quicklime
Calcium oxide is a white powdery solid. It can be made by heating calcium carbonate.
It can absorb water. It has a water absorption capacity. It can absorb water from liquids in some organic syntheses. The calcium hydroxide becomes a paste and settles at the bottom of the container. If excess calcium oxide is added later, it stays as a powder. This demonstrates that the water has fully absorbed.
Hydrated lime/Slaked lime
Calcium hydroxide is a white, powdery solid. You can make it by adding water to calcium oxide. This makes the paste solid, “lime milk” (to be mentioned below). Then, you dry and crush it.
The reaction of calcium oxide and water creates a lot of heat. This reaction can even cause the unreacted water to boil, causing the lime to appear “cooked. Many self-heating hot pots and self-heating cans also use this reaction to heat.
limestone
Calcium carbonate is a white, hard solid. It is a naturally occurring mineral. It can also be made by reacting calcium hydroxide with carbon dioxide. It quickly reacts to acid to produce calcium ions and carbon dioxide. These can be used to test acid.
Milk of lime
It is a paste-like solid or fluid. You make it by adding a little water to calcium hydroxide. Limewater is a clear solution. It is made by adding a lot of water to calcium hydroxide.
Calcium hydroxide is not very soluble in water. Water can fully enter undissolved calcium hydroxide. So, mix calcium hydroxide with water. Depending on the amount of water used, you get a paste, fluid, suspension, or a solution. The first three are a mix of calcium hydroxide solution and dissolved solids. To get a clear solution, you need a lot of water. Otherwise, filter the suspension.
Paste-like lime milk can be used for wall painting and caulking during construction. After being applied, it absorbs carbon dioxide from the air. Then, calcium carbonate becomes hard. Lime water is saturated with it. It is a reagent used to detect carbon dioxide in experiments.
Also, although calcium hydroxide has low solubility, it is a strong base. The part that fully dissolves ionizes. Calcium hydroxide is not toxic and won’t pollute the environment. But it can irritate and corrodes the human body.
Soda lime
It is a mixture of calcium oxide and sodium hydroxide. It is a powder or granular solid. It may contain a small amount of water and appear in a blocky form.
Usually used as a gas desiccant or to absorb acidic gases. Pure sodium hydroxide can quickly absorb water vapor. But, water will stick to its surface to form a saturated solution. This will prevent more water from being absorbed. Calcium oxide can absorb water droplets. This significantly enhances its total water absorption capacity. So, mixing calcium oxide with sodium hydroxide dries better than using either alone.