Sample Questions on Functional Groups

Question 1: Write the molecular formula for the alcohol group with 4 carbon atoms.

Answer:

The molecular formula for the alcohol group is C_nH_2n+1OH. If there are 4 carbon atoms then n=4, this means C₄H₂₍₄₎₊₁OH or C₄H₉OH. So the required molecular formula is C₄H₉OH

Question 2: Can the compound C₂H₄O be a ketone group?

Answer:

A ketone must have at least three carbon atoms in its molecules, one ketone group carbon atom, and two carbon atoms on both sides. Ketones with less than three carbon atoms are not really possible. In the given compound, we have 2 carbon atoms, so it is not a ketone group.

Question 3: What is the molecular formula of aldehyde which is derived from butane?

Answer:

Aldehydes have the general molecular formula C_nH_2nO, where n is the number of carbon atoms in one molecule. Since butane C₄H₁₀ has 4 carbon atoms, so n=4, this means C₄H₂₍₄₎O or C₄H₈O. Hence the molecular formula of aldehyde which is derived from butane is C₄H₈O.

Question 4: Identify the functional group present in the compound C₃H₈O.

Answer:

In the given compound C₃H₈O, the number of carbon atoms is 3, so n=3. First check if it satisfies the molecular formula of alcohol, aldehyde, ketone, or carboxylic acids. Since it has only one oxygen atom, so it cannot be a carboxylic group. Alcohol has the general molecular formula C_nH_2n+1OH, where n is the number of carbon atoms in one molecule. Put n=3 in this formula, we get C₃H₂₍₃₎₊₁OH or C₃H₇OH or C₃H₈O which matches the given compound. So the given compound have alcohol as its functional group.

Question 5: Write the molecular formula for the alkene group and alkyne groups containing 5 carbon atoms.

Answer:

Given that there are 5 carbon atoms, so n=5. Alkenes have the general formula C_nH_2n, where n is the number of carbon atoms in one molecule. Put n=5 in this formula, C₅H₂₍₅₎ or C₅H₁₀.

Alkynes have the general formula C_nH_2n-2, where n is the number of carbon atoms in one molecule. Put n=5 in this formula, so C₅H₈ or C₅H₈.

Hence the molecular formula for the alkene group is C₅H₁₀ and the alkyne group is C₅H₈.

Read More,

• Classification of Organic Compounds
• Haloalkanes and Haloarenes

Functional Groups if added to hydrocarbons change their functionality and properties. A hydrocarbon is a compound made up of hydrogen and carbon, which can be either saturated or unsaturated. A saturated hydrocarbon is one in which the carbon atoms are joined by only a single bond and an unsaturated hydrocarbon is one in which a double or triple bond between carbon atoms is present. Generally, a saturated hydrocarbon is very less reactive, but when another ‘atom’ or ‘group of atoms’ is attached to it, the resulting molecule becomes highly reactive depending on the attached group. The other ‘atom’ or ‘group of atoms in a carbon compound is called a functional group.