is especially harmful to the eyes. In the hood, add 25 ml of cold water to the beaker. Stir the mixture of NaOH pellets and water, until a clear solution results. Caution: the beaker will become very hot as the NaOH dissolves.
Weigh a 250ml beaker on the trip-scale and add 58g of fat (Crisco vegetable shortening works well) to it. Then place the beaker on the hot plate with low heat and with occasional stirring, melt the fat to melt completely. Warm the melted fat to between 40-50 oC. Remove the fat from the hot plate and add the lye solution to the fat with stirring. Stir the fat and NaOH mixture continuously and until an emulsion is formed. Your mixture should look like a thick, light yellow milk shake and should stay emulsified (should not separate into a fat and NaOH layer). If your emulsion separates, the fat is too hot and needs to cool. Let the mixture cool on the bench top with occasional stirring until an emulsion, which does not separate, is formed. You may want to add perfume or other additives at this point. Pour the emulsion into a plastic cup and place in your drawer for the reaction to run (it takes about 24 hours for the reaction to be complete). Take the soap home with you and let age for about two weeks. During this time a powdery layer of NaCO3 (soda ash) will form on the surface, as residual NaOH reacts with CO2 in the air while the soap is drying. This powdery layer should be sliced off and the soap is ready to be used.
Hot process
You MUST wear goggles or glasses!
Plug in a hot plate and set it on HIGH. Half fill a 400 ml beaker with hot water from the sink and place on the hot plate. When the water begins to boil, adjust the heat, so that the water boils gently, but continuously. While waiting for the water to boil, weigh a 250ml Erlenmeyer flask on a triple beam balance and add 10g of fat (Crisco, spry, or lard) to it. In a 150ml beaker prepare 100 ml of a 50-50 solution of alcohol-water, by mixing 50 ml of water and 50 ml of 95% ethanol or methanol. Weigh another 150 ml beaker on the triple beam balance, and add 10g of NaOH pellets to the beaker. Handle NaOH with care as NaOH can burn the skin and is especially harmful to the eyes. In the hood, mix the NaOH with 36 ml of the of the 50-50 alcohol-water solution to it. Stir the mixture until a transparent solution is formed. Caution: the beaker will get very hot as the lye dissolves.
Pour the lye solution into the Erlenmeyer flask containing the fat and mix well using a stirring rod or by swirling with a beaker tongs. Clamp the Erlenmeyer in the boiling-water bath and with occasional stirring, allow it to cook for at least 30 minutes. While the mixture boils, some foam will form (due to soap formation). Try to minimize excessive foaming, by adding small adding small portions of your alcohol-water solution. The reaction is complete when oil globules are no longer visible when the reaction mixture is stirred.
Half fill a 600 ml beaker with 300 ml of clear (filtered) saturated salt (NaC1) solution and 50 ml of water. Pour the still hot reaction mixture containing soap, glycerine, excess NaOH, and alcohol into the salt solution. Stir the resulting mixture and allow to stand for 5-10 minutes. The soap will collect as a white layer on the surface of the salt water in the beaker.
Prepare a suction trap from the vacuum flask, which will be used later to filter the soap preparation. Bend a long piece of glass tubing into a right angle (instructor will demonstrate), and push one leg of the bend through a one-hole rubber stopper fitted for the mouth of the flask. When inserted, the glass tube should extend to about ½ inch from the bottom of the flask. The exposed leg of the bend should be cut off at about 3 inches from the bend, and, by means of a piece of rubber connector tubing, be attached to a 12-inch length of glass tubing. The side-arm of the vacuum flask is now connected to the vacuum outlet with pressure tubing. When the suction is turned on, this device will act like a vacuum cleaner, sucking up liquid instead of dust.
[attachment=49410]
Introduction
Soap, from a chemical standpoint, is a salt (or a mixture of salts) of fatty acids. As with all salts, soap contains a positive ion, usually Na+ or K+, and a negative ion, usually the anions of long-chained carboxylic acids obtained by the hydrolysis of animal or vegetable fats. These fatty acids, of which there are about 20 naturally occurring members, are carboxylic acids containing 14, 16, or 18 carbon atoms in an unbranched chain. The even numbered chains result from the
fact that fats are synthesized in cells by the polymerization of a 2-carbon acetate unit.
In addition to the normal (straight chain) saturated acids, there occur several with hydroxyl groups, and/or one or more double bonds in the carbon chain. the presence of unsaturation (double bonds) in molecules of fatty acids, fats, or soup tend to lower the melting point of these compounds and to cause them to be in the liquid state at room temperature. Thus, vegetable fats are relatively unsaturated and liquid under the ordinary conditions, while animal fats, being relatively more saturated, are solid, or semi-solid, at the same temperature. For this reason, vegetable fats are commonly refereed to as vegetable oils. (We say relatively saturated, or unsaturated because both vegetables oils and animal fats contain saturated and unsaturated chains). The reason why double bonds lower the melting point of a fatty acid chain, is that the sections of the chain attached to the double bond are attached cis-wise to each other (probably because the double bond cis configuration produces a bent chain which does not easily adhere to a neighboring chain by a Van der Waals attraction hence a lower temperature (lower mobility) is required for these molecules to adhere in order to form a solid crystal lattice. It is interesting to note, that straight chained carboxylic acids having an odd number of carbon atoms melt lower than even chained acids of comparable molecular weights.
