Problem 38 - Chemistry and Chemical Reactivity

Question

Equal molar quantities of hydrochloric acid and sodium hypochlorite (NaCIO) are mixed. (a) Write the balanced, net ionic equation for the acid-base reaction that can, in principle, occur. (b) Does the equilibrium lie to the right or left?

Step-by-Step Solution

Answer

(a) \( H^+ + OCl^- \rightarrow HOCl \); (b) Equilibrium lies to the left.

Step 1: Identify Reactants

Hydrochloric acid (HCl) and sodium hypochlorite (NaOCl) are the reactants. In the solution, HCl exists as \( H^+ \) and \( Cl^- \), and NaOCl as \( Na^+ \) and \( OCl^- \). We can ignore \( Na^+ \) since it doesn't participate in the reaction.

Step 2: Net Ionic Equation

The net ionic equation focuses on the ions that participate. The useful reaction here is between \( H^+ \) and \( OCl^- \). The reaction forms hypochlorous acid (HOCl): \[ H^+ + OCl^- \rightarrow HOCl \] This is the balanced net ionic equation for the reaction.

Step 3: Determine Direction of Equilibrium

To determine the direction, consider the strengths of the acids and bases involved. \( HCl \) is a strong acid, dissociated fully in water, while \( HOCl \) is a weak acid. Since a strong acid reacts to form a weaker acid, the reaction equilibrium lies to the **left**.

Key Concepts

Acid-Base Reactions

Acid-base reactions are a fundamental concept in chemistry. They involve the transfer of protons between reactants, typically resulting in the formation of water and a salt. In the provided exercise, we observe an interaction between two substances: hydrochloric acid ( HCl ) and sodium hypochlorite ( NaOCl ). - Hydrochloric acid ( HCl ) dissociates completely in water to form hydrogen ions ( H^+ ) and chloride ions ( Cl^- ). - Sodium hypochlorite, on the other hand, exists as sodium ions ( Na^+ ) and hypochlorite ions ( OCl^- ). In acid-base reactions, it is the transfer of the H^+ ion that determines the outcome. Here, the H^+ reacts with the OCl^- to give hypochlorous acid ( HOCl ). Understanding this core exchange is crucial to predicting the products of such reactions.

Equilibrium Direction

The direction of equilibrium in a chemical reaction indicates where the balance of products and reactants lies when the system reaches a state of stability. For acid-base reactions, this direction is influenced by the relative strengths of the acids and bases involved. - Strong acids, like hydrochloric acid ( HCl ), dissociate completely in solution, releasing a large number of protons. - In contrast, weak acids like hypochlorous acid ( HOCl ) only partially dissociate and hence have fewer available protons. In the given reaction, a strong acid converts into a weak acid. This shift suggests a net movement back towards the reactants. Therefore, the equilibrium "lies to the left," meaning that even though the products form, the reaction will predominantly contain the strong acid and its ions.

Net Ionic Equation

Net ionic equations are invaluable tools for clearly demonstrating the species involved in a chemical reaction, by excluding the spectator ions which do not change during the reaction. This helps in honing in on the actual chemical change occurring in the solution.In the exercise, we deduce the net ionic equation by focusing on the ions that actively participate:- We start with the ions from hydrochloric acid, H^+ and OCl^- from sodium hypochlorite.- The reaction between these ions forms hypochlorous acid (HOCl):\[ H^+ + OCl^- \rightarrow HOCl \] This equation reveals that only H^+ and OCl^- contribute to the reaction, while Na^+ and Cl^- remain unchanged (as spectator ions). Recognizing these active participants simplifies understanding the main process taking place.