What happens when: (2) Calcium hydroxide Ca(OH)2 dissolves in water؟
إجابة الطالب المختصرة من خلال موقع بوابة الإجابات هي
Limited Solubility: Calcium hydroxide is sparingly soluble in water, forming a weakly alkaline solution known as lime water. Alkaline Nature: The solution contains hydroxide ions (OH⁻), making it basic, which can turn red litmus paper blue. Cloudy Precipitate with CO₂: If carbon dioxide (CO₂) is bubbled through lime water, it reacts to form calcium carbonate (CaCO₃), which appears as a milky white precipitate
When calcium hydroxide, Ca(OH)₂, dissolves in water, it undergoes a process called **dissociation**. Here's a breakdown of what happens:
1. **Dissolution:** Solid calcium hydroxide, a white powder, starts to disperse within the water. The water molecules begin to interact with the ions that make up the solid Ca(OH)₂.
2. **Dissociation (Ionization):** Ca(OH)₂ is an ionic compound, meaning it's held together by ionic bonds between calcium ions (Ca²⁺) and hydroxide ions (OH⁻). When it dissolves, these ionic bonds break, and the Ca²⁺ and OH⁻ ions separate and become surrounded by water molecules. This process is represented by the following equilibrium reaction:
```
Ca(OH)₂(s) ⇌ Ca²⁺(aq) + 2OH⁻(aq)
```
* `Ca(OH)₂(s)` represents solid calcium hydroxide.
* `Ca²⁺(aq)` represents calcium ions dissolved in water (aqueous).
* `OH⁻(aq)` represents hydroxide ions dissolved in water (aqueous).
* The double arrow (⇌) indicates that the dissolution is an equilibrium process. This means that solid Ca(OH)₂ is dissolving and ions are precipitating back into solid at the same time. Eventually, a point is reached where the rates of dissolution and precipitation are equal, and the solution is saturated.
3. **Hydration (Solvation):** The water molecules surround the individual Ca²⁺ and OH⁻ ions. The slightly negative oxygen atoms in water are attracted to the positive calcium ions (Ca²⁺), and the slightly positive hydrogen atoms in water are attracted to the negative hydroxide ions (OH⁻). This process is called hydration (or solvation, more generally) and helps to stabilize the ions in solution, preventing them from re-associating.
4. **Formation of a Basic Solution:** The release of hydroxide ions (OH⁻) into the water increases the concentration of OH⁻ ions in the solution. An increase in hydroxide ion concentration makes the solution basic (alkaline). The pH of the solution will be greater than 7.
5. **Limited Solubility:** Calcium hydroxide is only sparingly soluble in water. This means that only a small amount of it will dissolve before the solution becomes saturated. The solubility of Ca(OH)₂ decreases as the temperature increases.
**In Summary:**
When calcium hydroxide dissolves in water, it dissociates into calcium ions (Ca²⁺) and hydroxide ions (OH⁻), which are then surrounded and stabilized by water molecules. The increased concentration of hydroxide ions makes the solution basic. The solubility of calcium hydroxide is limited and decreases with increasing temperature. The solution formed is often called "limewater."
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