Write an equation for the acid-base reaction between 2,4-pentanedione and sodium ethoxide, and calculate its equilibrium constant, \(K_{\text {eq. }}\). The \(\mathrm{p} K_{\mathrm{a}}\) of 2,4 -pentanedione is 9 ; that of ethanol is \(15.9\). 2,4-Pentanedione Sodium ethoxide

Understanding acid-base reactions is essential as they are ubiquitous in chemistry, including organic reactions and biological processes. At the heart of an acid-base reaction is the transfer of a proton (a hydrogen atom that has lost its electron) from the acid to the base. Acids can donate protons because they have a proton available to release, while bases are proton acceptors.

In the case of the reaction between 2,4-pentanedione, a weak acid, and sodium ethoxide, a strong base, the 2,4-pentanedione donates a proton to the sodium ethoxide. It's important to visualize this process: the acid ends up deprotonated, resulting in a carbanion, and the base becomes protonated, yielding the conjugate acid, in this case, sodium ethanol. Once recognized, this pattern paves the way to predict the products of similar acid-base reactions.

Grasping the relationship between Ka and pKa is critical for analyzing acidity and the strength of an acid. The acid dissociation constant, Ka, quantifies the strength of an acid in solution, representing the ratio of the concentration of the products to the reactants for a given acid-base reaction at equilibrium. However, since Ka values can span many orders of magnitude, pKa values are used for convenience, where pKa = -log10(Ka).

Accordingly, a lower pKa indicates a stronger acid, since it implies a larger Ka value. In calculations, you frequently need to revert pKa to Ka to use in various formulae. The inverse operation, Ka = 10^-pKa, allows you to switch from the logarithmic scale back to the straightforward dissociation constant necessary for equilibrium calculations.

The equilibrium constant (Keq) is the quantifier of the position of equilibrium in a chemical reaction, in particular for reversible reactions. It is a ratio of the concentration of the products over the concentration of the reactants at equilibrium, each raised to the power of their respective coefficients in the balanced chemical equation.

Consider the given exercise: calculating Keq involves leveraging both the strength of the acid and the base through their respective Ka values. By dividing the Ka of the acid by the Ka of the base, you get the equilibrium constant for the overall reaction. This ratio tells us the extent to which the reaction favors products over reactants. Here, we see a Keq significantly greater than 1, signifying the reaction greatly favors the formation of products — in this case, the ethoxide ion of 2,4-pentanedione and sodium ethanol.