Introduction: (Initial Observation)
Solubility and the percent of oil in fruits are two important factor that affect the value of the fruit as food. Factories which extract oil from nuts and fruits such as almond, olive and corn need to know the percent of oil in these products before they are able to evaluate the price. Food laboratories frequently perform such experiments.
Many chemical analyses, especially those involving the separation of substances, depend on the appropriate choice of solvent. Foods such as peanuts are mixtures of different chemicals. Peanuts contain, among other things, proteins and oil. One method for separating these components is based on solubility differences.
Find out about peanut and the ways that you may extract peanut oil or other ingredients. Read books, magazines or ask professionals who might know in order to learn about solubility as a separation method. Keep track of where you got your information from.
Following are samples of information that you may find:
The peanut is native to South America. It grows on a leafy vine and is a member of the pea family. The nut-like seeds have a high protein content and they are a source of vitamin D and the B-complex vitamins, without having cholesterol. Peanut oil is favored by chefs everywhere for the fine taste it gives to fried foods. Peanut oil is also used in medicine, soaps, and rubbing or massage oils.
Peanuts are not really nuts. Nuts grow on trees. Peanuts are legumes, related to beans and peas. Peanuts grow underground.
The peanut is the fruit of the plant. It is unusual for the fruit of a plant to grow underground, especially when the flowers grow above ground.
The peanut seeds grow from a small green bush about 18 inches tall. This bush has delicate yellow flowers. After the flower loses its petals, the flower stalk, or peg, is pulled by gravity toward the ground. The peg grows into the ground and forms peanuts about one inch below the soil surface. It takes about four to five months for the peanut plant to grow from planting to harvest.
People eat large numbers of peanuts in the form of nuts, peanut butter, candy bars and baked goods. Other peanuts are crushed to extract peanut oil. Peanut oil is usually more expensive to use in cooking than other oils. However, since it has no flavor and no cholesterol and can be heated to a higher temperature without smoking, it is used by many restaurants for frying foods. It is also used in margarine, shortening and salad oil.
Peanuts are 25 to 30 percent protein and about 50 percent oil. The meal that remains after the oil is extracted from peanuts makes an excellent feed for cattle, hogs and poultry because of the high protein content. In early days, peanuts were grown as feed. Hogs, in particular, like peanuts and will root out the nuts themselves if turned into the peanut fields. Whole peanuts are seldom used for animal feed today because peanut growers can make more money selling them for people to eat. Some other names for the peanut are “groundnut,” “pinder” and “goober.”
The extent to which one substance will dissolve in another depends on the structural properties of both substances. One such property is the degree of polarity in a molecule. For example, water is a highly polar molecule which exhibits strong intermolecular forces called hydrogen bonds. A rule of thumb is that “like tends to dissolve like.” Thus water will tend to dissolve other polar substances, including salts. This has great biological significance since most biochemical reactions occur in an aqueous medium. However, some molecules have both polar and nonpolar ends, and it is sometimes difficult to predict the solubility of these substances in various solvents. Some of these substances have great practical use. For example, detergents are molecules which can dissolve in water, but they also have a nonpolar portion which dissolves in oil. Water solutions of detergents can therefore form emulsions with oils and fats.
NAME: Hexane (n-Hexane)
SYNONYMS: n-Hexane; Hexyl hydride; Normal hexane
Chemical Formula: CH3(CH2)4CH3
n-Hexane is a petroleum distillate used as a solvent in vegetable oil extraction, and in cleaners, degreasers, glues, spray paints, paint thinners, coatings, silicones, and greases. These n-hexane-containing products are often used by workers in the food processing, printing, manufacturing, painting, and automotive repair industries as well as anywhere petroleum distillates are used.
Commercial or technical grade hexane (the form used in most products) contains varying amounts of n-hexane (20-80%) along with other related compounds, and should be treated as pure n-hexane. Pure n-hexane is used in laboratories. Both n-hexane and mixed hexanes are often referred to as “hexane” and sometimes as “petroleum distillate” and are listed on Material Safety Data Sheets (MSDSs) with the CAS # 110-54-3.
