Question

Potassium hydrogen phthalate (abbreviated as KHP) has the molecular formula \(\mathrm{KHC}_{8} \mathrm{H}_{4} \mathrm{O}_{4}\) and a molar mass of \(204.22 \mathrm{~g} / \mathrm{mol}\). KHP has one acidic hydrogen. A solid sample of KHP is dissolved in \(50 \mathrm{~mL}\) of water and titrated to the equivalence point with \(22.90 \mathrm{~mL}\) of a \(0.5010 \mathrm{M}\) NaOH solution. How many grams of KHP were used in the titration?

Short answer

2.344 g of KHP were used in the titration.

Step-by-step solution

Write the Balanced Reaction Equation

In a titration involving KHP and NaOH, the balanced chemical equation is: \( \text{KHP (aq) + NaOH (aq)} \rightarrow \text{KNaP (aq) + H}_2\text{O (l)} \). Here, 1 mole of KHP reacts with 1 mole of NaOH.

Calculate Moles of NaOH Used

Use the formula: \( \text{moles of NaOH} = \text{Volume (in L)} \times \text{Molarity} \). Substituting the given values, we have: \( 0.02290 \text{ L} \times 0.5010 \text{ mol/L} = 0.011479 \text{ mol NaOH} \).

Determine Moles of KHP

From the balanced chemical equation, 1 mole of KHP is required to react with 1 mole of NaOH. Hence, the moles of KHP used are equal to the moles of NaOH. Therefore, moles of KHP = 0.011479 mol.

Calculate Mass of KHP

Use the formula: \( \text{mass of KHP} = \text{moles} \times \text{molar mass} \). Substituting the given values: \( 0.011479 \text{ mol} \times 204.22 \text{ g/mol} = 2.344 \text{ g} \).

Key concepts

Molarity

Molarity is a way to express the concentration of a solution. It is specifically defined as the number of moles of solute per liter of solution, which can be written as: \[ \text{Molarity} (M) = \frac{\text{moles of solute}}{\text{liters of solution}} \]

• The solute is the substance being dissolved, while the solvent is the substance that does the dissolving. In most titrations, water is the solvent.
• In our case, NaOH is the solute in the titration process.

When performing a titration, knowing the molarity is crucial to calculate how many moles of reactant are present. This helps in determining the amount needed to reach the equivalence point—where the number of moles of acid equals the number of moles of base.

Balanced Chemical Equation

A balanced chemical equation is essential in stoichiometry as it ensures that the law of conservation of mass is adhered to. It shows the relationship between the reactants and the products in a chemical reaction.In our titration exercise, the reaction between KHP and NaOH can be represented as: \[ \text{KHP (aq) + NaOH (aq)} \rightarrow \text{KNaP (aq) + H}_2\text{O (l)} \]

• This equation is balanced because it shows that one mole of KHP reacts with one mole of NaOH, forming one mole of KNaP and one mole of water.
• Balanced equations allow us to understand the stoichiometric relationships, predicting the amount of product formed or reactant needed.

Thus, the balanced equation is fundamental to solve how many grams of the substance were used.

Molar Mass

Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It connects the number of moles and the mass of a substance, via this formula:\[ \text{Mass} = \text{Moles} \times \text{Molar Mass} \]For Potassium Hydrogen Phthalate (KHP), the molar mass is 204.22 g/mol.

• Knowing the molar mass is essential in converting moles to mass, which you often need to know when weighing out a substance.
• In the titration we discussed, once the moles of KHP are known, you can easily find the mass by multiplying by the molar mass.

This calculation is vital for experiments where precise measurements of reactants are necessary.

Stoichiometry

Stoichiometry refers to the calculations of reactants and products in chemical reactions. It is based on the balanced chemical equations and the mole concept. In a titration, stoichiometry allows us to track the exact proportions in which the reactants react. It's crucial because:

• It helps predict how much of each reactant you will need or have left over after a reaction.
• Stoichiometry uses the concept of the mole to accurately determine the amounts of reactants and products, as seen in our titration exercise where moles of KHP and NaOH were determined.

In summary, understanding stoichiometry can simplify what might initially seem like complex chemistry calculations, especially in acid-base reactions like titration.