Baking Soda (Sodium Bicarbonate)
- Chemical formula: (NaHCO_3)
- Commonly used as a leavening agent in baking.
- Acts as a mild abrasive in cleaning.
- Can neutralize acids; used as an antacid.
- Deodorizing properties; often placed in refrigerators to absorb odors.
Washing Soda (Sodium Carbonate)
- Chemical formula: (Na_2CO_3)
- Stronger base than baking soda.
- Often used as a stain remover in laundry.
- Can be used to strip paint or as a descaling agent.
- Used in making glass and as a water softener in laundry.
Sodium Hydroxide
- Chemical formula: (NaOH)
- Commonly known as lye or caustic soda.
- Highly caustic and can cause burns on skin.
- Used in soap making (saponification).
- Plays a role in many industrial processes, such as papermaking and chemical synthesis.
- Frequently used as a drain cleaner.
Plaster of Paris
- Chemical name: Calcium sulfate hemihydrate.
- Chemical formula: (CaSO_4·0.5H_2O)
- Commonly used for making casts and molds.
- When mixed with water, it rehydrates and sets to form a hard solid.
- Historically used in creating ornate decorative elements in architecture.
- Also used in fireproofing and as a surgical splinting material.
Water of crystallization (or water of hydration)
It refers to the specific number of water molecules present in one formula unit of a salt. This water is not present as liquid but is bound within the solid structure.
Plaster of Paris is the hemihydrate form of calcium sulfate, and its chemical formula is (CaSO_4·0.5H_2O). This means that for every one molecule of calcium sulfate, there is half a molecule of water of crystallization. This might sound a bit strange because you can’t really have “half” a molecule of water in a practical sense. Instead, it’s more accurate to say that for every two molecules of calcium sulfate, there’s one molecule of water.
When Plaster of Paris is mixed with water, it rehydrates to form gypsum, which is the dihydrate form of calcium sulfate ((CaSO_4·2H_2O)). In this process, the Plaster of Paris hardens or sets.
So, the “0.5” in the formula for Plaster of Paris refers to its water of crystallization.