HAZARDS: DANGER! EXTREMELY FLAMMABLE LIQUID AND VAPOR. VAPOR MAY CAUSE FLASH FIRE. HARMFUL OR FATAL IF SWALLOWED. HARMFUL IF INHALED. CAUSES IRRITATION TO SKIN, EYES AND RESPIRATORY TRACT. AFFECTS THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to determine what type of solvents can be used to dissolve (and extract) different types of solutes.
Perform experiments to determine the solubility of a variety of solutes in several solvents. The observed solubility will be related to the structure and intermolecular forces of both the solute and solvent. On the basis of these tests, you will then devise and carry out an experimental method for the determination of the percent of oil in peanuts.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Test the solubility of different substances such as sodium chloride (table salt), glycerin, citric acid, naphthalene (moth flakes), sugar, monosodium glutamate, gelatin, and vegetable oil.
For each solubility test that you perform, following are the variables.
Independent variable (also known as manipulated variable) is the solvent. Possible values are water, hexane, ethanol, and acetone.
Dependent variable (also known as responding variable) is the solubility rate. (Solubility rate may be measured or estimated visually)
Constants are the experiment method.
Controlled variables is the temperature.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
For the first part of your project, write your hypothesis in the form of a table like this:
Fill up the table with S for soluble, I for insoluble, SS for slightly soluble. Note that this table is just your hypothesis and you may later find out that some of your predictions have not been correct.
As your hypothesis for the second part of your project write which solvent you think will best dissolve the peanut oil.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1: SOLUBILITY TESTS
In this experiment, you will test the solubility of sodium chloride, glycerin, citric acid, naphthalene, sugar (sucrose), monosodium glutamate (MSG), gelatin, and vegetable oil in the following solvents: hexane, water, ethanol, and acetone. The last four solutes represent, respectively, a disaccharide, an amino acid (in salt form), a protein, and a lipid, all of which have biological significance.
- Label four test tubes as follows: H (for hexane), W (for water), E (for ethanol) and A (for acetone).
- Half-fill each test tube with the appropriate solvent. Stopper the test tubes immediately because some of the solvents are volatile and have strong odors. AVOID POURING THESE SOLVENTS ON YOUR HANDS.
- Using a spatula, add a pinch (or 3 drops) of any one of the solutes to each of the four test tubes. Ask your teacher to demonstrate a pinch of solute. Be sure to add similar amounts of solutes to the different solvents.
- Stopper each test tube and shake vigorously for 30 seconds, making sure that you hold the stopper in tightly. Record the solubility of each solute as SOLUBLE, SLIGHTLY SOLUBLE, or INSOLUBLE. If two liquids are immiscible (one insoluble in the other), two distinct layers will form. However, when only a few drops of liquid solute are used, small droplets of the solute may adhere to the inside walls of the test tube after shaking and the two layers may not be obvious.
- Repeat the above procedure with each of the other solutes. Wash the test tubes when necessary and be sure to clean your spatula before you sample a new solute.
- Predict what would happen if you add water to an acetone solution of moth flakes. Try it and record your observations?
- Predict what would happen if you add hexane to a solution of water and sugar. Try it and record you observations.
DISPOSAL: All test tubes containing hexane or naphthalene should be emptied into an organic waste container. The other solutions may be poured down the drain.
HAZARDS: Hexane, acetone and ethanol should be used only in a well-ventilated room. These solvents may be poured in the fume hood. Avoid contact of these solvents with the skin.
Experiment 2: THE PERCENT OIL IN PEANUTS
Introduction: The results of the previous experiment showed that hexane is the best solvent for dissolving lipids or vegetable oils. Additional studies shows that hexane is also used as a solvent to extract oil from soybean, corn and other grains. Prior to solvent extraction, the beans are processed into flakes where the oil cells are exposed, allowing the oil to be extracted more easily.
During solvent extraction, hexane is used to wash the flakes. After extraction, the hexane in the extracted oil and the hexane in remaining flakes is evaporated, condensed, and recovered for reuse.
In this experiment we use hexane to extract peanut oil; however we will not recover used hexane.
Keep in mind that peanuts contain oil (similar to the vegetable oil in Part I) and insoluble matter like protein (a polymer synthesized from amino acids).
