Chemical Formula: Potassium Hydrogen Phthalate
Potassium Hydrogen Phthalate, commonly known as KHP, is an important chemical compound used in analytical chemistry, laboratory standardization, and acid-base titration. Its chemical formula is C8H5KO4. KHP is particularly useful because it is a stable, solid compound with a well-defined composition, making it a popular primary standard for determining the exact concentration of sodium hydroxide and other alkaline solutions.
Understanding the KHP chemical formula is useful for calculating its molar mass, preparing standard solutions, and performing accurate titration calculations. This article explains the formula, chemical structure, molar mass, properties, and common laboratory applications of potassium hydrogen phthalate, along with practical calculation examples.
KHP at a Glance
| Property | Value |
|---|---|
| Chemical name | Potassium hydrogen phthalate |
| Abbreviation | KHP |
| Chemical formula | C8H5KO4 |
| Molar mass | 204.22 g/mol |
| CAS number | 877-24-7 |
| Type | Acidic potassium salt |
| Acidic protons | 1 |
| Common use | Primary standard for acid-base titration |
What Is the Chemical Formula of KHP?
The chemical formula of potassium hydrogen phthalate is:
C8H5KO4
The abbreviation KHP comes from the compound's full name, potassium hydrogen phthalate. KHP is the monopotassium salt of phthalic acid and contains one acidic proton that can be neutralized by a strong base such as sodium hydroxide (NaOH). This acidic proton allows KHP to react with strong bases in a predictable 1:1 molar ratio, which is why KHP is widely used as a primary standard in acid-base titration.
KHP Chemical Formula and Molecular Composition
The formula C8H5KO4 indicates that one formula unit of potassium hydrogen phthalate contains:
- 8 carbon atoms (C)
- 5 hydrogen atoms (H)
- 1 potassium atom (K)
- 4 oxygen atoms (O)
KHP has a molar mass of approximately 204.22 g/mol. This value is especially important when weighing KHP for laboratory experiments because the number of moles can be calculated directly from its mass.
Calculating the Molar Mass of KHP
The molar mass can be calculated by adding the atomic masses of all elements in the formula:
C8H5KO4 = (8 × 12.011) + (5 × 1.008) + (1 × 39.098) + (4 × 15.999)
This gives approximately:
204.22 g/mol
Therefore, one mole of KHP has a mass of approximately 204.22 grams.
Why Is KHP Used as a Primary Standard?
KHP is one of the most commonly used primary standards in analytical chemistry. A primary standard should have characteristics that allow chemists to prepare solutions and perform quantitative measurements with high accuracy. Understanding the properties of related chemical compounds, such as Hydrogen Acetate, can also be useful when comparing different substances used in chemical analysis.
KHP is useful as a primary standard because it is relatively pure, stable under normal storage conditions, has a relatively high molar mass, and can be weighed accurately. It also reacts with sodium hydroxide in a predictable 1:1 molar ratio.
The reaction between KHP and sodium hydroxide can be represented as:
C8H5KO4 + NaOH → C8H4KNaO4 + H2O
In this reaction, one mole of KHP reacts with one mole of NaOH. This simple stoichiometric relationship makes KHP particularly convenient for standardizing sodium hydroxide solutions.
Example: Standardizing NaOH with KHP
Suppose a laboratory technician weighs 0.5105 g of KHP and dissolves it in distilled water. The solution is then titrated with a sodium hydroxide solution. The titration requires 25.00 mL of NaOH to reach the endpoint.
First, calculate the number of moles of KHP:
where m is the mass and M is the molar mass.
Therefore:
Because KHP and NaOH react in a 1:1 ratio:
The NaOH concentration is then:
Thus, the actual concentration of the NaOH solution is approximately 0.1000 M.
KHP in Acid-Base Titration
During a titration, KHP acts as a weak monoprotic acid. Although KHP is not a strong acid, its acidic hydrogen reacts quantitatively with strong bases such as NaOH.
The simplified net ionic reaction can be written as:
Here, the hydrogen phthalate ion donates its acidic proton to hydroxide, producing water and the phthalate ion.
Phenolphthalein is commonly used as an indicator in KHP-NaOH titrations. The endpoint occurs when a slight excess of NaOH causes the indicator to develop a persistent pale pink color.
Physical and Chemical Properties of KHP
Potassium hydrogen phthalate is commonly encountered as a white crystalline solid. It is generally supplied in a high-purity form for analytical applications. Like other laboratory chemicals, including Hydrogen Peroxide, its handling and use depend on its specific chemical properties and intended application.
- Appearance: White crystalline solid
- Acid-base behavior: Weak monoprotic acid
- Solubility: Soluble in water
- Analytical use: Primary standard for standardizing basic solutions
How Much KHP Is Needed for a Titration?
The required mass of KHP depends on the expected concentration of the base and the desired titration volume. The general calculation starts with:
where m is the required mass of KHP, M is the concentration of NaOH, V is the expected volume of NaOH in liters, and Mr is the molar mass of KHP.
