Potassium Binoxalate: Handling, Preparation & Lab Protocol

Potassium binoxalate is a mildly acidic potassium salt of oxalic acid (KHC2O4) widely used in analytical chemistry as a pH buffer component, a primary standard for alkalimetry, and a reference reagent for calibrating titrimetric systems.

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

SKU (Aladdin)

P1508360

Overview and Chemical Properties

Potassium binoxalate (KHC2O4, CAS 127-95-7) is the monopotassium salt of oxalic acid. It exists as a white, odorless crystalline solid with a molecular weight of 128.13 g/mol. The compound is mildly acidic due to the presence of one free carboxylic proton, which confers buffering capacity in the approximate pH range of 3–4 when used in appropriate concentrations.

Its high purity, defined stoichiometry, and stability under normal laboratory conditions make it suitable for use as a primary standard in alkalimetry. Potassium binoxalate is distinguishable from potassium tetroxalate (KHC2O4·H2C2O4·2H2O), which contains an additional molecule of free oxalic acid; researchers should confirm the exact form required for their specific application before use.

The compound is moderately soluble in water and only slightly soluble in ethanol. Aqueous solutions are acidic and should be handled with appropriate precautions.

Safety and Handling Guidelines

Potassium binoxalate is an oxalate salt and should be treated as a mild irritant and low-to-moderate toxicity compound. Oxalate anions can chelate calcium ions and may cause hypocalcemia upon significant systemic exposure. The following precautions are recommended:

• Personal Protective Equipment (PPE): Wear nitrile gloves, safety spectacles, and a laboratory coat at all times when handling the solid or its solutions.
• Inhalation: Avoid generating or inhaling dust. Work in a well-ventilated area or under a fume hood when weighing powders.
• Ingestion: The compound is toxic if ingested in significant quantities. Do not eat, drink, or smoke in the laboratory while handling this reagent.
• Skin and Eye Contact: Rinse affected areas immediately with copious water for at least 15 minutes and seek medical advice if irritation persists.
• Waste Disposal: Dispose of oxalate-containing waste in accordance with local regulations for mildly toxic chemical waste. Do not pour concentrated solutions down the drain without neutralization and appropriate dilution.

Consult the Safety Data Sheet (SDS) for Aladdin product P1508360 for complete hazard information before beginning any experiment.

Solution Preparation Protocol

The following protocol describes the preparation of a standard 0.05 mol/L potassium binoxalate solution suitable for use as a pH reference buffer or titrimetric standard.

Materials Required

• Potassium binoxalate (Aladdin P1508360), reagent-grade or higher
• Freshly boiled and cooled ultrapure or distilled water (Type 1 or equivalent)
• Analytical balance (readability ≤ 0.1 mg)
• Volumetric flask (100 mL or 1000 mL, Class A)
• Magnetic stirrer and stir bar
• pH meter (calibrated) for verification

Procedure

1. Drying: If high-accuracy standardization is required, dry potassium binoxalate at 60 °C for 1 hour and allow to cool in a desiccator over silica gel before weighing. Do not exceed 60 °C, as decomposition may occur at elevated temperatures.
2. Weighing: Accurately weigh the required mass on a calibrated analytical balance. For a 0.05 mol/L solution in 1000 mL, weigh 6.407 g (0.05 mol × 128.13 g/mol).
3. Dissolution: Transfer the weighed solid to a clean beaker. Add approximately 800 mL of ultrapure water and stir with a magnetic stirrer until completely dissolved. The dissolution rate may be slow at room temperature; gentle warming to 40 °C may be applied if needed.
4. Transfer and Make-Up to Volume: Quantitatively transfer the solution to a 1000 mL Class A volumetric flask. Rinse the beaker three times with small volumes of ultrapure water, adding the rinsings to the flask. Allow the solution to equilibrate to room temperature (20–25 °C), then make up to the mark with ultrapure water and mix by inversion (at least 10 times).
5. Verification: Measure the pH of the prepared solution using a calibrated pH meter. A 0.05 mol/L solution should register approximately pH 3.56–3.60 at 25 °C. Note that pH is temperature-dependent; record the measurement temperature.
6. Storage: Store in a tightly sealed borosilicate glass or high-density polyethylene (HDPE) bottle, labeled with compound name, concentration, preparation date, and preparer's initials. Stable for up to 3 months when stored at 2–8 °C and protected from light.

