A 20.0-mL sample of 0.125 M HNO3 is titrated with 0.150 M NaOH. Calculate the pH for at least five different points on the titration curve and sketch the curve. Indicate the volume at the equivalence point on your graph.

Understanding how to calculate pH is crucial in a wide range of chemistry applications, especially in acid-base titrations.
To begin with, pH is a scale used to measure the acidity or basicity of an aqueous solution. It is the negative logarithm of the hydrogen ion concentration, expressed mathematically as \( pH = -\log[H^+] \). The pH scale ranges from 0 to 14, with 7 being neutral, values below 7 indicating acidity, and values above 7 indicating basicity.
For a strong acid like nitric acid (HNO3), which dissociates completely in water, the initial pH can be calculated directly from its molarity. For example, with a 0.125 M HNO3 solution, the pH is \( -\log(0.125) \), which you can determine using a calculator.

• For pH calculation before the equivalence point, one must account for the remaining HNO3 after a certain volume of NaOH has been added.
• After the equivalence point, the pH depends on the excess OH- ions present from the titrant, NaOH, in this case.

These calculations require an understanding of mole relations and the stoichiometry of the titration reaction.

The equivalence point is a crucial concept in titrations as it signifies the moment when the amount of titrant added equals the amount of substance originally present in the solution.
During an acid-base titration, the equivalence point is reached when the number of moles of acid equals the number of moles of base, indicating that the acid has been completely neutralized.
Calculating the equivalence point is done using the reaction's stoichiometry: \( V_1 \times M_1 = V_2 \times M_2 \), where \( V_1 \) and \( M_1 \) are the volume and molarity of the acid, and \( V_2 \) and \( M_2 \) are the volume and molarity of the base.

• The stoichiometry of the reaction between HNO3 and NaOH is 1:1.
• Using the information provided and the formula, one can calculate the volume of NaOH needed to reach the equivalence point.

This precise point affects the shape of the titration curve and is significant in determining the concentration of an unknown solution.

A titration curve is a graphical representation that shows the change in pH of the analyte solution as a titrant is added. This curve is instrumental in visualizing the titration process and identifying the equivalence point.
In the case of our strong acid (HNO3) and strong base (NaOH) titration, the plot begins with a low pH value that increases as the base is added. The steepness of the curve changes as the reaction approaches the equivalence point, after which there's a sharp rise in pH.

• The initial portion of the curve represents the pH changes when small volumes of NaOH are added to the acidic solution.
• The middle steep region where rapid pH change occurs is where the equivalence point lies.
• The latter part of the curve indicates the pH after the equivalence point, reflecting the pH of the excess base.

To sketch the curve, one calculates the pH at various volumes of NaOH added and plots these pH values against the corresponding volumes. The equivalence point is marked where the quantity of HNO3 originally present in the solution has been neutralized by NaOH. Understanding titration curves is essential for interpreting the results of a titration experiment and for determining the end point of a titration.