Procedure
Two procedures for soap making are given, a “cold” and a “hot” process. The cold process, suitable for homemade soaps, produces soap bars which retain the glycreine by-product, and if the amount of alkali employed in the saponification is limited, an excess of fat (superfatted). The hot process, more suitable for laboratory or industrial preparation, yields a more chemically pure powder; by-products and excess starting materials are separated.
Cold process
You must wear goggles or glasses.
When using a thermometer in this experiment, never use it to stir liquids. Instead, use a fire polished glass rod. to properly measure the temperature of a liquid, hold the thermometer so that its bulb is suspended in the center of the liquid while reading the mercury level. If the liquid is being heated on a hot plate, do not the thermometer bulb to rest on the bottom of the container, as it will then be overheated. Remove the thermometer from the container after each reading. Note: the thermometer supplied does not require shaking down before or after reading. Plug in a hot plate and set to high.
Weigh a 150 ml beaker on the trip scale and add 8g of NaOH pellets to it. Handle NaOH with care as NaOH can burn the skin and is especially harmful to the eyes. In the hood, add 25 ml of cold water to the beaker. Stir the mixture of NaOH pellets and water, until a clear solution results. Caution: the beaker will become very hot as the NaOH dissolves.
Weigh a 250ml beaker on the trip-scale and add 58g of fat (Crisco vegetable shortening works well) to it. Then place the beaker on the hot plate with low heat and with occasional stirring, melt the fat to melt completely. Warm the melted fat to between 40-50 oC. Remove the fat from the hot plate and add the lye solution to the fat with stirring. Stir the fat and NaOH mixture continuously and until an emulsion is formed. Your mixture should look like a thick, light yellow milk shake and should stay emulsified (should not separate into a fat and NaOH layer). If your emulsion separates, the fat is too hot and needs to cool. Let the mixture cool on the bench top with occasional stirring until an emulsion, which does not separate, is formed. You may want to add perfume or other additives at this point. Pour the emulsion into a plastic cup and place in your drawer for the reaction to run (it takes about 24 hours for the reaction to be complete). Take the soap home with you and let age for about two weeks. During this time a powdery layer of NaCO3 (soda ash) will form on the surface, as residual NaOH reacts with CO2 in the air while the soap is drying. This powdery layer should be sliced off and the soap is ready to be used.
Hot process
You MUST wear goggles or glasses!
Plug in a hot plate and set it on HIGH. Half fill a 400 ml beaker with hot water from the sink and place on the hot plate. When the water begins to boil, adjust the heat, so that the water boils gently, but continuously. While waiting for the water to boil, weigh a 250ml Erlenmeyer flask on a triple beam balance and add 10g of fat (Crisco, spry, or lard) to it. In a 150ml beaker prepare 100 ml of a 50-50 solution of alcohol-water, by mixing 50 ml of water and 50 ml of 95% ethanol or methanol. Weigh another 150 ml beaker on the triple beam balance, and add 10g of NaOH pellets to the beaker. Handle NaOH with care as NaOH can burn the skin and is especially harmful to the eyes. In the hood, mix the NaOH with 36 ml of the of the 50-50 alcohol-water solution to it. Stir the mixture until a transparent solution is formed. Caution: the beaker will get very hot as the lye dissolves.
Pour the lye solution into the Erlenmeyer flask containing the fat and mix well using a stirring rod or by swirling with a beaker tongs. Clamp the Erlenmeyer in the boiling-water bath and with occasional stirring, allow it to cook for at least 30 minutes. While the mixture boils, some foam will form (due to soap formation). Try to minimize excessive foaming, by adding small adding small portions of your alcohol-water solution. The reaction is complete when oil globules are no longer visible when the reaction mixture is stirred.
Half fill a 600 ml beaker with 300 ml of clear (filtered) saturated salt (NaC1) solution and 50 ml of water. Pour the still hot reaction mixture containing soap, glycerine, excess NaOH, and alcohol into the salt solution. Stir the resulting mixture and allow to stand for 5-10 minutes. The soap will collect as a white layer on the surface of the salt water in the beaker.
Prepare a suction trap from the vacuum flask, which will be used later to filter the soap preparation. Bend a long piece of glass tubing into a right angle (instructor will demonstrate), and push one leg of the bend through a one-hole rubber stopper fitted for the mouth of the flask. When inserted, the glass tube should extend to about ½ inch from the bottom of the flask. The exposed leg of the bend should be cut off at about 3 inches from the bend, and, by means of a piece of rubber connector tubing, be attached to a 12-inch length of glass tubing. The side-arm of the vacuum flask is now connected to the vacuum outlet with pressure tubing. When the suction is turned on, this device will act like a vacuum cleaner, sucking up liquid instead of dust.