Shortcut Methods and Tricks to Solve Alcohol Numericals

Alcohols

JEE Numerical’s

• Calculating the molecular weight of an alcohol: Use the atomic masses of carbon (12.01 g/mol), hydrogen (1.008 g/mol), and oxygen (16.00 g/mol) to find the total atomic mass of the alcohol. For example, the molecular weight of ethanol (CH3CH2OH) is:

$$(3\times 12.01\text{ g/mol})+(7\times 1.008\text{ g/mol})+(1\times 16.00\text{ g/mol})=46.07\text{ g/mol}$$

• Calculating the boiling point of an alcohol: Use the formula:

$$BoilingPoint=78.5+1.9(numberofcarbonatoms)$$

For example, the boiling point of ethanol is:

$$78.5+1.9(2)=83.3°\text{C}$$

• Calculating the solubility of an alcohol: Use the formula:

$$Solubility=\frac{100}{1+0.04(numberofcarbonatoms)}$$

For example, the solubility of ethanol in water is:

$$\frac{100}{1+0.04(2)}=\frac{100}{1.08}=92.6\text{\%}$$

• Calculating the acidity of an alcohol: Use the formula:

$$pKa=15.5-\log (K_a)$$

where (K_a) is the acid dissociation constant of the alcohol. For example, the (pK_a) of ethanol is:

$$pKa=15.5-\log (1.3\times {10}^{-16})=15.5+15.89=31.39$$

CBSE Board Exam Numericals

• Identifying the functional group of an alcohol: Look for the -OH group in the structural formula. If the molecule has a -OH group, it is an alcohol.

• Writing the chemical formula of an alcohol: Determine the number of carbon, hydrogen, and oxygen atoms in the alcohol molecule and write the chemical formula accordingly. For example, ethanol has 2 carbon atoms, 6 hydrogen atoms, and 1 oxygen atom, so its chemical formula is (C_2H_6O).

• Drawing the structural formula of an alcohol: Draw a chain of carbon atoms and attach hydrogen atoms to each carbon atom. Then, attach the -OH group to one of the carbon atoms. For example, the structural formula of ethanol is:

CH3-CH2-OH

• Naming an alcohol: Use the IUPAC nomenclature rules to name the alcohol. The root name of the alcohol is based on the number of carbon atoms in the longest carbon chain. The suffix “-ol” is added to the root name to indicate that the molecule is an alcohol. For example, the IUPAC name of ethanol is “ethanol”.