Physical properties of carboxylic acid

Physical properties of carboxylic acid p174-176

By ALICE Moe

Multiple Choice

Which of the properties of carboxylic acid increase when going down the homologous series?

• Boiling point

• Solubility

Multiple Choice

Which of the following compounds has the highest boiling point?

• Propanol

• Ethanoic acid

• Butane

• Propanal

​Boiling points of different functional groups

​Propanol (M_r 60): polar, form one hydrogen bond between molecules

Ethanoic acid (M_r 60): polar, form two hydrogen bonds between molecules

Butane (M_r 58): non-polar, form induced dipole between molecules

Propanal (M_r 58)​: polar, form permanent dipole between molecules

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Strength: induced dipole<permanent dipole<hydrogen bond​

Sem 3 Chemistry​

Chapter 7​

Multiple Choice

Why benzoic acid is a white precipitate in water?

• Its insoluble in water due to the K_a value is low

• It is insoluble in water due to the benzene ring is hydrophobic

• It is insoluble in water due to high melting point

• It is insoluble in water due to the K_sp value is low

Multiple Choice

Which of the following carboxylic acid is the strongest acid?

• Methanoic acid

• Ethanoic acid

• Benzoic acid

• Propanoic acid

​Acidity of carboxylic acid

Methanoic acid: 3.75

Ethanoic acid: 4.74

Propanoic acid: 4.81

Benzoic acid: 4.19​

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Sem 3 Chemistry

Chapter 7​

• Alkyl group is electron donating group/+ve inductive effect

• longer alkyl chain, stronger electron donating effect​

• Benzene ring is electron withdrawing group/-ve inductive effect​

Multiple Choice

Which of the following benzoic acid is the weakest acid?

• Benzoic acid

• p-methylbenzoic acid

• p-chlorobenzoic acid

• p-nitrobenzoic acid

​Acidity of benzoic acid

• the presence of electron donating group such as -CH₃ in benzene ring will decrease the acidity of benzoic acid

• -CH₃ increase electron density in benzene ring and increase polarity of O-H bond/strengthen the O-H bond

• the presence of electron withdrawing group such as -Cl, -NO₂ in benzene ring will increase the acidity of benzoic acid

• -Cl and -NO₂ decrease electron density in benzene ring and decrease polarity of O-H bond/weaken the O-H bond

Sem 3 Chemistry​

Chapter 7​

Multiple Choice

Which of the following carboxylic acid is the strongest acid?

• ethanoic acid

• chloroethanoic acid

• 4-chlorobutanoic acid

Effect of distance of substituent toward acidity of carboxylic acid​

the further the halogen from the carboxyl, the weaker the carboxylic acid​

Sem 3 Chemistry​

Chapter 7​

Multiple Choice

Which of the following carboxylic acid is the strongest acid?

• Ethanoic acid

• Chloroethanoic acid

• Dichloroethanoic acid

• Trichloroethanoic acid

​Effect of number of substituent towards acidity of carboxylic acid

The higher the number of halogen, the higher the acidity

Sem 3 Chemistry​

Chapter 7​