Carbon dioxide has two double covalent bonds. Its electron-dot structure is O=C=O, with carbon sharing two pairs of electrons with each oxygen atom; each oxygen also has two lone pairs.
A sulphur molecule is S₈. The eight sulphur atoms are joined in a ring by single covalent bonds; each sulphur shares one electron with each of two neighbouring sulphur atoms and has two lone pairs remaining.
Three structural isomers can be drawn for pentane: n-pentane, isopentane (2-methylbutane) and neopentane (2,2-dimethylpropane).
The two properties are catenation and tetravalency. Catenation lets carbon form long chains, branched chains and rings with itself. Tetravalency lets carbon form four covalent bonds with carbon and other elements.
Cyclopentane has the formula C₅H₁₀. It is a ring of five carbon atoms joined by single bonds, with each carbon also bonded to two hydrogen atoms, so every carbon completes four covalent bonds.
(i) Ethanoic acid: CH₃–COOH.
(ii) Bromopentane: CH₃–CH₂–CH₂–CH₂–CH₂–Br (one possible structure).
(iii) Butanone: CH₃–CO–CH₂–CH₃.
(iv) Hexanal: CH₃–CH₂–CH₂–CH₂–CH₂–CHO.
Yes, structural isomers are possible for bromopentane because bromine can be attached at different carbon positions in the pentane chain.
(i) Bromoethane.
(ii) Methanal.
(iii) Hex-1-yne.
Ethanol is converted to ethanoic acid by adding oxygen/removing hydrogen. Since oxidation is gain of oxygen or loss of hydrogen, this conversion is an oxidation reaction.
Ethyne burns completely in oxygen and produces a very hot flame suitable for welding. Air contains only about 21% oxygen, so ethyne burns incompletely in air and gives a sooty, lower-temperature flame.
Add sodium carbonate or sodium hydrogencarbonate to each liquid. A carboxylic acid reacts with brisk effervescence of CO₂, while an alcohol does not. Ethanoic acid, for example, reacts with NaHCO₃ to give CO₂.
Oxidising agents are substances that add oxygen to another substance or remove hydrogen from it. Examples include alkaline potassium permanganate and acidified potassium dichromate.
No. Detergents form lather in both hard and soft water because they do not form insoluble scum with calcium and magnesium ions. Soap, not detergent, is useful for checking hardness by lather formation.
Soap forms micelles around oily dirt. Agitation helps the micelles detach the dirt from the cloth and disperse it in water, so the dirt can be washed away.
- a. 6 covalent bonds.
- b. 7 covalent bonds.
- c. 8 covalent bonds.
- d. 9 covalent bonds.
Ethane has one C–C single bond and six C–H bonds, making 7 covalent bonds in total.
(b) 7 covalent bonds.
- a. carboxylic acid.
- b. aldehyde.
- c. ketone.
- d. alcohol.
The suffix -one indicates a ketone functional group.
(c) ketone.
- a. the food is not cooked completely.
- b. the fuel is not burning completely.
- c. the fuel is wet.
- d. the fuel is burning completely.
A yellow sooty flame and black deposit are signs of incomplete combustion.
(b) the fuel is not burning completely.
In a covalent bond, atoms share pairs of electrons to complete their outer shells. In CH₃Cl, carbon has four valence electrons and shares one electron each with three hydrogen atoms and one chlorine atom. Thus carbon forms four single covalent bonds; hydrogen attains a duplet and chlorine completes its octet.
(a) Ethanoic acid: CH₃–C(=O)–OH, with two lone pairs on each oxygen.
(b) H₂S: H–S–H, with two lone pairs on sulphur.
(c) Propanone: CH₃–C(=O)–CH₃, with two lone pairs on oxygen.
(d) F₂: F–F, with each fluorine having three lone pairs.
A homologous series is a family of organic compounds with the same functional group and similar chemical properties, in which successive members differ by a –CH₂– unit. Example: alcohols, CH₃OH, C₂H₅OH, C₃H₇OH, etc., all contain the –OH group.
Physically, ethanol has a pleasant smell and burns with a blue flame, while ethanoic acid has a vinegar-like smell and is sour. Chemically, ethanoic acid reacts with sodium carbonate or sodium hydrogencarbonate to release CO₂, while ethanol does not. Ethanoic acid also turns blue litmus red; ethanol is neutral.
Soap molecules have hydrophilic ionic heads and hydrophobic hydrocarbon tails. In water, the tails avoid water and cluster inside while the heads face water, forming micelles. In ethanol, the hydrocarbon tails are also soluble, so micelles are not formed in the same way.
Carbon compounds generally burn in air to form CO₂ and water, releasing a large amount of heat and light. They have good calorific values and are available in useful forms such as coal, petroleum products, natural gas and biomass.
Hard water contains calcium and magnesium ions. These ions react with soap to form insoluble calcium and magnesium salts of fatty acids, which appear as scum and reduce lather formation.
Soap solution is basic. It turns red litmus blue, while blue litmus remains blue.
Hydrogenation is the addition of hydrogen to unsaturated hydrocarbons in the presence of a catalyst such as nickel or palladium. Industrially it is used to convert vegetable oils into vegetable ghee or vanaspati.
Unsaturated hydrocarbons undergo addition reactions. Therefore C₃H₆ and C₂H₂ undergo addition reactions; C₂H₆, C₃H₈ and CH₄ are saturated and usually do not.
Add bromine water or alkaline potassium permanganate solution. Unsaturated hydrocarbons decolourise bromine water or KMnO₄ because they undergo addition/oxidation reactions; saturated hydrocarbons do not decolourise them under ordinary conditions.
A soap molecule has a hydrophilic ionic head and a hydrophobic hydrocarbon tail. In water, the hydrophobic tails attach to oily dirt while the hydrophilic heads remain in water. Many soap molecules surround a dirt particle to form a micelle, with the oil trapped in the centre. Agitation loosens these micelles from the cloth, and they remain suspended in water and are washed away.