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Potassium hydrogen phthalate (KHP), with the chemical formula \(\mathrm{KHC}_{8}\mathrm{H}_{4} \mathrm{O}_{4}\), is a crystalline, white solid commonly used in the laboratory as a primary standard for acid-base titrations. This compound contains a hydrogen phthalate ion \(\mathrm{HC}_{8}\mathrm{H}_{4}\mathrm{O}_{4}^{-}\) that takes part in reactions with bases. Here are some key characteristics of this compound:

• KHP is stable and non-hygroscopic, meaning it does not absorb moisture from the air, making it ideal for accurate mass measurements.
• It has a high purity, which is crucial for being a reliable standard.
• By dissolving a known mass of KHP in water, one can determine the concentration of basic solutions, such as NaOH, through titration.

In this exercise, \(0.902\text{ g}\) of KHP was dissolved in water to standardize a sodium hydroxide solution through titration.

Titration is a quantitative chemical analysis method used to determine the concentration of an unknown solution. The process involves gradually adding small volumes of a solution of known concentration, called the titrant, to the unknown solution until the chemical reaction is complete.
In this specific problem, sodium hydroxide (\(\mathrm{NaOH}\)) is used as the titrant to find its own concentration using potassium hydrogen phthalate (KHP) as the analyte.

• The goal is to reach the equivalence point, the stage at which the amount of titrant is chemically equivalent to the amount of analyte in the solution.
• Indicators, or pH meters, are often employed to detect this point.

The process in question reached the equivalence point when \(26.45\text{ mL}\) of \(\mathrm{NaOH}\) was added, indicating the consumed moles of hydroxide ions corresponded to those of KHP.

In chemical reactions, particularly in titrations, it's often helpful to simplify the equation to show only the species that actually change during the process. This simplification is captured by a net ionic equation. For the standardization of sodium hydroxide with potassium hydrogen phthalate, the net ionic equation is: \[ \mathrm{HC}_{8}\mathrm{H}_{4}\mathrm{O}_{4}^{-}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \rightarrow \mathrm{C}_{8}\mathrm{H}_{4}\mathrm{O}_{4}^{2-}(\mathrm{aq})+\mathrm{H}_{2}\mathrm{O}(\ell) \] This equation demonstrates that the hydrogen phthalate ion (\(\mathrm{HC}_{8}\mathrm{H}_{4}\mathrm{O}_{4}^{-}\)) reacts with hydroxide ions (\(\mathrm{OH}^{-}\)) to form phthalate ions (\(\mathrm{C}_{8}\mathrm{H}_{4}\mathrm{O}_{4}^{2-}\)) and water.
Using net ionic equations helps focus on the actual chemical changes and can simplify stoichiometric calculations.

Determining the molarity or molar concentration of a solution is a critical skill in chemistry. The molarity is defined as the number of moles of solute divided by the volume of solution in liters.
In this exercise, we calculated the molarity of the \(\mathrm{NaOH}\) solution used in a titration process. Here's how it unfolds:

• First, find out the moles of potassium hydrogen phthalate dissolved. Given its molar mass is \(204.22 \text{ g/mol}\), and \(0.902 \text{ g}\) is used, the moles of KHP are \(0.004418 \text{ mol}\).
• The problem then uses stoichiometry to show that these moles of KHP equal the moles of \(\mathrm{OH}^{-}\) needed at the equivalence point.
• With \(26.45\text{ mL}\) of \(\mathrm{NaOH}\) solution required, converted into liters (\(0.02645 \text{ L}\)), the molarity becomes \(\frac{0.004418 \text{ mol}}{0.02645 \text{ L}} = 0.167 \text{ M}\).

This calculation provides the molar concentration of the sodium hydroxide, essential for stoichiometric and analytical purposes.