Class 10 Chemical properties of carbon compounds, Some important carbon compounds, soaps and detergents

### Topics to be covered

=> Chemical properties of carbon compounds
=> Oxidation
=> Addition reaction
=> Substitution reaction
=> Some important carbon compounds- ethanol and ethanoic acid
=> Soaps and detergents

### CHEMICAL PROPERTIES OF CARBON COMPOUNDS

color{green}(•) Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of heat and light.
color{green}(•) Most carbon compounds also release a large amount of heat and light on burning. These are the oxidation reactions . For eg:
(i) color{red}( C+ O_2 → CO_2 + " heat and light")

(ii) color{red}(CH_4 + O_2 → CO_2 + H_2O + "Heat and light")

(iii) color{red}(CH_3CH_2OH + O_2 → CO_2 + H_2O + "Heat and light")

color{green}("𝐒𝐀𝐓𝐔𝐑𝐀𝐓𝐄𝐃 𝐀𝐍𝐃 𝐔𝐍𝐒𝐀𝐓𝐔𝐑𝐀𝐓𝐄𝐃 𝐂𝐎𝐌𝐏𝐎𝐔𝐍𝐃𝐒")

color{green}(•) Saturated hydrocarbons will generally give a clean flame.

color{green}(•) Unsaturated carbon compounds will give a yellow flame with lots of black smoke that results in a sooty deposit on the metal plate .

color{green}(•) If the supply of air is limited it results in incomplete combustion of even saturated hydrocarbons giving a sooty flame.

color{green}(•) The gas/kerosene stove used at home has inlets for air so that a sufficiently oxygen-rich mixture is burnt to give a clean blue flame.

color{red}("𝐉𝐔𝐒𝐓 𝐅𝐎𝐑 𝐂𝐔𝐑𝐈𝐎𝐔𝐒")

If you observe the bottoms of cooking vessels getting blackened, it means that the air holes are blocked and fuel is getting wasted. Fuels such as coal and petroleum have some amount of nitrogen and sulphur in them. Their combustion results in the formation of oxides of sulphur and nitrogen which are major pollutants in the environment.

### Oxidation

The substances that are capable of adding oxygen to others are known as oxidising agents. For eg: alkaline potassium permanganate or acidified potassium dichromate are oxidising alcohols to acids, that is, adding oxygen to the starting material. Hence they are known as oxidising agents.

color{red}(CH_3 - CH_2OH underset("Or acidified " K_2Cr_2O_7+"Heat") overset("Alkaline " KMnO_4 + " Heat")→ CH_3COOH)

Unsaturated hydrocarbons gets converted to saturated hydrocarbons by the addition of hydrogen in the presence of catalysts such as palladium or nickel.

𝐂𝐚𝐭𝐚𝐥𝐲𝐬𝐭𝐬 𝐚𝐫𝐞 𝐬𝐮𝐛𝐬𝐭𝐚𝐧𝐜𝐞𝐬 𝐭𝐡𝐚𝐭 𝐜𝐚𝐮𝐬𝐞 𝐚 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧 𝐭𝐨 𝐨𝐜𝐜𝐮𝐫 𝐨𝐫 𝐩𝐫𝐨𝐜𝐞𝐞𝐝 𝐚𝐭 𝐚 𝐝𝐢𝐟𝐟𝐞𝐫𝐞𝐧𝐭 𝐫𝐚𝐭𝐞 𝐰𝐢𝐭𝐡𝐨𝐮𝐭 𝐭𝐡𝐞 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧 𝐢𝐭𝐬𝐞𝐥𝐟 𝐛𝐞𝐢𝐧𝐠 𝐚𝐟𝐟𝐞𝐜𝐭𝐞𝐝.

color{green}("𝐔𝐒𝐄 𝐎𝐅 𝐀𝐃𝐃𝐈𝐓𝐈𝐎𝐍 𝐑𝐄𝐀𝐂𝐓𝐈𝐎𝐍")

This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains.

Animal fats generally contain saturated fatty acids and are said to be harmful for health. Therefore oils containing unsaturated fatty acids should be chosen for cooking.

### Substitution Reaction

color{green}(•) Saturated hydrocarbons are fairly unreactive and are inert in the presence of most reagents.

color{green}(•) However, in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction in which chlorine can replace the hydrogen atoms one by one. It is called a substitution reaction .

color{green}(•) A reaction in which an atom or group of atoms replaces another atom or group of atoms is called color{red}("𝐬𝐮𝐛𝐬𝐭𝐢𝐭𝐮𝐭𝐢𝐨𝐧 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧")

color{green}(•) A number of products are usually formed with the higher homologues of alkanes.

color{red}(CH_4+ Cl_2 → CH_3Cl + HCl "(in the presence of sunlight)")

### SOME IMPORTANT CARBON COMPOUNDS – ETHANOL AND ETHANOIC ACID

color{green}("𝟏 𝐏𝐫𝐨𝐩𝐞𝐫𝐭𝐢𝐞𝐬 𝐨𝐟 𝐄𝐭𝐡𝐚𝐧𝐨𝐥 :")

color{green}(•) Ethanol is a liquid at room temperature .

color{green}(•) Ethanol is commonly called alcohol and is the active ingredient of all alcoholic drinks.

