Potassium Binoxalate: Properties, Uses & Lab Guide

Potassium binoxalate is a well-characterized, water-soluble potassium salt of hydrogen oxalate that serves as a reliable primary standard and buffer component across a wide range of analytical chemistry applications.

Chemical Name

Potassium hydrogen oxalate (Potassium binoxalate)

Molecular Formula

KHC2O4

Molecular Weight

128.13 g/mol

CAS Number

127-95-7

Appearance

White crystalline powder

Solubility

Soluble in water; slightly soluble in ethanol

Primary Use

Primary standard for permanganate titrations and pH buffer preparation

Chemical Identity and Physical Properties

Potassium binoxalate, systematic name potassium hydrogen oxalate, has the molecular formula KHC₂O₄ and a molecular weight of approximately 128.13 g/mol (CAS 127-95-7). It is the monopotassium salt of oxalic acid, retaining one acidic proton, which gives it both acidic character and strong reducing power toward oxidizing agents.

The compound appears as a white, odorless crystalline powder. It is readily soluble in water, producing mildly acidic solutions (approximate pH 2–3 at typical working concentrations), and is only slightly soluble in common organic solvents such as ethanol. Its melting point and precise solubility figures should be confirmed against the current certificate of analysis supplied with each lot.

Potassium binoxalate is stable under ambient conditions when stored in a cool, dry environment away from strong oxidizers and bases. Prolonged exposure to moisture or heat can lead to slow decomposition, so tightly sealed storage is recommended.

Laboratory Applications

Titrimetry and Standardization. Potassium binoxalate is widely used as a primary standard for standardizing potassium permanganate (KMnO₄) solutions. Because it can be obtained in high purity and has a well-defined stoichiometry, it allows accurate determination of KMnO₄ concentration in redox titrations. This is essential for subsequent analyses of iron, hydrogen peroxide, and other oxidizable analytes.

pH Buffer Preparation. Aqueous solutions of potassium binoxalate are used as reference pH buffers. A 0.05 mol/kg solution of potassium tetroxalate (the related KH₃(C₂O₄)₂·2H₂O) has historically been defined as a NIST/IUPAC primary pH standard, and potassium hydrogen oxalate solutions are employed at low pH (approximately 1.7–2.2) for electrode calibration in acidic ranges.

Analytical Chemistry and Synthesis. The compound serves as a source of oxalate ion in precipitation reactions (e.g., for rare-earth element separations), as a complexing agent, and as a reagent in certain organic synthesis protocols requiring controlled acidity and oxalate supply.

Calibration and Quality Control. High-purity lots of potassium binoxalate support method validation and instrument calibration routines where a well-characterized, stable acidic standard is required.

Safe Handling, Storage, and Disposal

Hazard Overview. Potassium binoxalate is harmful if swallowed, inhaled as dust, or absorbed through skin. Oxalate ions can precipitate calcium in biological systems, potentially causing hypocalcemia upon significant exposure. It is classified as irritating to the eyes, skin, and respiratory tract.

Personal Protective Equipment. Wear appropriate PPE when handling: chemical-resistant gloves, laboratory coat, and safety glasses or goggles. When weighing or handling fine powder, use a well-ventilated fume hood or appropriate dust mask to avoid inhalation.

Storage. Store in a tightly closed container in a cool (below 25 °C), dry, well-ventilated location, away from strong oxidizing agents, strong bases, and incompatible metals. Shelf life is typically multi-year when stored properly; verify with the lot-specific certificate of analysis.

Disposal. Dispose of solutions and solid waste in accordance with local, regional, and national regulations governing oxalate-containing chemical waste. Do not pour concentrated solutions down the drain without appropriate neutralization and verification of local discharge limits.

First Aid. In case of skin or eye contact, flush immediately with copious water for at least 15 minutes and seek medical attention if irritation persists. If ingested, seek immediate medical advice and show the product safety data sheet to the attending physician.

