Question

\(p K_{a}\) of which compound is very close to \(p K_{a}\) of Butanoic acid?

Short answer

The compound with a \(p K_a\) very close to Butanoic acid is Propanoic acid, with a \(p K_a\) value of 4.87.

Step-by-step solution

Find the pKa of Butanoic acid

We need to look up the pKa value of Butanoic acid. Butanoic acid, also known as butyric acid, has a pKa of approximately 4.82.

Compare with other compounds

Let's compare the pKa value of Butanoic acid with some other common compounds: 1. Acetic acid: pKa = 4.76 2. Propanoic acid: pKa = 4.87 3. Benzoic acid: pKa = 4.20 4. Formic acid: pKa = 3.75

Determine the closest pKa value

Comparing the pKa values from step 2, we can see that Propanoic acid is the closest to Butanoic acid with a pKa value of 4.87, which is 0.05 points higher than the pKa value of Butanoic acid (4.82). Acetic acid is also close with a pKa value of 4.76, but Propanoic acid is closer. Therefore, the compound with a pKa very close to Butanoic acid is Propanoic acid.

Key concepts

Butanoic Acid

Butanoic acid, commonly known to many as butyric acid, is a carboxylic acid with the structural formula \( C_4H_8O_2 \). It's characterized by a four-carbon chain and is recognized by its unpleasant smell, often similar to rancid butter. Butanoic acid is a weaker organic acid with a \( pK_a \) value of about 4.82, which reflects its ability to donate a proton to the base in a solution.

The \( pK_a \) value is crucial as it gives us a measure of the acid strength—the lower the \( pK_a \) value, the stronger the acid. In biochemical processes, butanoic acid plays a role in various fermentation reactions and is also produced in the human gut by the bacterial fermentation of dietary fibers. Its \( pK_a \) value makes it slightly more acidic than propanoic acid but less than acetic acid.

When analyzing chemical properties or predicting the behavior of butanoic acid in various chemical reactions, understanding its acidity is fundamental. The relative acidity also implies how it may interact with other substances, its solubility in water, and its volatility.

Propanoic Acid

Propanoic acid, which has the chemical formula \( C_3H_6O_2 \), is a carboxylic acid with a three-carbon chain. Its structural simplicity makes it an excellent reference point when studying carboxylic acids in organic chemistry. With a \( pK_a \) value of 4.87, it lies very close to butanoic acid in terms of acidity.

This organic acid is found naturally in dairy products and is a byproduct of fermentation processes. It is marginally less acidic than butanoic acid, which can be attributed to the shorter carbon chain, resulting in less electron-withdrawing inductive effect and therefore a decreased ability to stabilize the negative charge formed on the carboxylate ion after deprotonation. The slight difference in \( pK_a \) values between these two acids may seem subtle, but it can have a significant impact on their behavior in chemical reactions, such as esterification or amidation.

Understanding the properties of propanoic acid not only relates to its acidity but also to its use in food preservatives due to its anti-fungal properties. Additionally, it offers insights into how structural changes, even minor ones, can affect the strength of an acid.

Acid Dissociation Constant (\( pK_a \))

The Acid Dissociation Constant, represented as \( pK_a \), is a quantitative measure of the strength of an acid in solution. It is the negative logarithm of the acid dissociation constant \( K_a \), where a lower \( pK_a \) value corresponds to a stronger acid. This concept is core to understanding the behavior of acids and bases in chemistry.

At the molecular level, \( pK_a \) is reflective of an acid's tendency to donate a proton to a base. It gives insights into chemical stability and reactivity of the acid; for example, an acid with a low \( pK_a \) readily loses a proton, making it reactive in acid-base chemical reactions.

Importance of \( pK_a \) Values

Knowing the \( pK_a \) value of a compound like butanoic or propanoic acid can help predict the degree of dissociation in a given environment, which is vital for numerous applications like drug design, food science, and chemical synthesis. A tight grasp on acidity constants also allows chemists to understand buffer systems, which are solutions that resist changes in pH upon the addition of an acid or base.

Application and Relevance

Practical applications of different \( pK_a \) values are wide-ranging, not limited to the design of pharmaceutical products where the absorption, distribution, metabolism, and excretion (ADME) characteristics of a drug can be influenced by the \( pK_a \) of its functional groups. In environmental science, \( pK_a \) helps assess the environmental fate and transport of acid-containing compounds.