Question

Suppose 0.01 moles of HCl are dissolved in 1 kg water. The solution is then allowed to reach

equilibrium. The temperature is 298.15K and the pressure is 1bar. HCl completely
dissociates in water by the reaction
HCl →H+ + Cl-
What is the pH of the solution? (calculate the concentration by molality)

Answer 1

To calculate the pH of the solution, we can use the concentration of hydrogen ions and the concept of molality. The concentration of HCl in the solution is 0.01 mol/kg of water. By calculating the concentration of H+ ions using molality and the number of water molecules, we can determine the pH of the solution.

Step-by-step explanation:

The pH of a solution can be calculated using the concentration of hydrogen ions. The concentration of hydrogen ions in pure water is 1 × 10-7 moles H+ ions per liter of water. To calculate the pH, we need to determine the concentration of H+ ions in the given solution.

The concentration of HCl in the solution can be calculated using molality. Molality is the amount of solute (in moles) divided by the mass of the solvent (in kg). In this case, we have 0.01 moles of HCl dissolved in 1 kg of water.

Molality (m) = moles of solute / mass of solvent

Using the given values, molality = 0.01 moles / 1 kg = 0.01 mol/kg

Now, we can calculate the concentration of H+ ions in the solution using the formula:

H3O+ concentration (mol/L) = molality * number of water molecules

Number of water molecules = 6.02 × 1023

Let's substitute the values and calculate the concentration:

H3O+ concentration = 0.01 mol/kg * 6.02 × 1023 mol

Using the negative logarithmic scale (pH = -log[H3O+]), the pH of the solution can be calculated.