Explain why pure dry benzoic acid does not affect a litmus paper
Litmus paper is an indicator for the presence of an acidic solution (blue litmus => red) or alkaline solution (red litmus => blue). To understand this it is important to note that for a substance to become an acid or base two conditions must apply; that is, (1) the substance of interest must have water as a solvent which (2) effects ionization of the substance to yield hydronium ions (H₃O⁺ = H⁺) for an acidic solution or hydroxide ions (OHˉ) for an alkaline solution. Since benzoic acid in solid form is not in water, it will not ionize to deliver H⁺ ions into solution and litmus will be unable to detect H⁺ ions and change color.
The H of the COOH group of C6H5COOH need H2O to dissociate.
C6H5COOH + H2O ==> C6H5COO^- + H3O^+. It's the H3O^+ that reacts with the litmus paper.
Pure dry benzoic acid does not affect a litmus paper because it is a weak acid that does not readily dissociate in water. Litmus paper is typically used to detect the presence of acidic or basic substances in a solution.
When an acidic substance is dissolved in water, it releases hydrogen ions (H+) which can react with the indicator present in the litmus paper, causing a color change. However, in the case of pure dry benzoic acid, it exists primarily in an undissociated molecular form rather than as ions when added to water.
Benzoic acid has a weak tendency to donate a hydrogen ion to the solution, resulting in a relatively low concentration of H+ ions in solution. Because of this weak acid characteristic, benzoic acid does not have a significant impact on litmus paper, as the concentration of H+ ions is not sufficient to cause a noticeable color change in the indicator on the paper.
Therefore, the lack of an effect on litmus paper by pure dry benzoic acid is due to its weak acid nature and its limited ability to release H+ ions when dissolved in water.
Pure dry benzoic acid does not affect a litmus paper because it is a weak acid and does not dissociate completely in water. In order to understand why, let's break down the process step-by-step:
1. The first thing to note is that benzoic acid, represented by the chemical formula C6H5COOH, is a weak acid. This means that it does not completely ionize or dissociate into its ionic form (H+ ions and the corresponding benzoate ions) when dissolved in water.
2. Litmus paper is an indicator that changes its color in the presence of acidic or basic solutions. It contains dyes derived from lichens, which have different molecular structures that respond to changes in pH. When the litmus paper is exposed to an acidic solution, it turns red, and when exposed to a basic solution, it turns blue.
3. The key factor in determining the effect of benzoic acid on litmus paper is its degree of ionization. Compared to strong acids like hydrochloric acid (HCl) or sulfuric acid (H2SO4), weak acids partially dissociate in water. In the case of benzoic acid, only a small fraction of the acidic molecules will release hydrogen ions (H+) into the solution.
4. Since benzoic acid does not ionize completely, it does not produce enough free hydrogen ions to significantly change the pH of the solution. As a result, the concentration of H+ ions is too low to affect the color of the litmus paper.
Therefore, when you place pure dry benzoic acid on a litmus paper, it will not cause a color change because it does not provide enough acidic properties to alter the pH of the solution and react with the litmus paper's dyes.