Potassium biphthalate: structure, nomenclature, uses, risks

It is a stable, non-hygroscopic compound, which facilitates the preparation of the solution since it does not absorb water during the weighing process. It can be prepared by the reaction between phthalic acid and a KOH solution, in which a hydrogen in the phthalic acid molecule is replaced by a potassium atom.

Potassium biphthalate

Potassium biphthalate receives this name because there is a slightly acidic hydrogen in its molecule. This hydrogen is the one found in the -OH group that is right next to the carbonyl group, which is part of the carboxyl that does not react. These types of salts are known by the name of acid salts, as they are not totally neutral.

Chemical structure


6 H 4 COOHCOOK = C 8 H 5 KO 4


– Potassium biphthalate.

– Potassium acid phthalate.

– Potassium hydrogen phthalate.



1.636 g / mL.

Molar mass

204.22 g / mol.


Water and alcohol

Melting point

295 ° C with decomposition.


Crystalline solid to white.

Specific weight

1.64 gr / cm3.

Derivatographic study of potassium biphthalate

Derivatographic measurements have shown that the decomposition of potassium bipthalate begins between 190 ° C and 200 ° C, and the non-hygroscopic preparation can be prepared between 100 ° C and 150 ° C.

Enthalpy changes can also be obtained from the derivatogram, this produces information about the additional mechanism of thermal decomposition and changes of state of the sample.

Uses and applications

This compound is used in analytical chemistry in the titration or acid-base titration as a primary standard for standardization in the preparation of solutions of different compounds.

Standardization of a base (alkali = NaOH)

When preparing a solution of NaOH, it cannot be guaranteed that the concentration with which the solution remains is correct; This is due to the fact that NaOH is a very hygroscopic solid substance (it absorbs water from the air), and when it is weighed it is left with some moisture, which makes the amount of substance not the most optimal.

For this, a solution is prepared with potassium acid phthalate, which is a primary standard (due to its high stability); Add a few drops of phenolphthalein acid-base indicator and proceed to add the NaOH solution as titrant until a pink color remains present in the potassium acid phthalate solution.

With the data obtained, the pertinent calculations are carried out to find the real concentration of NaOH.

The following image illustrates the chemical reaction between potassium acid phthalate and sodium hydroxide.

Potassium biphthalate

As a buffer in pH determination

A buffer solution or buffer is one that is formed by both the acid and the acid salt, this makes it remain in such conditions that the pH value does not change when small amounts of acid or base are added.


– Exposure to fire. As with most organic solids, fire can occur at elevated temperatures or by contact with an ignition source.

– Fine dust dispersed in air in sufficient concentrations, and in the presence of an ignition source, is a potential for a dangerous dust explosion.

– It is a stable substance at room temperature and under adequate storage conditions. Avoid excessive heat and humidity.

– May be incompatible with strong oxidants such as nitric acid.

– Decomposition can form carbon oxides which are toxic.

Regarding health

– By accidental ingestion, it can cause vomiting, diarrhea and irritation of the membranes due to its acidity.

– By inhalation causes irritation in the respiratory tract and cough.

– Causes irritation on the skin.

– In the eyes it causes irritation, redness and pain.

– It is considered not a carcinogenic, teratogenic or mutagenic substance.

Emergency and first aid

– Rinse the eyes with plenty of water, remove contact lenses if wearing them and let the water run through the eyes without being touched with the hands.

– If there was contact with the skin, remove clothing and footwear, wash with plenty of water and wash the garments very well before using again.

– In case of ingestion, avoid inducing vomiting, give water to drink.

– In case of inhalation, take the person to breathe fresh air; in case of difficult breathing, supply oxygen.

– In all cases ask for urgent medical assistance.

– In case of leakage or spillage, collect the product in a clean container and try not to scatter the powder.

Personal protection measures

– Keep out of the place where drinks, food and feed (pet food) are stored.

– Use dust masks, neoprene or PVC gloves. Nitrile gloves are used today.

– Wear suitable clothing that covers most of the body, including boots or covered shoes and safety glasses.

– Local exhaust ventilation is recommended, with an air extractor system, taking into account the prevailing wind direction.

– The product is miscible in water, it does not absorb into the soil, it is not bioaccumulative or biodegradable, it is not expected to affect aquatic life. However, when disposing of it, it must be done with the help of specialized personnel: do not dispose of via drains.

– Store in orange / green area, cool dry and ventilated place, and separated from incompatible material.

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