Question

(a) How many equivalents of base would be neutralized by one mole of phthalic acid? What is the neutralization equivalent of phthalic acid? (b) What is the relation between neutralization equivalent and the number of acidic hydrogens per molecule of acid? (c) What is the neutralization equivalent of \(1,3,5\) -benzenetricarboxylic acid? Of mellitic acid, \(\mathrm{C}_{6}(\mathrm{COOH})_{6}\) ?

Short answer

(a) One mole of phthalic acid would be neutralized by two equivalents of base. The neutralization equivalent of phthalic acid is 83.07 g/mol. (b) The relation between neutralization equivalent and the number of acidic hydrogens per molecule of acid is: Neutralization equivalent = Molar mass / Number of acidic hydrogens. (c) The neutralization equivalent of 1,3,5-benzenetricarboxylic acid is 70.05 g/mol, and of mellitic acid (C6(COOH)6) is 43.03 g/mol.

Step-by-step solution

Identify the number of acidic hydrogens in phthalic acid

Phthalic acid has the molecular formula \( C_8H_6O_4 \), which can be written as \( C_6H_4(COOH)_2 \). It can be seen that phthalic acid has two acidic hydrogens (from the two carboxyl groups (COOH).

Calculate the equivalents of base required for neutralization of phthalic acid

Since there are two acidic hydrogens in phthalic acid, it will require two equivalents of base for complete neutralization.

Calculate the neutralization equivalent of phthalic acid

The neutralization equivalent is the mass of the acid that will react with one equivalent of the base. So, firstly we need to find the molar mass of phthalic acid: Molar mass of \( C_8H_6O_4 \) = (8 × 12.01) + (6 × 1.01) + (4 × 16.00) = 166.14 g/mol Since it takes two equivalents of base to neutralize one mole of phthalic acid, the neutralization equivalent is half of its molar mass: Neutralization equivalent of phthalic acid = Molar mass / Number of acidic hydrogens = 166.14 g/mol / 2 = 83.07 g/mol

Establish the relationship between neutralization equivalent and acidic hydrogens

From the above analysis, we can see that the neutralization equivalent is related to the molar mass of the acid and the number of acidic hydrogens it contains. Thus, the relationship can be given by: Neutralization equivalent = Molar mass / Number of acidic hydrogens

Calculate the neutralization equivalent of 1,3,5-benzenetricarboxylic acid

1,3,5-benzenetricarboxylic acid has the molecular formula \( C_9H_6O_6 \). It has three acidic hydrogens (from the three carboxyl groups, COOH). Molar mass of \( C_9H_6O_6 \) = (9 × 12.01) + (6 × 1.01) + (6 × 16.00) = 210.15 g/mol Using the relationship we established in Step 4: Neutralization equivalent of 1,3,5-benzenetricarboxylic acid = Molar mass / Number of acidic hydrogens = 210.15 g/mol / 3 = 70.05 g/mol

Calculate the neutralization equivalent of mellitic acid (C6(COOH)6)

Mellitic acid has the molecular formula \( C_6(COOH)_6 \). It has six acidic hydrogens (from the six carboxyl groups, COOH). Molar mass of \( C_6(COOH)_6 \) = (6 × 12.01) + (6 × 6 × 1.01) + (6 × 6 × 16.00) = 258.16 g/mol Using the relationship we established in Step 4: Neutralization equivalent of mellitic acid = Molar mass / Number of acidic hydrogens = 258.16 g/mol / 6 = 43.03 g/mol

Key concepts

Acidic Hydrogen

In acid chemistry, the term "acidic hydrogen" refers to the hydrogen atoms in a molecule that can be released as hydrogen ions (\( H^+ \)) in a solution. The presence of these hydrogen ions is what gives acids their characteristic properties.

For phthalic acid, with its formula \( C_8H_6O_4 \), each molecule contains two acidic hydrogens. It is these hydrogens that can participate in chemical reactions such as neutralization when an acid reacts with a base.

When it comes to neutralization reactions, each acidic hydrogen can react with one equivalent of a base to form water and a salt. Therefore, knowing the number of acidic hydrogens in a molecule helps determine how many moles of a base are required for neutralization.

Phthalic Acid

Phthalic acid is an aromatic dicarboxylic acid with the chemical formula \( C_8H_6O_4 \), often represented as \( C_6H_4(COOH)_2 \). It is characterized by having two carboxyl groups (\( -COOH \)) attached to a benzene ring.

These carboxyl groups are responsible for the acidic nature of phthalic acid, each contributing one hydrogen ion that can be dissociated in a chemical reaction.

In chemical synthesis, phthalic acid is known for its role in producing dyes, perfumes, and various other industrial chemicals. Because it's a diprotic acid, meaning it can donate two protons (hydrogen ions), it requires two moles of a base for full neutralization per mole of phthalic acid.

Molar Mass

The molar mass of a compound is the mass of one mole of its molecules, expressed in grams per mole (\( g/mol \)). It is determined by adding together the atomic masses of all the atoms present in the molecule.

For phthalic acid, its molecular formula \( C_8H_6O_4 \) results in a molar mass calculation of:

• 8 carbon atoms (\( C \)) at \( 12.01 \ g/mol \)= \( 96.08 \, g/mol \)
• 6 hydrogen atoms (\( H \)) at \( 1.01 \ g/mol \)= \( 6.06 \ g/mol \)
• 4 oxygen atoms (\( O \)) at \( 16.00 \ g/mol \)= \( 64.00 \ g/mol \)

Adding these values gives a total molar mass of \( 166.14 \ g/mol \). Knowing the molar mass is essential for calculating the neutralization equivalent of acidic compounds.

Carboxyl Group

The carboxyl group is a functional group present in organic acids with the formula \( -COOH \). It consists of a carbonyl group (\( C=O \)) attached to a hydroxyl group (\( OH \)).

This group is pivotal in defining the acidic characteristics of a molecule. In the presence of suitable conditions, the hydrogen atom in the hydroxyl part of the carboxyl group can be released as a hydrogen ion, resulting in an acidic reaction.

In phthalic acid, the presence of carboxyl groups is what allows the compound to release hydrogen ions during chemical reactions. This release facilitates the process of neutralization, where acids react with bases to form salts, showcasing the importance of the carboxyl group in acid-base chemistry.