Get about 50 grams of dry-roasted peanut, peal the outer shell and remove the seeds. Try to have at least 20 grams of shelled peanuts. Use a grinder to grind the peanuts for about 30 seconds.
Transfer the entire crushed peanuts to a glass jar and add 250 mL hexane to that.
Place the lid and shake the jar for 30 seconds.
Filter the mixture to separate the dissolved material from the remaining solids. Collect the hexane-oil mixture in a glass beaker or flask. Place your flask or beaker in a hot water bath to evaporate the hexane and get pure oil. This must be done under the hood or in a well ventilated location.
Separate the outer shell as well as the thin brown layer on the seeds until you get to the white seeds.
Mortar and Pestle may be used for grinding; however, peanuts are slippery and controlling them is hard. It is better to use a small grinder to crush peanuts.
This setup shows the filtration of the hexane peanut mixture.
Materials and Equipment:
Solvents: hexane (C6H14), water (H2O), ethanol (C2H6O), and acetone (C3H6O). (Hexane is a paint diluent, so you may be able to purchase it from paint stores too.)
Solutes: sodium chloride, glycerin, citric acid, naphthalene (moth flakes), sugar, monosodium glutamate, gelatin, and vegetable oil
Monosodium glutamate is used as a flavor enhancer in a variety of foods prepared at home, in restaurants, and by food processors. You can order MSG online from http://www.bulkfoods.com or find it locally in a pharmacy or health food store.
Test tube rack, 13 x 100mm test tubes, rubber stoppers (#00), spatulas
hexane , water , acetone and ethanol .
20 grams shelled, dry-roasted peanuts; Grinder (or Mortar and pestle); Balance
Filter paper and funnel; Hexane
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Following are some sample experiment results. You must do your own experiments and get your own results.
The number of solvents and solutes may be increased or decreased in this experiment, depending on the materials and time available. However, a sufficient number of each should be used so that generalizations can be made about solubility. Solvents can conveniently be dispensed from dropping bottles or plastic wash bottles. Liquid solutes can be dispensed from small plastic dropping bottles (squeeze type). Solid solutes can be dispensed from vials.
Sample Data: Experiment 1
I = Insoluble S = Soluble SS = Slightly Soluble
A solute is considered soluble if it completely dissolves in the solvent. When water is added to an acetone solution of naphthalene, one liquid phase is formed and naphthalene precipitates from the solution. When hexane is added to a solution of sugar in water, two liquid layers form and there is no precipitate. The structures of the solutes are shown below:
Experiment 2: In one experiment, several massed peanuts were mashed in a mortar with a pestle. Hexane was added to the mortar and thoroughly mixed with the mash. The mixture was transferred to a gravity filter and the filtrate was collected in a pre-weighed beaker. The residue in the filter was washed with a few small portions of solvent. The solvent was allowed to evaporate from the beaker and a viscous oil remained. The beaker and oil were massed. The protein/carbohydrate residue was dried and massed.
The following data were collected:
Mass of peanuts = 7.23 g
Mass of empty beaker = 68.11 g
Mass of beaker + oil = 70.80 g
Mass of protein/carbohydrate residue = 4.16 g
Following are some sample calculations:
Mass of oil = 2.69 g
Mass lost = 0.38 g
% oil = 2.69/7.23 x 100% = 37.2% (based on oil recovered)
% oil = 3.07/7.23 x 100% = 42.5% (based on residue)
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Experiment 1 questions:
- Group the eight solutes in categories according to which ones have similar solubility properties. Are there any substances which are difficult to classify?
- Compare these groups you have chosen in terms of the physical properties. Are there many or a few physical properties in common?
- Label the groups of solutes you have formed either as NONPOLAR, SLIGHTLY POLAR, POLAR, or IONIC. Justify your decisions.
- Give explanations for the observations you made in steps 6 & 7.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
This experiment is a modification of an experiment written by Lois Williams, Horace Mann School, Bronx, NY
Submitted by Bob Cairo, Princeton Chemistry Institute, 1988. Modifications by Mark Case, CHEM 6 Team TORCH Binder, 1995.