Ethanol is a useful solvent because it contains both a polar and a non-polar portion within the molecule.

he polar portion consists of hydroxyl or -OH group and the non polar portion consists of the ethyl or CH₃CH₂- group.

This allows ethanol to dissolve both polar and non polar compounds. Ethanol can dissolve polar substances because of hydrogen bonds which are form with the –OH group.

Ethanol can also dissolve non-polar substances due to strong dispersion forces created between the ethyl group and the non polar substance.

Ethanol is relatively safe and is used to dissolve many organic compounds which are insoluble in water.

Ethanol –concentrated sulfuric acid→ Ethylene + Water

C₂H₅OH(l)  –concentrated H₂SO₄→ C₂H₄(g) + H₂O(l)

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

1. A solution of sugar is prepared. This could be in the form of plain sugar or fruits or grains that are mashed up.

2. The temperature is between 30-37°C. (In industry 30°C is often used as it lowers the rate of evaporation)

3. Air(oxygen) is excluded. The conditions are anaerobic.

4. A small amount of yeast nutrients such as phosphate salt is added.

5. Yeast is added. The most common yeast used is Saccharomyces cerevisiae. Once the ethanol concentration reaches 14-15% by volume, the yeast cannot survive, and the fermentation process stops.

1. Any sucrose in the mixture (plain sugar or fruits or grains) is first converted into glucose and fructose by extracellular enzymes secreted from the yeast. Sucrose + water -- enzymes from yeast→ glucose + fructose

2. Glucose and fructose (simple sugars) are then converted to ethanol by the yeast in the fermentation process.

Glucose solution --zymase from yeast→ ethanol + carbon dioxide, the chemical equations for both processes are

1. C₁₂H₂₂O₁₁ + H₂O → C₆H₁₂O₆(glucose) + C₆H₁₂O₆(fructose) and

2. C₆H₁₂O₆ –zymase→ 2C₂H₅OH + 2CO₂

1. The heat of combustion per mole increases greatly with molecular size as there is more fuel to burn.

2. The heat of combustion per gram increases slightly with molecular size. This is because the ratio of C to O atoms decreases with molecular size and there are more carbon atoms to burn.

Procedure:

1. Add a spatula of dried brewers yeast to a stoppered 250mL conical flask containing 100mL of 10% glucose solution (ie 10 g of glucose).

2. Add 1 ml of antifoaming agent to the flask and gently mix the contents.

3. Insert a fermentation lock into the stopper.

4. Incubate at 30°C.

5. Record the initial mass of the flask and then every day until there is constant mass.

6. Plot a graph of mass against time.

Note:10g of glucose solution when fermented will loose about 4 grams of carbon dioxide.

Bioethanol is produced industrially from the fermentation of sugar cane.

The sugar cane is first processed to remove the sugar by crushing, soaking and sometimes using chemical treatment.

The sugar is then fermented to ethanol using enzymes produced from yeast.

1. Sucrose -yeast enzymes→ Glucose + Fructose

2. Glucose –fermentation→ Ethanol(14%) + Carbon dioxide

3. A final step purifies the ethanol by distillation to the azeotropic form of ethanol, which is about 93% to 95% ethanol. The crushed stalk of the sugar cane, known as bagasse, contains cellulose and lignin and is often burnt as fuel in the ethanol manufacturing process.

Ethanol(14%) -distillation→ Ethanol (95%).

This is the maximum % that can be distilled.

4. Molecular sieves are used to remove the remaining water.

Ethanol(95%)  –molecular sieves → Ethanol (100%) or anhydrous alcohol

Advantages:

1. Ethanol can be added up to 10-15% in petrol fuels without harming the engine. This can help conserve fossil fuels which are non-renewable.

2. Ethanol burns cleaner than fossil fuels as each ethanol molecule contains an oxygen atom which is used in the combustion process. This reduces pollution.

C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)

3. Fossil fuels release buried carbon into the atmosphere as carbon dioxide adding to the Greenhouse effect. The burning of ethanol does not add additional carbon dioxide to the atmosphere as the biomass needed for its production would be removing carbon dioxide at the same rate. The burning of ethanol therefore does not add to Greenhouse gas emissions.

Disadvantages:

1. The disadvantages of using ethanol include need to modify fuel lines and even the engine if the ethanol is more than 10-15% when mixed with petrol.

2. Another disadvantage is the low price of still readily available petroleum. Large tracts of land would need to be allocated to growing plants to use in the production of ethanol rather than food.

3. Ethanol also can only be produced up to 14% by fermentation. The process of separating the water from ethanol requires large amounts of energy. Distillation of the aqueous ethanol to produce almost pure ethanol (96% ethanol and 4% water) can take half as much energy as that released when the ethanol is burnt.

4. Per gram, octane generates more energy than ethanol (Octane 42.0 kJ/g and ethanol only 30.6 kJ/g). This means that a much larger amount of ethanol needs to be produced and transported to achieve the same energy - and transporting 40% more fuel makes a big impact, both economically and environmentally.