CIE iGCSE Co-ordinated Sciences-C11.6 Alcohols- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C11.6 Alcohols – Study Notes
CIE iGCSE Co-ordinated Sciences-C11.6 Alcohols – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe the complete combustion of ethanol
- State the uses of ethanol as:
(a) a solvent
(b) a fuel
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Complete Combustion of Ethanol
Combustion means the burning of a substance in oxygen. Complete combustion occurs when a fuel burns in a plentiful supply of oxygen, producing carbon dioxide (CO₂) and water (H₂O).
Chemical Formula of Ethanol:
\(\mathrm{C_2H_5OH}\)
Word Equation:
Ethanol + Oxygen → Carbon dioxide + Water
Chemical Equation:
\(\mathrm{C_2H_5OH + 3O_2 → 2CO_2 + 3H_2O}\)
Balanced Equation Check:
- Carbon atoms: 2 on both sides
- Hydrogen atoms: 6 on both sides
- Oxygen atoms: 7 on both sides
Explanation:
- In complete combustion, ethanol reacts fully with oxygen.
- All carbon in ethanol is converted to carbon dioxide (CO₂).
- All hydrogen in ethanol is converted to water (H₂O).
- Energy is released in the form of heat and light.
Observation:
- Ethanol burns with a clean, blue flame (indicating complete combustion).
Energy Change:
- Combustion of ethanol is an exothermic reaction.
- This means it releases heat energy.
- Ethanol is therefore used as a biofuel and as an additive to petrol to make it burn more cleanly.
Key Idea: During complete combustion of ethanol, the products are always carbon dioxide and water, and energy is released. If oxygen is limited, incomplete combustion occurs, producing carbon monoxide (CO) or soot.
| Condition | Type of Combustion | Products | Observation |
|---|---|---|---|
| Plentiful oxygen | Complete combustion | Carbon dioxide + Water | Blue flame; clean burn |
| Limited oxygen | Incomplete combustion | Carbon monoxide and/or soot + Water | Yellow, smoky flame |
Example :
Write a balanced chemical equation for the complete combustion of ethanol and state the products formed.
▶️ Answer/Explanation
Step 1: Write the formula for ethanol — \(\mathrm{C_2H_5OH}\).
Step 2: Combine with oxygen — \(\mathrm{O_2}\).
Step 3: Balance the equation: \(\mathrm{C_2H_5OH + 3O_2 → 2CO_2 + 3H_2O}\).
Step 4: Identify products — carbon dioxide and water.
Final Answer: Ethanol burns completely in oxygen to produce carbon dioxide and water with a blue flame.
Uses of Ethanol
Ethanol as a Solvent
A solvent is a substance that dissolves other substances (solutes) to form a solution. Ethanol is an excellent solvent because it can dissolve both polar and non-polar substances.
Key Uses:
- Used in perfumes and aftershaves — dissolves fragrant compounds and evaporates quickly, leaving a pleasant scent.
- Used in medicines and antiseptics — dissolves substances that are insoluble in water and also acts as a disinfectant.
- Used in inks, paints, and cosmetics as a solvent to ensure smooth mixing and application.
Explanation:
- Ethanol’s molecular structure contains both a polar –OH group and a non-polar hydrocarbon chain.
- This allows it to dissolve a wide range of organic and inorganic substances.
Ethanol as a Fuel
Ethanol is also widely used as a fuel because it burns cleanly and releases energy.
- It can be used:
- On its own as a biofuel (renewable fuel made by fermentation of sugar from plants).
- Mixed with petrol to make gasohol — reduces pollution and reliance on fossil fuels.
Chemical Equation (Complete Combustion):
\(\mathrm{C_2H_5OH + 3O_2 → 2CO_2 + 3H_2O}\)
Explanation:
- Ethanol burns with a clean blue flame producing carbon dioxide and water.
- The combustion is exothermic — it releases energy that can be used to power engines.
- As a biofuel, ethanol is considered carbon-neutral because the CO₂ released when burned is roughly balanced by the CO₂ absorbed during the growth of the plants used to produce it.
| Use | Description | Examples |
|---|---|---|
| Solvent | Dissolves both polar and non-polar substances. | Perfumes, medicines, cosmetics, inks. |
| Fuel | Burns cleanly and releases energy (exothermic reaction). | Bioethanol, gasohol, spirit burners. |
Example:
State two uses of ethanol and explain why it is suitable for each use.
▶️ Answer/Explanation
Step 1: Ethanol is used as a solvent in perfumes because it dissolves many organic compounds and evaporates quickly.
Step 2: Ethanol is used as a fuel because it burns cleanly in oxygen to produce carbon dioxide and water, releasing energy.
Final Answer: Uses — (a) as a solvent in cosmetics, (b) as a fuel in bioethanol or spirit burners.