A 40.0 mL sample of a mixture of HCl and H₃PO₄ was titrated with 0.100 M NaOH. The first equivalence point was reached after 88.0 mL of base, and the second equivalence point was reached after 126.4 mL of base. (c) What percent of the HCl is neutralized at the first equivalence point?

Verified step by step guidance

1. First, understand that the first equivalence point in a titration is when all of the acid in the solution has been neutralized by the base. In this case, the first equivalence point was reached after 88.0 mL of NaOH was added, meaning all of the HCl was neutralized.
2. Next, calculate the moles of NaOH used to reach the first equivalence point. This can be done using the formula: moles = Molarity * Volume. The molarity of NaOH is given as 0.100 M and the volume used to reach the first equivalence point is 88.0 mL (or 0.088 L).
3. Since HCl and NaOH react in a 1:1 ratio, the moles of NaOH used to reach the first equivalence point is equal to the moles of HCl in the original solution.
4. Then, calculate the molarity of HCl in the original solution using the formula: Molarity = moles / Volume. The volume of the original solution is given as 40.0 mL (or 0.040 L).
5. Finally, to find the percent of HCl neutralized at the first equivalence point, understand that 100% of the HCl is neutralized at this point. This is because the definition of the equivalence point is when all of the acid (in this case, HCl) has been neutralized by the base (NaOH).

Key Concepts

Titration and Equivalence Points

Titration is a quantitative analytical method used to determine the concentration of a solute in a solution. The equivalence point in a titration is reached when the amount of titrant added is stoichiometrically equivalent to the amount of substance in the sample. In this case, the first equivalence point indicates the complete neutralization of HCl, while the second equivalence point involves the neutralization of H3PO4.

Stoichiometry of Acid-Base Reactions

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. For the titration of HCl with NaOH, the reaction is a 1:1 ratio, meaning one mole of HCl reacts with one mole of NaOH. Understanding this ratio is crucial for determining how much HCl is neutralized at the first equivalence point.

Concentration and Volume Relationships

The relationship between concentration and volume is essential in titration calculations. The formula C1V1 = C2V2 relates the concentrations and volumes of the acid and base involved. By knowing the concentration of NaOH and the volume used to reach the first equivalence point, one can calculate the moles of HCl neutralized and subsequently determine the percentage of HCl in the original mixture.