Organic Chemistry Objective Questions & Answers on “Physical Properties of Carboxylic Acids”.
1. Which of the following acids has the smallest dissociation constant?
a) CH3CHFCOOH
b) FCH2CH2COOH
c) BrCH2CH2COOH
d) CH3CHBrCOOH
Answer: c
Clarification: BrCH2CH2COOH is least acidic or has less Ka i.e., dissociation constant. It is A due to lesser -I effect of Br than F and B Br atom further away form −COOH group.
2. The vapour of a carboxylic acid HA when passed over MnO2 at 573 K yields propanone. What is the acid HA?
a) Methanoic acid
b) Ethanoic acid
c) Propanoic acid
d) Butanoic acid
Answer: b
Clarification: The vapour of ethanoic acid (HA) when passed over MnO2 at 573 K yields propanone.
3. Which acid is strongest or Which is most acidic?
a) Cl2CH.COOH
b) ClCH2COOH
c) CH3COOH
d) Cl3C.COOH
Answer: b
Clarification: Presence of -I effect chlorine atom increases the acidic nature by withdrawing electrons.
Cl3CCOOH > Cl2CHCOOH > Cl−CH2−COOH > CH3COOH
4. The acid which reduces Fehling solution is which of the following?
a) Methanoic acid
b) Ethanoic acid
c) Butanoic acid
d) Propanoic acid
Answer: a
Clarification: Methanoic acid resemble with aldehyde due to its structure. So, it reduces Fehling reagent.
5. Which class of compounds shows H-bonding even more than in alcohols?
a) Phenols
b) Carboxylic acids
c) Ethers
d) Aldehydes
Answer: b
Clarification: Forms H-bonding by means two highly electronegative atoms present in it.
6. Which of the following is the strongest acid?
a) CH3COOH
b) BrCH2COOH
c) ClCH2COOH
d) FCH2COOH
Answer: d
Clarification: Presence of -I effect fluorine atom increases the acidic nature by withdrawing electrons.
F−CH2−COOH > Cl−CH2−COOH > Br−CH2−COOH > CH3COOH.
7. The reaction of HCOOH with conc.H2SO4 gives which of the following compound?
a) CO2
b) CO
c) Oxalic acid
d) Acetic acid
Answer: b
Clarification: The reaction of HCOOH with conc.H2SO4 gives carbon monoxide and water.