Preparation of Standard Solutions

Drying. Before use as a primary standard, potassium binoxalate should be dried to constant mass at approximately 105 °C for at least 1–2 hours to remove adsorbed moisture, then cooled in a desiccator. Verify the recommended drying conditions on the current lot certificate, as conditions can vary by application.

Weighing and Dissolution. Accurately weigh the required mass on an analytical balance to at least four decimal places. Transfer quantitatively to a volumetric flask and dissolve in freshly prepared, CO₂-free deionized water. Make up to volume at the calibration temperature (usually 20 °C or 25 °C) and mix thoroughly.

Concentration Calculation. Calculate the exact molarity using the accurately weighed mass and the lot-specific molecular weight. For permanganate standardization, use the stoichiometry of the redox reaction (two moles of KMnO₄ react with five moles of oxalate in acid solution) to derive the KMnO₄ concentration from the titre.

Stability of Solutions. Freshly prepared potassium binoxalate solutions are stable for several weeks when stored in a stoppered borosilicate glass vessel at room temperature and protected from light and biological contamination. Discard solutions showing visible turbidity or unusual color.

Quality, Purity Grades, and Procurement

Purity Considerations. For titrimetric and pH standardization work, reagent-grade or primary-standard-grade potassium binoxalate is required. Primary standard grades typically assay at ≥99.9% purity on a dry-weight basis, with strictly controlled levels of heavy metals, chloride, sulfate, and other common impurities.

Aladdin Scientific Supply. Aladdin Scientific offers potassium binoxalate (SKU P1508360) suitable for laboratory use. Customers should request the certificate of analysis for each lot to confirm purity, moisture content, and impurity profiles before use in critical assays.

Packaging and Quantity. The compound is typically available in various pack sizes to suit both routine laboratory use and larger-scale preparation. Consult the current product page or contact Aladdin Scientific's technical sales team for available quantities and pricing.

Regulatory and Documentation. A current Safety Data Sheet (SDS) conforming to GHS/REACH requirements is available for all shipments. Certificates of Analysis, HPLC purity traces, and other quality documents can be requested at the time of order or downloaded from the product page.

Frequently asked questions

What is potassium binoxalate used for in the laboratory?

Potassium binoxalate is primarily used as a primary standard for standardizing potassium permanganate solutions in redox titrimetry and for preparing acidic reference pH buffer solutions. It also serves as a source of oxalate ion in precipitation and separation procedures.

How should potassium binoxalate be stored to maintain its purity?

Store potassium binoxalate in a tightly sealed container in a cool (below 25 °C), dry, well-ventilated area, away from strong oxidizers, strong bases, and moisture. Always dry the reagent to constant mass before use as a primary standard.

Is potassium binoxalate hazardous, and what precautions are needed?

Yes, potassium binoxalate is harmful if ingested, inhaled as dust, or in contact with skin and eyes. Always wear chemical-resistant gloves, a lab coat, and eye protection. Handle powders in a fume hood to avoid inhalation, and follow local regulations for disposal of oxalate-containing waste.

What purity grade is required for use as a primary standard?

Primary standard applications require a minimum assay purity of ≥99.9% on a dry-weight basis, with certified low levels of key impurities such as heavy metals, chloride, and sulfate. Always verify purity against the lot-specific certificate of analysis before use.

Can potassium binoxalate solutions be prepared in advance and stored?

Yes, freshly prepared solutions are stable for several weeks when stored in a stoppered borosilicate glass container at room temperature, protected from light and biological contamination. Discard any solution that shows turbidity, unusual color, or signs of microbial growth.

References

1. IUPAC Recommendations on pH measurement and primary buffer standards, Pure and Applied Chemistry.
2. National Institute of Standards and Technology (NIST). Standard Reference Materials catalog — pH buffer standards.
3. Skoog, D. A.; West, D. M.; Holler, F. J.; Crouch, S. R. Fundamentals of Analytical Chemistry, 9th ed.; Cengage Learning: Mason, OH, 2014.
4. Safety Data Sheet: Potassium hydrogen oxalate (CAS 127-95-7). Aladdin Scientific.

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