The most common organic compounds found in living organisms are lipids, carbohydrates, proteins, and nucleic acids. Common foods, which often consist of plant materials or substances derived from animals, are also combinations of these organic compounds. Substance called indicators can be used to test for the presence of organic compounds. An indicator is a substance that changes color in the presence of a particular compound. In this investigation, you will use several indicators to test for the presence of lipids, carbohydrates, and proteins in various foods.
Problem: What are the major types of organic compounds in some common foods?
Pre-lab Discussion:
Substances being tested:
Part A: Testing for Carbohydrates: Monosaccharides
Glucose, commonly called "blood sugar," and fructose, "fruit sugar," are two of the most common monosaccharides. Ribose, an important component of nucleic acids, is also a monosaccharide and will be discussed during our study of DNA and RNA. Monosaccharides can be identified in a substance using an indicator called Benedict's solution. When Benedict's is heated in the presence of a monosaccharide, the color changes from blue to green to yellow to reddish-orange, depending on the amount of monosaccharide present.
Procedure: You can start step 1. and then proceed to another test while the water heats up.
Part B: Testing for Carbohydrates: Polysaccharides
Monosaccharides may join together to form long chains called polysaccharides that may be either straight or branched. Starch is an example of a polysaccharide formed entirely of glucose monosaccharides. Polysaccharides can be tested for using the indicator Lugol's reagent (iodine/potassium iodine). Lugol's will change color from yellow-brown to blue-black-purple in the presence of starch.
Procedure:
Part C: Testing for Lipids
Lipids can be generally categorized into two subgroups: saturated fats and unsaturated fats. In saturated fats, the carbon chains are bonded together with only single covalent bonds and the remaining electrons are bonded to hydrogen. This structure keeps the hydrocarbon tails relatively straight, so they readily align with each other, pack closely together, and thus tend to be solid at room temperature. Saturated fats are most common in animals. Unsaturated fats has double bonds between the carbons and therefore do not have the maximum number of links to hydrogen. These regions of double bonding allow kinks to form in the hydrocarbon tails, keeping them from packing closely together. For this reason, unsaturated fats are usually liquid at room temperature. Unsaturated fats are common in plants. Because fats are nonpolar, we will test for their presence using Sudan IV, a nonpolar dye that will readily mix with lipids but form small bubbles or separate with non-fats. Lipids can also be tested for using the "sack lunch" method: the lipid is rubbed into a brown bag. If a grease spot appears (the brown bag appears translucent), then a lipid is present in the food.
Procedure: Sudan IV
Procedure: Sack lunch
Part D: Testing for Proteins
Proteins are made up of one or more polypeptides, which are linear polymers of monomers called amino acids. Amino acids derive their name from the amino group and the carboxyl group (which is acidic). Polypeptides are formed when amino acids are joined together by peptide bonds between the amino group of one amino acid and the carboxyl group of another amino acid. Proteins can be tested for using Biuret's reagent, which reacts with the peptide bond between amino acids in the polypeptide. Biuret's reagent turns from blue to purple-violet if peptides bonds are present.
Procedure:
An indicator used to detect an acid or base is a substance that changes color in the presence of acids or bases. Examples of indicators include litmus paper, phenolphthalein, and universal indicator solution.
Litmus is an example of a compound that can reversibly change color depending on conditions such as pH. It is commonly used as a pH indicator to visually determine the acidity or basicity of a solution.
It is litmus, an extract from several different species of lichens, that is used as an indicator between acid and alkaline conditions.
A universal indicator is commonly used to detect the presence of an acid or alkali. It changes color based on the acidity or alkalinity of a solution, helping to identify whether a substance is acidic, neutral, or alkaline.
No, sodium bicarbonate is not an indicator. It is a chemical compound commonly used for its buffering and antacid properties. Indicators are substances that change color in response to changes in pH levels.
No, bromthymol blue is not a living organism. It is a chemical compound commonly used as a pH indicator in laboratories to detect changes in acidity or alkalinity in a solution.
Compound eyes detect motion, and simple eyes detect light. or The compound eyes are used to "see". The simple eyes are used to detect light intensity.
Vitamin C - iodine solution is the indicator commonly used to detect the presence of vitamin C due to the color change reaction that occurs.
An indicator used to detect an acid or base is a substance that changes color in the presence of acids or bases. Examples of indicators include litmus paper, phenolphthalein, and universal indicator solution.
Andrade's indicator is typically green in color. It is used in organic chemistry to test for the presence of unsaturation in a compound by changing color when it reacts with the compound in question.
To detect a water meter leak using the water meter leak indicator, you can observe the leak indicator dial on the water meter. If the dial is moving when no water is being used in the house, it indicates a leak in the water system.
Litmus is an example of a compound that can reversibly change color depending on conditions such as pH. It is commonly used as a pH indicator to visually determine the acidity or basicity of a solution.
This substance is called indicator.
It is litmus, an extract from several different species of lichens, that is used as an indicator between acid and alkaline conditions.
Phenolphthalein is an organic compound (C20H14O4) used as an acid-base indicator. The compound is colorless in acidic solution and pinkish in basic
Diphenylamine is considered an internal indicator because it changes color in the presence of nitrates by forming a blue complex. This color change is used to detect the presence of nitrates in solutions without the need for an external indicator.
A universal indicator is commonly used to detect the presence of an acid or alkali. It changes color based on the acidity or alkalinity of a solution, helping to identify whether a substance is acidic, neutral, or alkaline.