Question

Write the approximate net reaction between carbonate ion and water in a system that is not also exposed to atmospheric carbon dioxide. Is the resulting water acidic, alkaline, or neutral?

Short answer

The net reaction between carbonate ion and water results in an alkaline solution.

Step-by-step solution

Identify the species involved

In the system described, we are primarily concerned with the carbonate ion (\(\text{CO}_3^{2-}\)) and water (\(\text{H}_2\text{O}\)). Our goal is to understand their interaction.

Write the chemical equations

The carbonate ion can react with water in two possible ways - either gaining a proton to form bicarbonate (\(\text{HCO}_3^-\)) or hydroxide ion (\(\text{OH}^-\)). The possible equilibrium reactions are: 1. \(\text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^- + \text{OH}^-\)2. This reaction shows the base nature as it involves the formation of \(\text{OH}^-\).

Assess the resulting pH

The production of \(\text{OH}^-\) ions in the solution suggests that the solution will have more hydroxide ions than hydrogen ions, making it alkaline.

Key concepts

Acid-Base Reactions

Acid-base reactions are chemical reactions that involve the transfer of protons from one substance to another. In these reactions, an acid donates a proton (\( H^+ \)) to a base, which accepts it. In the context of carbonate ion reactions with water, the carbonate ion (\( \text{CO}_3^{2-} \)) acts as a base.When carbonate ions interact with water, they can accept a proton from water, which is acting like an acid in this scenario. The chemical equation for this reaction can be written as:\[\text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^- + \text{OH}^-\]In this equilibrium reaction, the carbonate ion gains a proton to form bicarbonate (\( \text{HCO}_3^- \)) and produces hydroxide ions (\( \text{OH}^- \)). This shows that carbonate ions act as a base in water, which leads to the production of hydroxide ions, making the solution more alkaline.Understanding this kind of reaction is important in many fields, such as environmental science and geology, where carbonate compounds interact with natural water systems.

Chemical Equilibrium

Chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction, leading to constant concentrations of reactants and products. In the case of carbonate ions reacting with water, equilibrium is reached when:\[\text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^- + \text{OH}^-\]At equilibrium, there are stable concentrations of carbonate ions, bicarbonate ions, and hydroxide ions. This balance doesn't mean the reactions have stopped; rather, they occur at equal rates in both directions, so there's no net change.Let's summarize the characteristics of chemical equilibrium:- Concentrations of substances remain constant over time.- The system is balanced, with no preferential direction of reaction.- Equilibrium can be shifted by changes, such as addition of reactants or products.Studying equilibrium helps us understand how reactions can be influenced by different conditions. This is crucial in predicting the effects of environmental and chemical changes in systems containing carbonate ions.

pH Levels

The pH scale measures the acidity or alkalinity of a solution. It's a log scale based on the concentration of hydrogen ions (\( H^+ \)) in a solution. Neutral solutions have a pH of 7, acidic solutions have pH values less than 7, and alkaline solutions have pH values greater than 7.In the reaction involving carbonate ions (\( \text{CO}_3^{2-} \)) and water, the formation of hydroxide ions (\( \text{OH}^- \)) makes the solution alkaline. This means the pH is greater than 7.As hydroxide ions increase in concentration, they decrease the concentration of hydrogen ions, which results in an alkaline pH. Here's a quick overview of how pH is affected in this context:- High hydroxide ion concentration results in high pH (alkaline).- The relationship between \( [H^+] \) and \( [OH^-] \) is inversely proportional.Understanding pH is crucial for various applications, from environmental monitoring to understanding biological systems. In the case of carbonate and water, the increase in \( \text{OH}^- \) shifts the pH towards being more alkaline.