33: Important Organic Substances Flashcards
What is the definition of drugs?
Drugs are substances which alter physiological and/or mental functioning. They bind to certain receptors in our body to trigger corresponding functions.
What is the active ingredient of aspirin?
Acetylsalicylic acid
List the functional groups acetylsalicylic acid has.
Carboxyl group and ester functional group.
Explain why taking in excessive aspirin tablets may cause stomach pain and stomach ulcer.
Aspirin tablets contain acetylsalicylic acid. Inside the stomach, the environment is acidic and the rate of dissociation of acid molecules is low. The mucus lining of the stomach allows the passage of neutrally charger molecules, and the acid molecules are able to pass the lining. However, the acid molecules undergo dissociation in the neutral environment pass the mucus lining, releasing hydrogen ions which can damage the tissues.
Compare the effects of using sodium hydroxide, sodium carbonate, and sodium hydrogencarbonate to make soluble aspirin.
All three substances can make soluble aspirin. However, sodium hydroxide and sodium carbonate are stronger bases than sodium hydrogencarbonate, which may hydrolyse the ester bond in aspirin molecules. Therefore, sodium hydrogencarbonate is usually preferred to reduce chance of hydrolysis of the molecule.
What is the difference between soapy detergent and soapless detergent?
Soapy detergents are detergents with carboxylate ions as the ionic head, while soapless detergents are detergents with any other ionic head.
What are triglycerides?
Triglycerides are triesters formed by linking one glycerol molecule with three fatty acid molecules with ester bonds.
What are the differences between the chemical composition of animal fat and plant oil?
Animal fat is saturated and the fatty acid tails have a zig-zag shape. Plant oil is unsaturated, consisting of carbon-carbon double bonds within their fatty acid tails, thus the tails are twisted.
Explain the difference in the physical states of animal fat and plant oil at room temperature.
Animal fat is usually solid at room temperature while plant oil is usually liquid. Since plant oil consists of carbon-carbon double bonds within their fatty acid tails, the tails are twisted and packed in an irregular form, unlike the regular zig-zag form of animal fats. This means that molecules of plant oil cannot be packed close together, and they experience weaker van der Waals’ forces among their molecules compared to animal fat. Thus, plant oil has a lower melting point than animal fat, and remains as a liquid in room temperature while animal fat is a solid.
Explain the number of carbon atoms on fatty acid tails on triglycerides used to make soap.
They have usually 16-20 carbon atoms. If there are too few carbon atoms, the carboxylic acid becomes too short and soluble in water. If there are too many carbon atoms, the carboxylic acid becomes too long and completely insoluble in water. The narrow range of lengths of carbon chain makes sure that the soap can mix with both oil and water.
What is the definition of salting-out?
Salting-out is a process in which the solubility of a dissolved soap molecule is reduced by adding concentrated sodium chloride solution to the mixture. The soap then separates from the mixture and floats on the surface.
Explain why adding concentrated sodium chloride solution lowers the solubility of soap molecules in water.
Sodium ions and chloride ions are added, and they have a much higher charge-to-size ratio compared to soap molecules. They experience very strong attraction with water molecules and are much more soluble in water than the soap molecules. Therefore, the water molecules tend to surround the ions, leaving the soap molecules to cluster as a solid precipitate.
What are the properties of the two different parts of a soap molecule?
Long hydrocarbon tail which is soluble in oil and hydrophobic, and an anionic head which is soluble in water / hydrophilic.
What are the two properties of soap contributing to its cleansing action?
Its wetting property and cleansing property.
How does soap exhibit wetting property on a piece of fabric?
Water usually beads up on a piece of fabric due to its high surface tension. However, with the addition of soap molecules, they tend to stay at the surface with hydrophobic hydrocarbon ends sticking outwards. This disrupts the cohesion between water molecules and reduces the surface tension of water. Water is allowed to spread and cover a wider surface of the fabric.
How does soap exhibit emulsifying property?
Oil and water usually do not mix, and separate after standing even after shaking. When soap is added to an oil and water mixture and shaken, fine oil droplets form. Each oil droplet is surrounded by soap molecules which the anionic heads in water. The oil droplets cannot come together again due to the repulsion between the charged anionic heads. This allows the oil droplets to stand after a long time.
How do the properties of soap contribute to its cleansing action?
When soap solution is added to a fabric with grease and dirt, the hydrocarbon “tails” of the soap molecules dissolve in the grease, leaving the anionic “heads” sticking out. The surrounding water than attract the anionic heads and lift the grease off the surface.
The grease breaks up into tiny droplets when stirred, and it is then surrounded by soap molecules with the anionic “heads” pointing outwards. The droplets cannot come close together due to repulsion between the anionic “heads” of the soap molecules. This enables grease molecules to be broken up and rinsed away.
List two scenarios which soapy detergents are not effective.
In hard water containing calcium ions or magnesium ions, and in acidic medium.
Why do soapy detergents lose its cleansing property in hard water?
In hard water, soapy detergents react with calcium ions and magnesium ions to form water-insoluble precipitates. This causes soap molecules to lose its wetting and emulsifying property and hinder the cleansing process.
Why do soapy detergents lose its cleansing property in acidic medium?
In acidic medium, soap molecules remain as acid molecules since the dissociation is suppressed by the acidic medium. This causes the soap molecules to be less soluble in water, thus reducing its cleansing property.
List two common anionic head of soapless detergents and their chemical structures.
Sulphate group, sulphonate group
What is the definition of condensation polymers?
A condensation polymer is formed when many monomer molecules join together via condensation reactions, with the elimination of simple molecules such as water.
Name two kinds of condensation polymers.
Polyesters, polyamides
What is the definition of polyesters?
Polyesters are condensation polymers in which the monomer units are joined together by ester linkages.