Analytical Applications

Potassium binoxalate has several established uses in analytical and research laboratories:

• pH Buffer Reference Standard: A 0.05 mol/L aqueous solution of potassium binoxalate provides a reproducible pH of approximately 3.557 at 25 °C according to NIST/ISO reference buffer specifications. It is routinely used to calibrate pH meters in the acidic range alongside other primary buffer standards.
• Primary Standard for Alkalimetry: Because potassium binoxalate can be obtained in high purity and has a stable, well-defined equivalent weight (128.13 g/eq), it can serve as a primary standard for standardizing sodium hydroxide and other base solutions. The monobasic reaction with NaOH proceeds as: KHC2O4 + NaOH → KNaC2O4 + H2O.
• Permanganate Titration Calibration: In combination with other oxalate-based reagents, potassium binoxalate is used in calibrating potassium permanganate (KMnO4) solutions, exploiting the quantitative oxidation of oxalate by permanganate under acidic conditions.
• Textile and Industrial Reference: Potassium binoxalate has historical use in fabric stain removal and as a mordant; however, in the research context its analytical role is primary.

Researchers should verify that the purity and grade of the Aladdin P1508360 product meet the requirements of their specific application, particularly when used as a primary standard where assay ≥ 99.5% is typically required.

Troubleshooting and Quality Checks

Use the following checklist to diagnose common issues encountered when working with potassium binoxalate solutions:

Symptom	Likely Cause	Corrective Action
pH reading higher than expected (~3.6 at 25 °C)	Partial decomposition, contamination with carbonate, or calibration error	Recalibrate pH meter with fresh buffer standards; prepare a fresh solution from dried reagent
Incomplete dissolution	Temperature too low or insufficient mixing time	Warm solution gently to 40 °C with stirring; do not boil
Cloudy solution	Presence of insoluble impurities or microbial growth (aged solutions)	Discard and prepare fresh solution; check reagent expiry and storage conditions
Titration endpoint drift	CO2 absorption into NaOH standard or degraded potassium binoxalate	Use freshly boiled and cooled water; re-standardize the base solution
Balance reading unstable during weighing	Hygroscopic moisture uptake or electrostatic charge on powder	Dry reagent at 60 °C for 1 h and weigh promptly; use anti-static weighing vessels

Always document lot numbers, preparation dates, and verification pH readings in the laboratory notebook for traceability and compliance purposes.

Frequently asked questions

What is the difference between potassium binoxalate and potassium tetroxalate?

Potassium binoxalate (KHC2O4) contains one potassium ion and one hydrogen oxalate anion, giving a molecular weight of 128.13 g/mol. Potassium tetroxalate (KHC2O4·H2C2O4·2H2O) additionally contains one molecule of free oxalic acid and two waters of crystallization, resulting in a higher molecular weight and a lower pH buffer point (~1.68 at 25 °C). Always confirm which salt is specified in your method before ordering or preparing solutions.

How should potassium binoxalate be stored to maintain its purity?

Store potassium binoxalate in a tightly closed container in a cool (15–25 °C), dry, and well-ventilated area, away from oxidizing agents and strong bases. Protect from moisture and direct light. When used as a primary standard, dry the material at 60 °C for 1 hour before use and store the dried reagent in a desiccator over silica gel until needed.

Can potassium binoxalate be used to calibrate a pH meter?

Yes. A 0.05 mol/L aqueous solution of potassium binoxalate is recognized as a primary pH reference buffer by NIST and equivalent standards bodies, with an assigned pH of approximately 3.557 at 25 °C. It is particularly useful for calibrating pH meters in the acidic range (pH 3–4). Ensure the solution is freshly prepared from dried, high-purity reagent and that the pH meter is also calibrated at the measurement temperature.

Is potassium binoxalate hazardous, and what first-aid measures apply?

Potassium binoxalate is classified as harmful if ingested or inhaled in significant amounts, primarily due to the oxalate anion's ability to chelate calcium. For skin or eye contact, flush immediately with large amounts of water for at least 15 minutes and seek medical attention if irritation persists. If ingested, do not induce vomiting; seek immediate medical advice and show the SDS to the attending physician. Always consult the current SDS for product P1508360 before use.

References

1. Bates, R.G. (1973). Determination of pH: Theory and Practice, 2nd ed. Wiley, New York. [Reference for primary pH buffer standards including potassium hydrogen oxalate]
2. NIST Standard Reference Database. Primary pH Standard Buffer Values. National Institute of Standards and Technology.
3. Skoog, D.A., West, D.M., Holler, F.J., Crouch, S.R. (2014). Fundamentals of Analytical Chemistry, 9th ed. Cengage Learning.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.