For example, if a chemist expects to use 25.00 mL of approximately 0.100 M NaOH:
The result is approximately 0.5106 g of KHP. This is a convenient sample size because it produces a measurable titration volume without requiring an excessively large quantity of standard material.
KHP vs. Phthalic Acid
KHP should not be confused with phthalic acid. Phthalic acid has the molecular formula C8H6O4, while potassium hydrogen phthalate has the formula C8H5KO4.
The difference is related to the replacement of one acidic hydrogen in phthalic acid by a potassium ion. As a result, KHP is an ionic potassium salt rather than the original diprotic acid.
Why KHP Is Important in Analytical Chemistry
The importance of KHP comes from its combination of chemical stability, predictable stoichiometry, and accurate weighing characteristics. When preparing or standardizing a sodium hydroxide solution, the exact concentration of the base cannot always be assumed simply from the amount originally used to prepare it.
Standardization with KHP provides an experimental value for the actual concentration of the NaOH solution. That standardized solution can then be used for other quantitative analyses, including determining the concentration of unknown acidic samples.
KHP Chemical Formula: Frequently Asked Questions
What Is the Chemical Formula of KHP?
The chemical formula of potassium hydrogen phthalate (KHP) is C8H5KO4. KHP is commonly used as a primary standard in acid-base titrations, especially for standardizing sodium hydroxide solutions.
What Is the Molar Mass of KHP?
The molar mass of KHP is approximately 204.22 g/mol. This value is calculated from the atomic masses of carbon, hydrogen, potassium, and oxygen present in the C8H5KO4 formula.
What Does KHP Stand For in Chemistry?
KHP stands for potassium hydrogen phthalate. It is a potassium salt of hydrogen phthalate and is widely used in analytical chemistry because of its stability and well-defined composition.
Why Is KHP Used as a Primary Standard?
KHP is used as a primary standard because it is available in high purity, has a relatively high molar mass, is stable under normal laboratory conditions, and can be accurately weighed. These properties make it suitable for determining the exact concentration of standard solutions.
What Is the Reaction Between KHP and NaOH?
KHP reacts with sodium hydroxide (NaOH) in a 1:1 molar ratio. The acidic hydrogen in KHP reacts with hydroxide ions to form water, while the remaining phthalate species forms the corresponding salt.
KHP + NaOH → potassium sodium phthalate + H2O
How Do You Calculate the Moles of KHP?
The number of moles of KHP can be calculated by dividing its mass by its molar mass:
For example, if 0.5105 g of KHP is used:
Therefore, 0.5105 g of KHP contains approximately 0.002500 mol.
What Is KHP Used For in the Laboratory?
KHP is primarily used to standardize sodium hydroxide and other basic solutions. It is also useful in analytical chemistry experiments involving acid-base titration, concentration calculations, and quantitative analysis.
KHP Chemical Formula: Key Takeaways
The KHP chemical formula is C8H5KO4, and its molar mass is approximately 204.22 g/mol. Potassium hydrogen phthalate is widely used as a primary standard because it is stable, can be accurately weighed, and reacts with NaOH in a simple 1:1 molar ratio.
For students, laboratory technicians, and analytical chemists, understanding the formula of KHP is essential for calculating molar mass, preparing samples, and performing acid-base titrations. The combination of a well-defined chemical formula and reliable reaction stoichiometry makes KHP one of the most useful reference substances in quantitative chemical analysis.
KHP Chemical Formula References and Further Reading
If you want to explore more information about the KHP chemical formula, potassium hydrogen phthalate, molar mass, and its use in analytical chemistry, the following references provide additional scientific information:
- Potassium Hydrogen Phthalate – PubChem: View the PubChem KHP chemical information. This reference provides the molecular formula C8H5KO4, molecular weight, chemical identifiers, and structural information.
- Potassium Hydrogen Phthalate – NIST Chemistry WebBook: View the NIST Chemistry WebBook entry. NIST provides the chemical formula, molecular weight, CAS Registry Number, and other standardized information for potassium hydrogen phthalate.
- Potassium Hydrogen Phthalate – Wikipedia: Read more about potassium hydrogen phthalate. This page provides an overview of KHP, including its chemical formula, molar mass, properties, and common laboratory applications.
- Acid-Base Titrations – Chemistry LibreTexts: Learn about acid-base titration and standardization. This resource explains acid-base titration, standardization, and related analytical chemistry concepts.
- Acid-Base Titration – Chemistry LibreTexts: Study acid-base titration principles and calculations. This resource covers titration calculations, equivalence points, indicators, and the fundamentals of quantitative acid-base analysis.
These references can help readers verify the KHP chemical formula (C8H5KO4), its molar mass of approximately 204.22 g/mol, and its role in analytical chemistry and acid-base titration.
Natsume Cigem writes about chemistry, science, and laboratory topics, with a focus on making technical subjects easier to understand. The articles cover chemical formulas, properties of compounds, analytical chemistry, and practical calculation examples using information from reliable scientific sources.
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