Potassium Binoxalate: Preparation, Handling & Lab Protocol

Potassium binoxalate is a well-characterized, stable acid salt of oxalic acid that serves as a reliable primary standard and buffer component in analytical and research laboratory workflows.

Chemical Name

Potassium binoxalate (Potassium hydrogen oxalate)

Molecular Formula

KHC2O4

CAS Number

127-95-7

SKU

P1508360

Primary Use

Primary standard in acid-base titrations and pH buffer calibration

Physical Form

White crystalline powder

Solubility

Soluble in water

Overview and Chemical Properties

Potassium binoxalate, also known as potassium hydrogen oxalate, has the molecular formula KHC₂O₄ and CAS number 127-95-7. It is the monopotassium salt of oxalic acid and appears as a white, odorless crystalline powder at room temperature. The compound is moderately soluble in water and produces an acidic solution due to the presence of the free carboxylic acid group. Its well-defined stoichiometry and high purity make it suitable as a primary standard in titrimetric analysis. Potassium binoxalate is also used to prepare pH 1.679 reference buffer solutions (at 25 °C) according to established metrological standards, providing a reliable reference point for pH meter calibration.

The compound should be stored in a cool, dry environment away from strong oxidizing agents. It has a defined molecular weight of approximately 128.13 g/mol, enabling precise gravimetric preparation of standard solutions.

Safety and Handling Precautions

Potassium binoxalate is an irritant and should be handled with appropriate personal protective equipment (PPE), including nitrile gloves, safety goggles, and a laboratory coat. Inhalation of dust should be avoided; work in a well-ventilated area or under a fume hood when handling powdered material in quantity.

As an oxalate salt, ingestion or significant dermal absorption may cause systemic toxicity through chelation of calcium ions. In case of skin or eye contact, flush immediately with copious amounts of water for at least 15 minutes and seek medical attention if irritation persists. Refer to the Safety Data Sheet (SDS) provided by Aladdin Scientific for complete hazard classifications, first-aid measures, and disposal requirements before use.

Dispose of potassium binoxalate solutions in accordance with local regulations governing oxalate-containing waste. Do not pour concentrated solutions down the drain without neutralization and appropriate treatment.

Solution Preparation Protocol

Materials required: Potassium binoxalate (P1508360, Aladdin Scientific), analytical balance (0.0001 g readability), volumetric flask (appropriate volume), Type 1 (ultrapure) water, glass stirring rod, and drying oven.

Drying: Prior to weighing, dry potassium binoxalate at 105 °C for 1–2 hours in an oven to remove residual moisture. Allow to cool in a desiccator to room temperature before use.

Weighing and dissolution:
1. Accurately weigh the required mass of dried potassium binoxalate on a calibrated analytical balance.
2. Transfer quantitatively to a clean volumetric flask.
3. Add approximately two-thirds of the required volume of ultrapure water and stir gently until completely dissolved.
4. Make up to the calibration mark with ultrapure water at the target temperature (typically 20–25 °C).
5. Invert the stoppered flask several times to ensure homogeneity.

Storage: Store prepared solutions in a tightly sealed borosilicate glass or HDPE container, labeled with concentration, preparation date, and preparer's initials. Solutions are generally stable for several weeks at 4 °C; discard if turbidity or visible contamination is observed.

Applications in Analytical Chemistry

Primary standard in titrimetry: Due to its high purity, defined molecular weight, and stability, potassium binoxalate is employed as a primary standard for standardizing base solutions (e.g., sodium hydroxide) in acid-base titrimetry. Its well-characterized acidic proton allows for precise equivalence-point determinations.

pH buffer and calibration reference: Aqueous solutions of potassium binoxalate at defined concentrations (commonly 0.05 mol/kg) provide a recognized reference buffer near pH 1.68 at 25 °C, useful for calibrating pH electrodes at low pH values and validating pH meter linearity.

Synthesis and intermediate use: The compound is used in organic and inorganic synthesis as a source of oxalate anions under mildly acidic conditions, and in formulation of specialty cleaning agents, fabric treatments, and wood-bleaching preparations where a controlled acidic oxalate environment is required.

Gravimetric analysis: As a source of oxalate, it can be used to precipitate metal ions (e.g., calcium, rare earths) as insoluble oxalates for gravimetric determination.

Frequently asked questions

What is potassium binoxalate used for in the laboratory?

Potassium binoxalate is primarily used as a primary standard in acid-base titrimetry to standardize base solutions such as sodium hydroxide. It is also used to prepare low-pH reference buffer solutions for pH electrode calibration, as an oxalate source in gravimetric analysis, and in specialty synthesis and cleaning formulations requiring a mildly acidic oxalate environment.

How should potassium binoxalate be stored to maintain its integrity?

Potassium binoxalate should be stored in a tightly sealed container in a cool, dry location away from strong oxidizing agents and moisture. It should be dried at 105 °C before use as a primary standard to ensure accurate mass-based calculations. Prepared aqueous solutions should be stored at 4 °C in sealed borosilicate glass or HDPE containers and used within a few weeks.

Is potassium binoxalate hazardous, and what PPE is required?

Yes, potassium binoxalate is classified as an irritant and can be systemically toxic upon ingestion or significant dermal absorption due to its oxalate content, which chelates calcium ions. Users should wear nitrile gloves, safety goggles, and a laboratory coat when handling this compound. Work should be conducted in a well-ventilated area or under a fume hood, and the full Safety Data Sheet (SDS) should be consulted before use.

What concentration of potassium binoxalate is used for pH buffer preparation?

A molality of 0.05 mol/kg of potassium binoxalate in ultrapure water is commonly used to prepare a reference buffer with an assigned pH of approximately 1.679 at 25 °C. This standard is recognized in metrological guidelines for pH electrode calibration at low pH values.

Can potassium binoxalate be used to precipitate metal ions?

Yes, potassium binoxalate serves as a convenient source of oxalate anions in mildly acidic aqueous solution and can be used to precipitate metal ions such as calcium or rare-earth elements as their insoluble oxalate salts. These precipitates can then be collected, dried, and weighed for gravimetric determination or further processed.

References

1. Bates, R.G. (1973). Determination of pH: Theory and Practice. 2nd ed. Wiley. (Reference for potassium hydrogen oxalate pH 1.679 buffer standard.)
2. IUPAC Recommendations on pH measurement and buffer standards (various years). Pure and Applied Chemistry.
3. National Institute of Standards and Technology (NIST). Standard Reference Materials for pH measurement. Gaithersburg, MD.

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