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Before understanding CaO as an alkali or a base. Let’s understand what bases and alkali are.
What is a Base?
In simple terms, a base is a substance that can accept a proton or donate an electron pair. When dissolved in water, bases typically produce hydroxide ions. Bases have a pH greater than 7, feel soapy to the touch, and turn red litmus paper blue.
What is an Alkali?
An alkali is a specific type of base. An alkali is a base that is soluble in water. So, all alkalis are bases, but not all bases are alkalis. Think of it like this: all squares are rectangles, but not all rectangles are squares. Similarly, all alkalis are bases, but not all bases are alkalis.
Now, let’s talk about Calcium Oxide (CaO)
Calcium oxide, commonly known as quicklime, is a chemical compound with the formula CaO. It’s a white and solid substance.
When calcium oxide (CaO) reacts with water, it undergoes a vigorous reaction to form calcium hydroxide, Ca(OH)2:
CaO (s) + H2O (l) → Ca(OH)2 (aq)
This reaction is highly exothermic, meaning it releases a lot of heat.
Now, let’s look at the product, calcium hydroxide (Ca(OH)2). Calcium hydroxide is a strong base. While it’s not as soluble in water as some other strong bases like sodium hydroxide (NaOH) or potassium hydroxide (KOH), it does dissolve to a certain extent, producing hydroxide ions in the solution.
Because calcium oxide reacts with water to form a base (calcium hydroxide), calcium oxide itself is considered a basic oxide.
So, is CaO an alkali or a base?
Since CaO reacts with water to form Ca(OH)2, which is a base, CaO is definitely a base or we can say basic oxide.
Now, about it being an alkali: Calcium hydroxide, Ca(OH)2, is sparingly soluble in water. Since an alkali is a base that is soluble in water, Ca(OH)2 is often considered an alkali, though not as strong an alkali as NaOH or KOH due to its lower solubility.
However, when we talk about CaO itself, it’s more accurate to call it a basic oxide because it forms a base when it reacts with water. In many contexts, due to its ability to form a soluble base (to some extent), it’s also referred to as an alkaline substance or an alkali in a broader sense, especially when discussing its general properties and uses (like neutralising acids in soil or industrial processes).
Common Doubts of Chemistry:
