When sulfuric acid reacts with potassium chloride, hydrochloric acid (HCl) and potassium bisulfate (KHSO4) are produced. This reaction is a classic example of an acid-salt displacement, where a stronger, less volatile acid (sulfuric acid) displaces a weaker, more volatile acid (hydrochloric acid) from its salt.
The Chemical Reaction Explained
The interaction between sulfuric acid ($\text{H}_2\text{SO}_4$) and potassium chloride ($\text{KCl}$) results in a double displacement reaction. In this process, the hydrogen from sulfuric acid combines with the chloride from potassium chloride to form hydrochloric acid, while the potassium from potassium chloride combines with the bisulfate ion from sulfuric acid to form potassium bisulfate.
The chemical equation for this reaction is:
$\text{KCl (s/aq)} + \text{H}_2\text{SO}_4 \text{ (aq)} \rightarrow \text{HCl (g)} + \text{KHSO}_4 \text{ (aq)}$
- Reactants:
- Potassium Chloride ($\text{KCl}$): A common ionic salt, typically found as a white crystalline solid.
- Sulfuric Acid ($\text{H}_2\text{SO}_4$): A strong mineral acid, often used in concentrated form for this reaction.
- Products:
- Hydrochloric Acid ($\text{HCl}$): A strong, corrosive acid. In this reaction, especially when concentrated sulfuric acid is used and heated, it often evolves as a pungent gas.
- Potassium Bisulfate ($\text{KHSO}_4$): Also known as potassium hydrogen sulfate, it is an acidic salt that typically remains in the solution.
Balancing the Equation
As highlighted in a YouTube video explaining this specific reaction, the reaction between $\text{KCl}$ and $\text{H}_2\text{SO}_4$ to form $\text{HCl}$ and $\text{KHSO}_4$ is often considered already balanced in its simplest form, with a 1:1:1:1 stoichiometric ratio for each reactant and product. The video notes that where people commonly encounter problems during balancing is when they might miscount hydrogens or other elements, but for this specific equation, it is straightforward.
Key Aspects and Applications
- Preparation of Hydrogen Chloride Gas: This reaction is a common laboratory method for generating hydrogen chloride gas. By using concentrated sulfuric acid, which is non-volatile, the more volatile $\text{HCl}$ gas can be easily driven off and collected, particularly when the reaction mixture is gently heated.
- Acid Displacement: This is a classic example of an acid displacement reaction. Sulfuric acid is stronger and less volatile than hydrochloric acid, allowing it to "push out" the $\text{HCl}$ from its salt.
- Conditions: The reaction can occur at room temperature, but heating often facilitates the complete evolution of $\text{HCl}$ gas. The use of concentrated sulfuric acid is crucial for efficient $\text{HCl}$ production.
Summary of the Reaction
| Aspect | Description |
|---|---|
| Reaction Type | Double Displacement, Acid-Salt Reaction |
| Reactants | Potassium Chloride ($\text{KCl}$), Sulfuric Acid ($\text{H}_2\text{SO}_4$) |
| Products | Hydrochloric Acid ($\text{HCl}$), Potassium Bisulfate ($\text{KHSO}_4$) |
| Equation | $\text{KCl (s/aq)} + \text{H}_2\text{SO}_4 \text{ (aq)} \rightarrow \text{HCl (g)} + \text{KHSO}_4 \text{ (aq)}$ |
| Observations | Evolution of a pungent gas ($\text{HCl}$), formation of a soluble salt (Potassium Bisulfate) |
| Common Use | Laboratory preparation of hydrogen chloride gas |
This reaction demonstrates fundamental principles of chemical reactivity and is an important method for producing hydrogen chloride.
