Reaction of Calcium Oxide with Water
Calcium oxide reacts vigorously with water to form calcium hydroxide, generating heat and producing a mildly caustic solution. When calcium oxide (CaO) contacts water (H2O), it undergoes an exothermic reaction:
CaO (s) + H2O (l) → Ca(OH)2 (aq) + heat
This results in calcium hydroxide, a strong base dissolved in water. The solution is known as lime water and has a pH typically around 12, making it capable of irritating the skin and eyes.
Properties of Calcium Hydroxide Solution
- It is mildly caustic, capable of causing redness and irritation to skin on contact.
- The solution appears clear but can form a cloudy suspension if saturated.
- Used in various applications such as water treatment, agriculture, and construction.
Safe Disposal and Neutralization
Calcium hydroxide solutions must be handled carefully during disposal to avoid environmental harm. Several methods are commonly employed:
- Neutralization with vinegar (acetic acid) converts Ca(OH)2 to calcium acetate, a less hazardous compound.
- Bubbling carbon dioxide through the solution precipitates calcium carbonate:
Ca(OH)2 + CO2 → CaCO3 (solid) + H2O
This precipitate is non-toxic and environmentally benign. It is also safe to dilute calcium hydroxide solution with plenty of water before pouring down the drain. Compared to stronger hydroxides like sodium hydroxide, it is less aggressive but still requires caution.
Production of Calcium Oxide from Calcium Carbonate
Calcium oxide is commonly manufactured by heating calcium carbonate sources such as limestone or seashells above 800 °C. This thermal decomposition is described by:
CaCO3 (s) → CaO (s) + CO2 (g)
Such high temperatures are typically achieved in industrial kilns used for cement and lime production. Home preparation is impractical due to the extreme heat needed.
Summary of Key Points
- Calcium oxide reacts exothermically with water to form calcium hydroxide, a basic and mildly caustic solution.
- Calcium hydroxide can irritate skin and should be handled with care.
- Neutralizing calcium hydroxide with vinegar or carbon dioxide forms harmless calcium carbonate for safe disposal.
- Calcium oxide is produced industrially by heating calcium carbonate above 800 °C, a process unfeasible at home.
What happens when calcium oxide reacts with water?
Calcium oxide reacts with water to form calcium hydroxide. This creates a basic solution that can irritate the skin and cause redness if contact occurs.
How can calcium hydroxide solution be safely disposed of?
You can neutralize it with vinegar or bubble carbon dioxide through it. These methods turn calcium hydroxide into calcium carbonate, a harmless substance.
Is it safe to pour calcium hydroxide solution down the drain?
Yes, if diluted with plenty of water. Calcium hydroxide is less aggressive compared to stronger hydroxides like sodium hydroxide, which are used to clean drains.
How is calcium oxide produced from calcium carbonate?
Calcium carbonate decomposes to calcium oxide when heated above 800°C. This high temperature is typically reached in industrial concrete kilns.
Can calcium oxide be made at home by heating shells?
No. The temperature needed to convert shells (calcium carbonate) to calcium oxide is too high for typical home equipment. This process is usually done industrially.
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