Lime water doesn't react with water, because lime water is already a solution of calcium hydroxide (slaked lime) in water. The question is misleading. However, quicklime (calcium oxide) does react with water. The reaction between quicklime and water produces slaked lime (calcium hydroxide) and heat.
Here's a breakdown of what actually happens:
Quicklime (Calcium Oxide) Reacts with Water
The substance typically referred to when discussing a reaction with water is actually quicklime, or calcium oxide (CaO). Lime water itself is a product of a reaction involving water.
- Reactants: Calcium oxide (CaO, quicklime) and Water (H₂O)
- Product: Calcium hydroxide (Ca(OH)₂, slaked lime). When dissolved in water, this is called lime water.
The Reaction
The reaction between quicklime and water is an exothermic reaction, meaning it releases heat. This is represented by the following chemical equation:
CaO (s) + H₂O (l) → Ca(OH)₂ (aq) + Heat
Observations
- Heat Generation: The mixture will become warm.
- Formation of Slaked Lime: A white powder (calcium hydroxide) will form.
- Lime Water Creation (if excess water is used): If sufficient water is present, some of the calcium hydroxide will dissolve, creating a solution known as lime water.
Lime Water and Carbon Dioxide
It is important to note that lime water itself is commonly used to test for the presence of carbon dioxide. When carbon dioxide is bubbled through lime water, it reacts to form calcium carbonate, which is insoluble and causes the lime water to turn milky. This is a separate reaction from the reaction between quicklime and water.
Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l)
