Properties of Ethanol

Physical Properties of Ethanol

Ethanol is a colourless liquid commonly found in alcoholic drinks and used in industry. It has a boiling point of about 786C, which is lower than water6s boiling point (1006C). This means ethanol evaporates more easily and is volatile.

Ethanol is miscible with water, meaning it can mix with water in any proportion without separating. This is because ethanol molecules can form hydrogen bonds with water molecules.

It is also flammable, so it burns easily in air, producing a clean blue flame. This makes it useful as a fuel.

Chemical Properties of Ethanol

Ethanol undergoes several important chemical reactions:

Combustion

When ethanol burns in oxygen, it reacts completely to form carbon dioxide and water:

$\mathrm{C_2H_5OH} + 3\mathrm{O_2} \rightarrow 2\mathrm{CO_2} + 3\mathrm{H_2O}$

This reaction releases energy, which is why ethanol can be used as a fuel.

For instance, if ethanol is burned in a spirit burner, the heat released can be used to heat water.

Reaction with Sodium

Ethanol reacts with sodium metal to produce hydrogen gas and sodium ethoxide:

$\mathrm{2C_2H_5OH} + 2\mathrm{Na} \rightarrow 2\mathrm{C_2H_5ONa} + \mathrm{H_2}$

This reaction is similar to sodium6s reaction with water but slower. The hydrogen gas produced can be tested by a squeaky pop test.

Oxidation to Ethanoic Acid

Ethanol can be oxidised (usually using an acidified potassium dichromate solution) to form ethanoic acid (vinegar):

$\mathrm{C_2H_5OH} + [O] \rightarrow \mathrm{CH_3COOH} + \mathrm{H_2O}$

Note: [O] represents the oxidising agent, typically acidified potassium dichromate.

The orange dichromate ions ($\mathrm{Cr_2O_7^{2-}}$) turn green as they are reduced during this process.

This reaction is important in the production of vinegar from ethanol by fermentation.

Dehydration to Form Ethene

Ethanol can lose water (dehydrate) when heated with an acid catalyst like concentrated sulfuric acid to form ethene, an alkene:

$\mathrm{C_2H_5OH} \xrightarrow[\text{heat}]{\mathrm{H_2SO_4}} \mathrm{C_2H_4} + \mathrm{H_2O}$

This reaction is reversible and is used in industry to produce ethene from ethanol.

For example, when ethanol is heated with concentrated sulfuric acid, ethene gas is produced, which can be tested by its ability to turn bromine water from orange to colourless.

Uses of Ethanol

Ethanol has many practical uses:

• Solvent: Ethanol dissolves many substances and is used in industry and laboratories to dissolve chemicals and in cleaning products.
• Alcoholic drinks: It is the active ingredient in beer, wine, and spirits.
• Fuel and biofuel: Ethanol burns cleanly and is used as a renewable fuel, often blended with petrol in cars (e.g., E10 fuel).
• Antiseptic and disinfectant: Ethanol kills bacteria and viruses, so it is used in hand sanitizers and medical wipes.

Learning Example: Calculating the Volume of Carbon Dioxide Produced by Combustion of Ethanol

If 46 g of ethanol ($\mathrm{C_2H_5OH}$) is completely burned, how many grams of carbon dioxide are produced?

Step 1: Calculate moles of ethanol. Molar mass of ethanol = $2 \times 12 + 6 \times 1 + 1 \times 16 = 46 \text{ g/mol}$.

$\text{Moles of ethanol} = \frac{46}{46} = 1 \text{ mole}$

Step 2: From the balanced equation, 1 mole of ethanol produces 2 moles of $\mathrm{CO_2}$.

Step 3: Calculate mass of $\mathrm{CO_2}$. Molar mass of $\mathrm{CO_2} = 12 + 2 \times 16 = 44 \text{ g/mol}$.

Mass of $\mathrm{CO_2} = 2 \times 44 = 88 \text{ g}$.

So, burning 46 g of ethanol produces 88 g of carbon dioxide.