Characteristics of Isopropanol Diluted With Water

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Characteristics of Isopropanol Diluted With Water
Isopropanol or rubbing alcohol mixed with water is used as a disinfectant. (chemistry image by david hughes from

Isopropanol is generally mixed with water and sold as rubbing alcohol. It is also called isopropyl alcohol and 2-propanol. The 70% isopropanol solution with 30% water is an effective disinfectant. The alcohol itself has a waterlike part to its molecular structure that allows the mixture to take up less space than the two liquids separately.

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Physical Properties of Isopropanol

Isopropanol is a clear, colourless liquid with an odour of alcohol. It has a molecular weight of 60.10 and a specific gravity of 0.877 at 20 degrees Celsius. Its vapour density is 2.1 times the density of air. It boils at 82.8 degrees Celsius and auto-ignites at 399 degrees Celsius. When frozen, it melts at minus 52.2 degrees Celsius. It is stable under normal conditions of use and is completely soluble in water.

Chemical Formula and Dilution With Water

The chemical formula for isopropanol is CH3CHOHCH3. The OH part of the molecular structure is similar to the H2O structure of water, which is of the form HOH. As a result, the OH parts of the molecules of isopropanol and water mix in a similar fashion and allow the carbon-containing parts of the isopropanol molecule to slide in between them. This means that a mixture of isopropanol and water will take up less room than the two unmixed liquids.


The low freezing point of isopropanol makes it suitable for use as a de-icing agent, in antifreeze and in ice-packs. In a 70 per cent solution with water, it is sold as rubbing alcohol and used as a disinfectant. As a solvent, it is used in many perfumed products and cosmetic preparations such as aftershave lotions, body rubs and essential oils. Because it evaporates quickly, it is used in quick-drying paints and inks and in shellac. Its solvent and rapid evaporation properties also make it useful as a window cleaner.

Toxic Effects and First Aid

Isopropanol irritates mucous membranes and eyes and causes dry skin in external applications. It is poisonous when ingested or inhaled and causes drowsiness, mental confusion, vomiting, nausea and headaches with eventual death. In the US, in 2002 for example, 8998 people were exposed to elevated levels of isopropanol, 59 of them suffered disabilities or complications and three died.

First aid for external exposure is to wash off the alcohol. For ingested alcohol, do not induce vomiting. Medical professionals should pump the stomach out and flush it with water. They may administer laxatives; kidney dialysis may be required.

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