Question

\(0.1914 \mathrm{~g}\) of an organic acid is dissolved in about \(20 \mathrm{~mL}\) of water \(25 \mathrm{~mL}\) of \(0.12 \mathrm{~N} \mathrm{NaOH}\) is required for the complete neutralization of the acid solution. The equivalent weight of the acid is: (a) \(63.8\) (b) \(64.0\) (c) \(65.8\) (d) \(66.2\)

Short answer

The equivalent weight of the acid is 63.8, option (a).

Step-by-step solution

Understand Equivalent Weight Formula

The equivalent weight of an acid is calculated by dividing the gram weight of the acid by the number of equivalents of base it reacts with. The formula is:\[\text{Equivalent Weight} = \frac{\text{Weight of acid in grams}}{\text{Number of equivalents of base}}\]

Determine the Number of Equivalents of Base

The number of equivalents of base is determined using its normality (\(N\)) and volume (\(V\) in liters):\[\text{Number of equivalents} = \text{Normality} \times \text{Volume in liters}\]Substitute the given values:\[0.12 \times \left(\frac{25}{1000}\right) = 0.003 \text{ equivalents}\]

Apply the Formula for Equivalent Weight

Insert the values into the equivalent weight formula:\[\text{Equivalent Weight} = \frac{0.1914}{0.003}\]Calculate the result:\[\text{Equivalent Weight} = 63.8\]

Determine the Closest Answer

Compare the calculated equivalent weight with the provided options. The calculated equivalent weight is 63.8, which matches option (a) 63.8.

Key concepts

Organic Chemistry

Organic chemistry studies carbon-containing compounds. It's a key field in chemistry, focusing on molecules ranging from simple methane to complex proteins. In this subject, understanding how acids and bases behave is crucial. Organic acids, in particular, are compounds with a carboxyl group \(-COOH\) that can donate a proton in a reaction. Familiarity with organic compounds' properties helps chemists design reactions and synthesize new materials. They also play a significant role in biological systems, impacting everything from cellular energy production to DNA replication.

Neutralization Reaction

A neutralization reaction is a chemical reaction between an acid and a base. The result is typically water and a salt.

In the case of our exercise, the organic acid reacts with sodium hydroxide (NaOH), a strong base. During this process:

• The acid donates protons (H\(^+\))
• The base provides hydroxide ions (OH\(^-\))
• Water (H\(_2\)O) and a salt (sodium salt of the acid) are formed

Neutralization is important in industries and laboratories to control pH levels or prepare specific compounds. Understanding this concept guides chemists in balancing reactions and predicting the outcomes of acid-base interactions.

Normality and Equivalents

Normality (N) is a concentration measure that indicates the equivalent amount of solute per liter of solution. It's essential for calculating equivalents in acid-base reactions.

Equivalent weight is calculated using normality, providing insight into a substance's reactivity. The number of equivalents is the product of normality and volume in liters.

For instance, in the exercise:

• Normality of NaOH = 0.12 N
• Volume = 25 mL (or 0.025 L)
• Equivalents = 0.12 \(\times\) 0.025 = 0.003 equivalents

Understanding these calculations is crucial for anyone working with chemical reactions, as it helps determine how much reactant is needed to fully react with another substance.

Acid-Base Reaction

Acid-base reactions are fundamental to chemistry, often involving a proton transfer. They typically result in the formation of water and salt. The strength and properties of acids and bases are central to these reactions.

Organic acids participate in such reactions readily. They tend to be weak acids, which partially dissociate in solution. Conversely, bases like NaOH are strong and fully dissociate to provide hydroxide ions.

In our exercise, the organic acid is completely neutralized by the sodium hydroxide, demonstrating a classic acid-base interaction. By examining these types of reactions, chemists can predict outcomes and design experiments that harness the interplay of acids and bases for practical applications.