Name: China Manufacturer High Quality Potassium sodium tartrate tetrahydrate CAS 6381-59-5
Brand: Wuhan Fortuna Chemical Co., Ltd.

Potassium sodium tartrate tetrahydrate, commonly known as Rochelle salt, is a crystalline double salt with the chemical formula $KNaC4H4O6 \cdot4H2O$ . Below is a detailed chemical breakdown:

1. Chemical Structure & Formula

Molecular Formula: $C4H4KNaO6 \cdot4H2O$
Anhydrous Core: Potassium sodium tartrate ( $KNaC4H4O6).$
Derived from tartaric acid (HOOC−CH(OH)−CH(OH)−COOH)by replacing acidic hydrogens with $K +$ and Na.
Hydration: Contains 4 water molecules (4H2O) per formula unit, integrated into the crystal lattice via hydrogen bonding.
Stereochemistry: Uses the meso form of tartrate (optically inactive due to internal symmetry).

Structural Highlights:

Tartrate ion: -OOC−CH(OH)−CH(OH)−COO−
Cations: $K +$ and Na⁺ balance the charge.
Water molecules stabilize the crystal structure.

2. Key Properties

Property	Value/Description
Appearance	Colorless to blue-tinged translucent crystals
Molar Mass	282.22 g/mol (210.16 anhydrous + 72.06 for 4H₂O)
Solubility	Highly soluble in water (63 g/100 mL at 20°C); insoluble in ethanol.
Density	1.79 g/cm³
pH	~7–8 (mildly alkaline)
Decomposition	Loses water at 55–60°C; decomposes at 220°C.

3. Unique Characteristics

Piezoelectricity:
One of the first discovered piezoelectric crystals (generates electric charge under mechanical stress). Used in early microphones, phonograph pickups, and pressure sensors.
Ferroelectricity:
Exhibits ferroelectric properties below 24°C (Curie temperature).

4. Applications

Food Industry:
Emulsifier in baking powders (prevents premature reactions).
Stabilizer in jellies, margarine, and processed cheeses.
Analytical Chemistry:
Key component of Fehling's solution (tests for reducing sugars like glucose).
Used in Benedict's reagent for similar purposes.
Electronics:
Historical use in piezoelectric devices (e.g., crystal oscillators).
Medicine:
Laxative (rarely used today).
Electroplating:
Complexing agent in silvering mirrors and copper plating baths.

5. Synthesis

Produced by neutralizing tartaric acid with sodium carbonate and potassium hydroxide:

2 H2C4H4O6+Na2CO3→2 NaHC4H4O6+CO2+H2O
NaHCX4HX4OX6+KOH---->KNaCX4HX4OX6+HX2O
The solution is crystallized to form the tetrahydrate.

6. Safety & Handling

Non-toxic: GRAS (Generally Recognized As Safe) in food.
LD₅₀ (oral, rat): 4,000 mg/kg (low toxicity).
Precautions:
Dust may irritate eyes/respiratory tract.
Store in airtight containers (hygroscopic).

7. Why Tetrahydrate?

The four water molecules:

Stabilize the crystal lattice via H-bonding.
Enable piezoelectric/ferroelectric behavior by creating asymmetric structures.
Enhance solubility compared to anhydrous form.

Key Takeaway

Potassium sodium tartrate tetrahydrate is a versatile compound bridging food science, analytical chemistry, and materials physics. Its unique piezoelectricity revolutionized early electronics, while its role in Fehling's solution remains essential for sugar detection in labs. Despite being largely replaced in electronics by quartz/ceramics, it remains a staple in food and chemical applications.