Local Preparation of Alcohols

In Tanzania and many African countries, alcohols are prepared locally through fermentation. This method has been used for centuries.

Raw materials used in Tanzania:

• Cassava
• Millet
• Maize
• Sugar beet
• Fruits (like bananas)

The Fermentation Process:

1. Starch from the raw material is converted into sugars (mainly maltose and glucose)
2. Yeast cells are added to the sugary solution
3. Yeast enzymes catalyze the breakdown of sugars into ethanol and carbon dioxide

Word equation: $葡萄糖 + 酵母 \rightarrow 乙醇 + 二氧化碳$

Chemical equation: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$

Procedure for local alcohol preparation:

1. Crush the starchy material (cassava or millet) and soak in water
2. Allow natural fermentation to occur using wild yeast from the environment
3. The mixture is left for several days at room temperature (25-30°C)
4. The liquid portion containing alcohol is separated

This produces a weak alcoholic drink (traditionally called chang'aa or similar local brews).

Industrial Preparation of Alcohols

Industrial alcohol production follows the same fermentation principle but uses controlled conditions and better equipment.

Industrial raw materials:

• Molasses (from sugar cane)
• Corn starch
• Maltose sugar ($C_{12}H_{22}O_{11}$)

Industrial process steps:

1. Starch conversion: Starch is treated with enzymes (diastase) to convert it into maltose sugar $淀粉 + 水 \xrightarrow{ diastase } 麦芽糖$

2. Fermentation: Yeast is added to ferment maltose into ethanol $麦芽糖 + 酵母 \rightarrow 乙醇 + 二氧化碳$

3. Distillation: The fermented mixture is heated in a distiller. Ethanol boils at 78°C while water boils at 100°C, so ethanol evaporates first and is collected.

Types of industrial alcohol products:

• Beer: 2-6% ethanol (from barley fermentation)
• Wine: About 10% ethanol (from grape fermentation)
• Spirits: 40-50% ethanol (after distillation)

Local Preparation of Hydrocarbons

In Tanzania, simple hydrocarbon preparations are demonstrated in the laboratory rather than produced locally for consumption.

Laboratory preparation of alkanes:

Alkanes can be prepared by the decarboxylation of sodium salts of carboxylic acids (sodium acetate + sodium hydroxide).

Reaction: $CH_3COONa + NaOH \rightarrow CH_4 + Na_2CO_3$

This reaction requires heating calcium oxide with sodium acetate.

Industrial Preparation of Hydrocarbons

1. Alkanes from Crude Oil (Fractional Distillation)

Crude oil is the main source of alkanes industrially. The process is called fractional distillation.

Procedure:

1. Crude oil is heated to about 400°C in a furnace
2. The vaporized oil enters a fractionating column
3. Different fractions condense at different heights based on boiling points
4. Lighter fractions (gases) rise to the top
5. Heavier fractions (tar) remain at the bottom

Main fractions obtained:

2. Alkenes from Cracking

Cracking is the process of breaking larger alkanes into smaller, more useful alkenes and alkanes. This is done industrially by heating alkanes with a catalyst (silicon dioxide or aluminum oxide) at high temperature.

Example - Cracking of decane: $C_{10}H_{22} \xrightarrow{高温/催化剂} C_5H_{12} + C_5H_{10}$

The pentene (C_5H_{10) produced is an alkene used to make plastics.

3. Alkenes from Dehydration of Alcohols

Alcohols can be dehydrated (water removed) to form alkenes in the laboratory and industry.

Reaction: $C_2H_5OH \xrightarrow{浓硫酸/170°C} CH_2=CH_2 + H_2O$

Concentrated sulfuric acid acts as a dehydrating agent at 170°C.

Objective

To demonstrate the local preparation of ethanol through fermentation.

Materials Required

• Sugar solution (or crushed ripe bananas)
• Yeast powder
• Warm water (35-40°C)
• conical flask
• Delivery tube
• Lime water
• Distillation apparatus (for later)

Procedure

1. Prepare 100 mL of sugar solution in a conical flask
2. Add a teaspoon of yeast to the solution
3. Fit a delivery tube into the flask and place the other end in lime water
4. Keep the mixture warm (not hot) for 2-3 days
5. Observe bubbles in the lime water (confirms $CO_2$ production)
6. After fermentation, distill the liquid to obtain ethanol

Observations

• Bubbles form in the lime water (turns milky due to $CO_2$)
• The smell of alcohol becomes noticeable after distillation

Writing the Laboratory Report

A good report should include:

1. Aim: What you wanted to achieve
2. Materials: List all chemicals and apparatus
3. Procedure: Step-by-step what you did
4. Observations: What you saw happening
5. Discussion: Explain the results using equations
6. Conclusion: What the experiment showed

In Tanzania, fractional distillation of crude oil at the Jongo Oil Refinery in Mtwara produces various fuels including petrol and kerosene that power vehicles and generators across the country. Locally, the fermentation of cassava or millet to produce traditional alcoholic beverages is a common practice in many villages, demonstrating how chemistry is applied in everyday life for both economic and cultural purposes. Understanding these preparation methods helps students appreciate the science behind the fuels they use and the drinks their communities produce.