color{green}(•)It is a good solvent therefore it is used in medicines such as tincture iodine, cough syrups, and many tonics.

color{green}(•) Ethanol is also soluble in water in all proportions.

color{green}(•) Consumption of small quantities of dilute ethanol causes drunkenness.

color{green}(•) Intake of even a small quantity of pure ethanol (called absolute alcohol) can be lethal.

color{green}(•) Long-term consumption of alcohol leads to many health problems.

color{green}("𝐑𝐞𝐚𝐜𝐭𝐢𝐨𝐧𝐬 𝐨𝐟 𝐄𝐭𝐡𝐚𝐧𝐨𝐥 :")

(i) Reaction with sodium color{red}(2Na+ 2CH_3CH_2OH → underset("(Sodium ethoxide)")(2CH_3 CH_2O^(-) Na^(+)) + H_2)

Alcohols react with sodium leading to the evolution of hydrogen. With ethanol, the other product is sodium ethoxide.

(ii) Reaction to give unsaturated hydrocarbon:

Heating ethanol at 443 K with excess concentrated sulphuric acid (act as a dehydrating agent which removes water from ethanol )results in the dehydration of ethanol to give ethene .

color{red}(CH_3 + CH_2OH underset(H_2SO_4) overset(" Hot cone") → CH_2 = CH_2 + H_2O)

color{green}("𝟐 𝐏𝐫𝐨𝐩𝐞𝐫𝐭𝐢𝐞𝐬 𝐨𝐟 𝐄𝐭𝐡𝐚𝐧𝐨𝐢𝐜 𝐀𝐜𝐢𝐝")

color{green}(•) Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids.

color{green}(•) 5-8% solution of acetic acid in water is called vinegar and is widely used as a preservative in pickles.

color{green}(•) The melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid.

The group of organic compounds called carboxylic acids are obviously characterised by a special acidity. However, unlike mineral acids like color{red}(HCl), which are completely ionised, carboxylic acids are weak acids.

color{green}("𝐑𝐞𝐚𝐜𝐭𝐢𝐨𝐧𝐬 𝐨𝐟 𝐞𝐭𝐡𝐚𝐧𝐨𝐢𝐜 𝐚𝐜𝐢𝐝:")

color{red}("(𝐢) 𝐄𝐬𝐭𝐞𝐫𝐢𝐟𝐢𝐜𝐚𝐭𝐢𝐨𝐧 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧:") Esters are most commonly formed by reaction of an acid and an alcohol. Ethanoic acid on reaction with ethanol in the presence of an acid catalyst yields ester .

color{red}(underset("(Ethanoic acid)")(CH_3- COOH) + underset("(Ethanol)") (CH_3 - CH_2 OH) overset("Acid")→ underset("(Ester)")(CH_3 - underset(underset(O)(||))C - O - CH_2 - CH_3))

color{red}(" (i) 𝐏𝐫𝐨𝐩𝐞𝐫𝐭𝐢𝐞𝐬 𝐨𝐟 𝐞𝐬𝐭𝐞𝐫𝐬 :")

color{green}(•) Esters are sweet-smelling substances.

color{green}(•) They are used in making perfumes and as flavouring agents.

color{green}(•) On treating with sodium hydroxide, which is an alkali, the ester is converted back to alcohol and sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.

color{green}(" 𝐑𝐞𝐚𝐜𝐭𝐢𝐨𝐧 𝐰𝐢𝐭𝐡 𝐚 𝐛𝐚𝐬𝐞:")

Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to give a salt (sodium ethanoate or commonly called sodium acetate) and water.

color{red}(NaOH + CH_3COOH → CH_3 COONa + H_2O)

color{red}("(𝐢𝐢𝐢) 𝐑𝐞𝐚𝐜𝐭𝐢𝐨𝐧 𝐰𝐢𝐭𝐡 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞𝐬 𝐚𝐧𝐝 𝐡𝐲𝐝𝐫𝐨𝐠𝐞𝐧𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞𝐬 :") Ethanoic acid reacts with carbonates and hydrogencarbonates to give rise to a salt, carbon dioxide and water. The salt produced is commonly called sodium acetate.

color{red}(2CH_3COOH + Na_2CO_3 → 2CH_3 COONa + H_2O + CO_2)

color{red}(CH_3COOH + NaHCO_3 → CH_3COONa + H_2O + CO_2)

### SOAPS AND DETERGENTS

color{green}(•) Most dirt is oily in nature and we know that oil does not dissolve in water.

color{green}(•) The molecules of soap are sodium or potassium salts of long-chain carboxylic acids.

color{green}(•) The ionic-end of soap dissolves in water while the carbon chain dissolves in oil. The soap molecules, thus form structures called micelles where one end of the molecules is towards the oil droplet while the ionic-end faces outside.

color{green}(•) This forms an emulsion in water. The soap micelle thus helps in dissolving the dirt in water and we can wash our clothes clean (Fig. 4.13).

color{green}(•) Sometimes foam is formed with difficulty and an insoluble substance (scum) remains after washing with water. This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water. This problem is overcome by detergents that act as cleansing agents.

color{green}(•) Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water.

color{green}("𝐔𝐒𝐄 𝐎𝐅 𝐃𝐄𝐓𝐄𝐑𝐆𝐄𝐍𝐓𝐒")

Detergents are usually used to make shampoos and products for cleaning clothes.