Fuels and other compound: MCQ 4

Preparation of Ethyne Experiment

• Calcium dicarbide is a grey solid that cannot be obtained in a pure state.
• Ethyne is obtained from calcium dicarbide and is usually contaminated with gases like hydrogen sulphide and ammonia.
• These impurities are removed by bubbling the ethyne produced through acidified copper sulphate.
• Calcium dicarbide is extremely flammable and should be used in small amounts to avoid explosion risks.

Aromatic Compounds

• Aromatic compounds have a benzene ring in their structure, which contains six carbons in a ring.
• The carbon bonds in the benzene ring are intermediate between C-C and C=C due to delocalised pi bonding.
• Aromatic compounds are classified as unsaturated.
• They are non-polar, insoluble in water, and are good non-polar solvents.

Properties of Aromatic Compounds

• Physical State: low Mr → liquids at room temp, high Mr → solids at room temp
• Solubility: non-polar, insoluble in water, good non-polar solvents
• Must-known structures: benzene, methylbenzene, ethylbenzene
• Benzene is carcinogenic, while some of its derivatives are not (e.g., aspirin, phenolphthalein).

Fuels and Other Compounds

Chloroalkanes

• Chloroalkanes are alkanes where at least one hydrogen atom has been replaced by a chlorine atom.
• They are saturated compounds, usually liquids, and rarely found in nature.
• Although the C-Cl bond is polar, it is not polar enough to allow chloroalkanes to dissolve in water.
• They are classified as non-polar because they are soluble in cyclohexane.
• Uses of chloroalkanes include anaesthetics (chloroform) and solvents.

Alcohols

• All alcohols contain a hydroxyl (OH) group, and their names end in "ol".
• There are three types of alcohols: primary, secondary, and tertiary.
• Primary alcohols undergo oxidation reactions to form aldehydes, while secondary alcohols undergo oxidation reactions to form ketones.
• Physical State & Properties of Alcohols: similar physical properties (same physical state, same boiling point) when comparing propane and ethanol.

Intermolecular Forces

• Hydrogen bonding occurs in alcohols because hydrogen is bonded to oxygen, resulting in a strongly polar OH bond.
• Ethanol is soluble in water because H₂O is a polar solvent, and ethanol and water are completely miscible due to the formation of hydrogen bonds.

Production of Ethanol

• Ethanol can be produced through hydration of ethene or fermentation of sugars in fruits and vegetables.
• Fermentation is an anaerobic process during which enzymes found in yeast break down sugars into alcohol.
• Ethanol has various everyday uses, including as a polar solvent in paints, aftershaves, and perfumes, and as a fuel.

Methanol

• Methanol is a poisonous alcohol and usually contains a purple dye when added to fuels such as methylated spirits to prevent consumption by people.
• Methanol used in this way is said to be a denaturing agent.

Planar and Tetrahedral Organic Compounds

• These compounds have atoms on the same plane (i.e., all atoms are "flat") and involve double or triple bonds.
• Examples include ethene, alkenes, alkynes, aldehydes, ketones, carboxylic acids, esters, and aromatic compounds.