An addition reaction is a reaction in which new atoms are added to the organic compound by converting carbon-carbon double covalent bonds to carbon-carbon single covalent bonds.
Category: Pure Chemistry
What is a homologous series?
A homologous series is a family of organic compounds with:
– same functional group
– same general formula
– similar chemical properties
– gradual change in physical properties
Examples of homologous series:
– Alkanes
– Alkenes
– Alcohols
Describe the structure of metals and metallic bonds.
The structure of metal consists of positive metal ions, arranged in a regular pattern, floating in a sea of delocalized electrons.
Metal atoms have the tendency to lose their valence electrons to form positive ions.
These valence electrons become delocalized and form a ‘sea of mobile electrons’ around the positive ions.
The strong electrostatic force of attraction between the positive metal ions and delocalized electrons form strong metallic bonds.
The layers of metal ions can slide over one another when sufficient force is applied.
In paper chromatography, the start line is drawn with a pencil rather than a pen. Explain the reason for this.
Pen ink consists of a mixture of dyes that can dissolve in the solvent and contaminate the chromatogram.
Pencil lead is usually made of insoluble graphite, which made it suitable for drawing the start line in paper chromatography.
Describe the test for sulfur dioxide gas.
Bubble the gas into acidified potassium manganate (VII) solution.
KMnO4 solution changes color from purple to colorless in the presence of sulfur dioxide gas.
What are drying agents and what are the common drying agents?
Drying agents are substances that can be used to obtain a dry sample of a gas by removing its moisture content.
Examples:
* Anhydrous calcium chloride (for any gas except ammonia)
Ammonia will react with calcium chloride.
4NH3 (g) + CaCl2 (s) –> CaCl2.4NH3 (s)
* Concentrated sulfuric acid (for any gas except alkaline gases such as ammonia)
* Calcium oxide
(for any gas except acidic gases such as CO2 and SO2)
Define Kinetic Particle Theory.
Kinetic Particle Theory states that all matter is made up of tiny, discrete particles that are in constant, random motion.
In paper chromatography, why must the start line be above the solvent level?
The start line above the solvent level allows the solvent to move past the start line, carrying the dissolved samples along with it.
With the start line below the solvent level, the samples on the start line will dissolve in the solvent right at the beginning, contaminating the whole solvent, causing the chromatogram to be inaccurate.
Explain the importance of the measurement of the purity of substances that we use in foodstuffs and drugs.
For substances used in preparing food and drugs, it is important to ensure that only permitted substances are being used.
If a substance is impure, and laced with some other substances, these unapproved impurities might not be safe for human consumption, and lead to undesirable effects on human health.
What are the 2 methods to determine the purity of a substance?
To determine the purity of a substance, test its melting point or boiling point.
If it melts or boils at a fixed temperature, it is a pure substance.
Another method is to carry out a chromatography of the substance.
If it separates out into only one spot on the chromatogram, it is a pure substance.