Question

\(\mathrm{B}(\mathrm{OH})_{3}+\mathrm{NaOH} \leftrightarrow \mathrm{NaBO}_{2}+\mathrm{Na}\left[\mathrm{B}(\mathrm{OH})_{4}\right]+\mathrm{H}_{2} \mathrm{O}\) How can this reaction be made to proceed in forward direction? (a) Addition of cis- 1,2 -diol (b) Addition of borax (c) Addition of trans-1,2-diol (d) Addition of \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\)

Short answer

Add cis-1,2-diol to drive the reaction forward.

Step-by-step solution

Understand the Reaction

The given reaction is between boric acid (B(OH)₃) and sodium hydroxide (NaOH), resulting in the formation of sodium metaborate (NaBO₂), sodium tetrahydroxyborate (Na[B(OH)₄]), and water (H₂O). The equilibrium is dynamic, and we need to shift it to the right, meaning more products, by applying the concept of Le Chatelier's principle.

Apply Le Chatelier's Principle

According to Le Chatelier's principle, a system at equilibrium will shift to counteract any changes in concentration, pressure, or temperature. In this case, adding a reactant or removing a product can drive the reaction forward.

Analyze Effect of Each Option

(a) Addition of cis-1,2-diol: Cis-1,2-diols can form complexes with borate, which stabilizes the product side and pulls the equilibrium to the right, favoring product formation. (b) Addition of borax: Borax contains borate ions, which would increase the concentration of the borate products and potentially shift equilibrium left. (c) Addition of trans-1,2-diol: Trans-diols do not form stable complexes with borate like cis-diols do, so this option is unlikely to have the desired effect on equilibrium. (d) Addition of Na₂HPO₄: This compound does not directly interact with boric acid or its products to shift equilibrium right.

Select the Correct Option

Based on the analysis, addition of cis-1,2-diol is the most effective choice because it can form a stable complex with borate ions, thereby driving the reaction forward according to Le Chatelier's principle by removing borate ions from the solution.

Key concepts

Chemical Equilibrium

Chemical equilibrium is a state where the rate of the forward reaction equals the rate of the reverse reaction. This balance results in a stable concentration of reactants and products. Even though the reaction continues to occur in both directions, there is no net change in the amount of substances on either side. When a system reaches equilibrium, it doesn't mean that the reactants and products are in equal amounts, but rather that their proportions remain constant.
The position of equilibrium can lie toward the reactants or products, depending on factors such as concentration, temperature, and pressure. In the given boric acid and sodium hydroxide reaction, the equilibrium is dynamic, meaning it can be shifted by changing these conditions according to Le Chatelier's principle.
This principle is crucial for chemical equilibrium, as it helps predict how a change, like adding more reactants, will affect the system. It guides chemists on manipulating the conditions to favor the formation of desired products.

Boric Acid Reaction

Boric acid \(\mathrm{B}(\mathrm{OH})_3\) reacting with sodium hydroxide \(\mathrm{NaOH}\) initiates a reaction that can reach an equilibrium state. Boric acid is weak but reacts with strong bases like sodium hydroxide to form different products. The reaction produces sodium metaborate \(\mathrm{NaBO}_2\) and sodium tetrahydroxyborate \(\mathrm{Na}[\mathrm{B}(\mathrm{OH})_4]\), along with water.
This reaction's equilibrium can be shifted using various reagents, which influence the stability and concentration of products and reactants. Understanding how each reagent affects the boric acid reaction is key to predicting and controlling the chemical equilibrium.
The equilibrium at play in this reaction is sensitive, so chemists can exploit reactions like these for making substances with borate complexes, which have applications in various industrial processes.

Complex Formation

Complex formation plays a vital role in driving the boric acid and sodium hydroxide reaction forward. When additional compounds that can form complexes with borates are introduced, they stabilize the product side of the equilibrium. This stabilization lowers the product's concentration in its free form, thereby forcing the reaction to shift right to restore equilibrium.

• Complexes typically form with specific structures, and in the case of borates, certain organic compounds like cis-1,2-diols are effective in complex formation.
• When such complexes are formed, the overall concentration of borate ions in the solution effectively decreases, pulling more reaction from left to right.

Complex formation is a strategic way to control chemical equilibria, especially in reactions involving weak acids and their corresponding salts.

Sodium Hydroxide Reaction

Sodium hydroxide \(\mathrm{NaOH}\) is a strong base and reacts vigorously with acids like boric acid. This reaction causes a shift from reactants to form new products, and it is often exothermic, releasing energy.
The role of sodium hydroxide in the boric acid reaction is to donate hydroxide ions. These ions combine with boric acid to produce a series of borate products, achieving a new equilibrium.

• Using Le Chatelier’s principle, adding more sodium hydroxide will push the equilibrium towards the products due to an increase in reactant concentration.
• However, beyond a certain point, simply adding more NaOH might not significantly shift equilibrium unless there are binding agents or conditions to stabilize the product side further.

Manipulating how NaOH participates in the reaction can be crucial for practical applications, ensuring that reactions are efficiently driven toward desired outputs.