What mass of HI must be present in 0.250 L of solution to obtain a solution with each pH value?
a. pH = 1.25 b. pH = 1.75 c. pH = 2.85

Verified step by step guidance

1. Determine the concentration of hydrogen ions [H^+] in the solution using the pH value. Use the formula: [H^+] = 10^{-pH}.
2. Substitute the given pH value (1.75) into the formula to find [H^+].
3. Recognize that HI is a strong acid and dissociates completely in water, so the concentration of HI is equal to the concentration of [H^+].
4. Calculate the moles of HI required using the concentration of HI and the volume of the solution (0.250 L). Use the formula: moles of HI = [HI] * volume.
5. Convert the moles of HI to mass using the molar mass of HI. Use the formula: mass = moles * molar mass of HI.

Key Concepts

pH and Hydrogen Ion Concentration

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. A lower pH indicates a higher concentration of hydrogen ions (H+), while a higher pH indicates a lower concentration. For example, a pH of 1.75 corresponds to a hydrogen ion concentration of approximately 0.0178 M.

Molarity and Solution Concentration

Molarity (M) is a way to express the concentration of a solution, defined as the number of moles of solute per liter of solution. To find the mass of a solute needed to achieve a specific molarity, one can use the formula: mass = molarity × volume × molar mass. This concept is essential for calculating how much HI is required to reach the desired pH.

Dissociation of HI in Solution

Hydrogen iodide (HI) is a strong acid that completely dissociates in water to produce hydrogen ions (H+) and iodide ions (I-). This complete dissociation means that the concentration of H+ ions in the solution is equal to the concentration of HI initially added. Understanding this dissociation is crucial for determining the amount of HI needed to achieve a specific pH.