Problem 51 - Chemistry The Central Science

Question

Write a balanced chemical equation using condensed structural formulas for the saponification (base hydrolysis) of (a) methyl propionate, (b) phenyl acetate.

Step-by-Step Solution

Answer

(a) Methyl propionate saponification: \(CH3CH2COOCH3 + OH^- \rightarrow CH3OH + CH3CH2COO^-\) (b) Phenyl acetate saponification: \(C6H5COOCH3 + OH^- \rightarrow CH3OH + C6H5COO^-\)

Step 1: Write the condensed structural formula of the ester (methyl propionate)

The condensed structural formula of methyl propionate is CH3CH2COOCH3.

Step 2: Write the balanced chemical equation for the saponification of methyl propionate

The saponification reaction generally involves the reaction of an ester with a base (usually a hydroxide ion, OH-) to produce an alcohol and a carboxylate ion. The balanced chemical equation for the saponification of methyl propionate is: CH3CH2COOCH3 + OH- → CH3OH + CH3CH2COO- In this case, methyl propionate reacts with hydroxide ions to produce methanol and propionate ions. (b) Saponification of Phenyl Acetate

Step 1: Write the condensed structural formula of the ester (phenyl acetate)

The condensed structural formula of phenyl acetate is C6H5COOCH3.

Step 2: Write the balanced chemical equation for the saponification of phenyl acetate

The saponification reaction again involves the reaction of an ester (phenyl acetate) with a base (a hydroxide ion, OH-) to produce an alcohol and a carboxylate ion. The balanced chemical equation for the saponification of phenyl acetate is: C6H5COOCH3 + OH- → CH3OH + C6H5COO- In this case, phenyl acetate reacts with hydroxide ions to produce methanol and phenylacetic acid ions.

Key Concepts

Balanced Chemical Equation

A balanced chemical equation is vital in the study of chemistry as it represents the law of conservation of mass, ensuring that the number of atoms for each element is equal on both the reactant and product sides of the equation. In the context of saponification, a type of ester hydrolysis, the balanced equation illustrates the transformation of an ester into an alcohol and a carboxylate ion when reacting with a base, typically a hydroxide ion (OH-).

For example, in the saponification of methyl propionate, the balanced chemical equation is: \[ CH_3CH_2COOCH_3 + OH^- \rightarrow CH_3OH + CH_3CH_2COO^- \]

Ensuring the equation is balanced requires equal numbers of carbon, hydrogen, and oxygen atoms on both sides. This accurate representation of the reaction is crucial for students to understand the stoichiometry, which is the quantitative relationship between reactants and products in a chemical reaction.

Ester Hydrolysis

Ester hydrolysis is a chemical reaction where an ester bond is broken down by water, a process that can be accelerated by adding an acid or a base. In the context of our discussion, we focus on base-catalyzed ester hydrolysis, commonly known as saponification. This particular reaction is important in creating soaps from fats and oils, which are esters of fatty acids.

During saponification, the ester reacts with a hydroxide ion, resulting in the formation of an alcohol and a carboxylate ion. For instance, in the hydrolysis of phenyl acetate:\[ C_6H_5COOCH_3 + OH^- \rightarrow CH_3OH + C_6H_5COO^- \.\]

Understanding the concept of hydrolysis in chemistry is essential as it governs many biological processes as well as industrial applications, such as the production of soaps and the breakdown of biopolymers.

Condensed Structural Formulas

Condensed structural formulas are a type of chemical shorthand to convey the arrangement of atoms within a molecule without drawing full structural diagrams. These formulas are especially useful in organic chemistry, where carbon compounds often have complex structures.

When writing condensed structural formulas, groups of atoms bonded together may be clustered as a single unit. For example, the ester methyl propionate has the condensed structural formula \( CH_3CH_2COOCH_3 \), where \( CH_3CH_2 \) represents a propyl group and \( COOCH_3 \) represents the ester functional group bonded to the methyl group. Similarly, phenyl acetate's condensed formula is \( C_6H_5COOCH_3 \), linking the phenyl group (\( C_6H_5 \)) with the ester linkage to a methyl group (\( COOCH_3 \)).

Grasping these formulas allows students to more easily visualize and understand chemical reactions without the complexities of drawing detailed structures for each compound involved in the reaction.