Chemical Properties of Carbon Compounds

Combustion is the process of burning carbon compounds in the presence of oxygen, producing carbon dioxide, water vapour, heat, and light.

1. C + O₂ → CO₂ + heat + light 

   (Carbon)

2. CH₄ + 2O₂ → CO₂ + 2H₂O + heat + light

  (Methane)

3. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat + light 

  (Ethanol)

Observations:

• Saturated hydrocarbons burn with a clean blue flame (complete combustion).
• Unsaturated hydrocarbons burn with a yellow, sooty flame due to excess carbon and incomplete combustion.
• Incomplete combustion produces carbon monoxide (CO), a poisonous gas that binds with haemoglobin to form carboxyhaemoglobin, reducing oxygen supply to body tissues and potentially causing death.

1. Aim: To observe the flame characteristics during the combustion of saturated and unsaturated carbon compounds and detect soot formation.

2. Requirements: Bunsen burner, copper gauze, metal plate, ethanol (saturated compound), acetic acid, and naphthalene (unsaturated compound).

3. Procedure

1. Place 3–4 drops (or a pinch) of one compound (e.g., ethanol) on clean copper gauze.
2. Hold the gauze in the blue flame of a Bunsen burner.
3. Observe whether the flame is blue or yellow and whether smoke or soot is formed.
4. Hold a metal plate above the flame and check for black soot deposits.
5. Repeat the same with acetic acid and naphthalene.
6. Adjust the air hole of the burner to observe changes in flame colour.

4. Observations

• Ethanol burns with a clean blue flame (complete combustion, no soot).
• Naphthalene burns with a yellow sooty flame (incomplete combustion, black soot forms).
• Limited oxygen supply (closed air hole) gives a yellow sooty flame, even with ethanol.
• An open air hole gives a blue flame with the proper oxygen mix.

5. Conclusion

• Saturated compounds (like ethanol) burn cleanly with a blue flame.
• Unsaturated compounds (like naphthalene) burn with a yellow flame and produce soot due to higher carbon content.
• The flame colour and soot formation indicate the degree of saturation and availability of oxygen.

Oxidation involves the addition of oxygen or removal of hydrogen from a molecule.  It's often used to convert one functional group into another.

• Combustion is a complete oxidation reaction.
• Not all oxidation reactions are combustion.
• Oxidising agents like potassium permanganate (KMnO₄) and potassium dichromate (K₂Cr₂O₇) are used to carry out controlled oxidation.
• Oxidation helps in converting alcohols to acids or aldehydes.

Example:

\[CH_3CH_2OH\xrightarrow{[O],KMnO_4}CH_3COOH\]

1.Aim: To demonstrate the oxidation of ethanol using an oxidising agent (potassium permanganate) and observe the formation of ethanoic acid.

2. Requirements: Test tube, bunsen burner, measuring cylinder, dropper, ethanol, dilute sodium carbonate solution, and dilute potassium permanganate solution

3. Procedure

• Take 2–3 ml of ethanol in a test tube.
• Add 5 ml of dilute sodium carbonate solution.
• Warm the mixture gently using a Bunsen burner.
• Add dilute potassium permanganate solution drop by drop while stirring.
• Observe the change in the pink colour of potassium permanganate during the reaction.

4. Observation

• The pink colour disappears at first, showing that KMnO₄ is reacting.
• After some time, the pink colour remains, indicating excess KMnO₄ and completion of ethanol oxidation.

5. Conclusion

Ethanol is oxidised to ethanoic acid by potassium permanganate. The disappearance of the pink colour indicates that oxidation is occurring. This experiment demonstrates how oxidising agents like KMnO₄ convert alcohols into acids.

Chemical Equation:

\[\mathrm{CH_3CH_2OH}\xrightarrow{[O],\text{alkaline KMnO.}}\mathrm{CH_3COOH}\]

(Ethanol to Ethanoic Acid)

An addition reaction occurs when unsaturated compounds (with double or triple bonds) react with another molecule (like H₂, Br₂, or I₂), forming a saturated compound.

Example:

Ethene + H₂ → Ethane

\[CH_2=CH_2+H_2\xrightarrow{Ni/Pt}CH_3CH_3\]

Testing for Unsaturation: Adding bromine water or iodine solution to oils

• Disappearance of colour indicates an unsaturated compound.
• No colour change means the compound is saturated.

Hydrogenation of Oils:

• Vegetable oils contain unsaturated fatty acids.
• In the presence of a nickel catalyst, hydrogen is added, forming saturated fats (Vanaspati ghee).
• Though unsaturated fats are healthier, saturated fats have a longer shelf life.

Fatty Acid Comparison:

1. Aim: To test for the presence of double bonds (C=C) in oils using iodine or bromine water and to understand addition reactions in unsaturated compounds.

2. Requirements: Test tubes, droppers, tincture iodine or bromine water, liquefied Vanaspati ghee, and vegetable oils (peanut, sunflower, safflower, olive, etc.)

3. Procedure

• Take 4 ml of a vegetable oil in a test tube.
• Add 4 drops of tincture iodine or bromine water to the oil.
• Shake the test tube gently.
• Observe whether the original colour of iodine or bromine disappears.
• Repeat the same steps with Vanaspati ghee and other oils.

4. Observations

• The colour of iodine/bromine disappears with vegetable oils.
• The colour remains unchanged with Vanaspati ghee.

5. Conclusion

• Vegetable oils are unsaturated; they contain double bonds and undergo addition reactions, causing the decolourisation.
• Vanaspati ghee is saturated, so no reaction occurs, and the colour stays.
• This confirms that addition reactions occur in unsaturated compounds and can be used to test for C=C double bonds.

A substitution reaction is one where an atom or group in a molecule is replaced by another atom or group, typically seen in saturated hydrocarbons (alkanes).

Example: Chlorination of Methane

In the presence of sunlight, chlorine replaces hydrogen atoms:

\[\mathrm{CH}_{4}\quad+\mathrm{Cl}_{2}\xrightarrow{\mathrm{Sunlight}}\quad\mathrm{CH}_{3}-\mathrm{Cl}+\mathrm{HCl}\]

\[\mathrm{CH_3Cl~+~Cl_2~\xrightarrow{Sunlight}~CH_2Cl_2~+HCl}\]

\[\mathrm{CH}_2\mathrm{Cl}_2+\mathrm{Cl}_2\xrightarrow{\mathrm{Sunlight}}\mathrm{CHCl}_3+\mathrm{HCl}\]

\[\mathrm{CHCl}_{3}+\mathrm{Cl}_{2}\xrightarrow{\mathrm{Sunlight}}\mathrm{CCl}_{4}+\mathrm{HCl}\]

Key Characteristics:

• Sunlight is required for the reaction to proceed.
• It proceeds step-by-step, replacing one hydrogen at a time.
• A series of chlorinated products can form, especially in higher alkanes.