Chemistry of water-ethanol mixture

Ethanol is best known as alcohol since it contains hydroxyl group (-OH) attached to alkyl carbon. Ethyl alcohol is a straight chain alcohol with molecular formula C₂H₅OH. It is mainly found in alcoholic beverages, as a pure organic solvent and as an alcohol fuel (power alcohol). Water (H₂O) and ethanol molecules mix or dissoves each other, since both the solvents are polar in nature. The Hydrogen atom of the Hydroxyl (-OH) group on ethanol and water molecules are polar. The hydrogen bond is formed between the hydrogen of -OH group of ethanol and oxygen of water molecule. Water-ethanol(EtOH) mixtures at different temperatures exhibit a wide range of dielectric constant , viscosity, density and a high degree of hydrogen bonding effects. Interaction between water and ethanol can be studied at different quantities by the measurement of conductivity over that composition range. Appropriate measurements provide useful indications of solvent-solvent interaction and solvent structure.

Mixed solvents of water-ethanol can be prepared by adding known amount of ethanol to water in volume ratio or mass ratio. Differenet percentage compositions of ethanol in water, like 10%, 20 %, 30%, 40 % etc can be prepared by mixing known volume of ethanol in water (10 % ethanol = 10 cm³ ethanol + 90 cm³ water).

Volume fractions of ethanol in water is calculated as, Volume fraction = volume of ethanol / (volume of ethanol + water)

For example 10 cm³ of ethanol is mixed with 90 cm³ of water, volume fraction of ethanol = (10 / 100) = 0.1.

The various ways in which the concentration of a mixture of ethanol and water can be specified.

Mass %

This is calculated as

Mass % = (mass ethanol x 100) / (mass ethanol + mass water)

Note that the Mass % is not dependent on the temperature at which it is measured and no temperature has to be specified when giving a strength in Mass %.

Molar %

This is calculated as

Molar % = (moles ethanol x 100) / (moles ethanol + moles water)

Note that the Molar % is not dependent on the temperature at which it is measured and no temperature has to be specified when giving a strength in Molar %.

Volume %

The Volume % is bit strange in that the Volume % of ethanol and the Volume % of water add up to more than 100. The way the Volume % of ethanol is defined is that it is the parts of ethanol to which water has been added to bring the volume to a total of 100 parts.

For example, when working at 20°C, if you took 48.00 liters of pure ethanol you would find that you would have to add 55.61 liters of water to bring the total volume to 100.00 liters. The Volume % of ethanol in this case is 48.00% and the Volume % of water is 55.61%. The total of the separate components is 103.61 liters, but has contracted to 100.00 liters.

The degree of contraction is affected by the relative quantities ot ethanol and water, and also by the temperature. For example, when working at 50°F you would find that if you again started with 48.00 liters of ethanol you would need 55.82 liters of water to bring the total to 100.00 liters. This means that when a strength is specified in Volume % the temperature has to be specified as well.

Ethanol has a significantly higher coefficient of expansion than water. This means that as the temperature varies, the volume of the ethanol portion of the mixture changes faster than that of the water portion.

Volume % , Mass % and Density of ethanol in water at 25° C

William Francis Hogg on January 06, 2020:

Excellent. Physical chemistry improves philosophy and psychology. But all three are necessary in medicine. How to integrate them is a critical question.

Glen on April 22, 2015:

I disagree with the formula 10 % ethanol = 10 cm3 ethanol + 90 cm3 water as listed on this page. When ethanol and water are mixed, there is a reduction in volume because the water molecules form close hydrogen-bonds with ethanol molecules and squeeze into spaces between ethanol molecules very closely. For this reason, in my lab the correct procedure is to make 100 mL of 10% ethanol is this:

into a volumetric flask, add 10.00 mL ethanol + water up to the 100.00 mL mark.

The “water up to the 100 mL mark” will represent slightly more than 90.00 mL of water.

In other words, if I were to add 10.00 mL ethanol + 90.00 mL water, I would get a solution that is slightly greater than 10.00% ethanol.

koustubh (author) from Mangalore, India on December 17, 2014:

Thanks

B K Karan on March 08, 2013:

Very nice article, I have got all information I wanted.

koustubh (author) from Mangalore, India on September 27, 2012:

I am explaining about water (1)

+ ethanol (2) mixture

beks13 on September 25, 2012:

so then is alcohol a mixture?

Michaela Lewis on August 20, 2012:

Im in yr 11 chemistry and we are doing this now for an assesment…this was incredibly helpful thanks a million.

sembli on July 03, 2012:

Really a good collection of ethanol water chemistry. Thanks

Juan Y Silencio on February 15, 2012:

Anyway, than5hsevthukf hk,op pek

Sumit on February 03, 2012:

Could you please cite any reference? Thanks

Raghav on June 12, 2011:

Very good article, I have got all information I wanted.

Thank you for posting such an outstanding information on ethanol-water mixtures.

Emma from Houston TX on March 04, 2011:

Ya, It is nice for physic students or bio-chemistry students

imranhaider on March 04, 2011:

explanation of water and ethanol is great information for students

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