Question

what is the ph of the resulting solution if 45 ml of 0.432 m methylamine, ch3nh2, is added to 15 ml of 0.234 m hcl? assume that the volumes of the solutions are additive. ka

Answer 1

To find the pH when methylamine is mixed with HCl, one must first determine the limiting reactant and measure the moles of each reactant. Then use the Henderson-Hasselbalch equation to calculate the pH, given the concentrations of the base and conjugate acid formed. The exact pH calculation requires the pKa value for methylamine, which is not provided.

Step-by-step explanation:

To calculate the pH of the resulting solution when 45 mL of 0.432 M methylamine (CH3NH2) is mixed with 15 mL of 0.234 M HCl, one must first determine the reaction that occurs between the base (methylamine) and the acid (HCl).

Methylamine is a weak base and HCl is a strong acid. When mixed, they will react to form methylammonium chloride (CH3NH3+ Cl-) and water.

The reaction proceeds to completion due to the strong acid.

Next, we need to determine the limiting reactant.

We do this by calculating the moles of each reactant:

Moles of CH3NH2 = 45 mL * 0.432 M = 0.01944 moles

Moles of HCl = 15 mL * 0.234 M = 0.00351 moles

Since the moles of HCl are less than the moles of CH3NH2, HCl is the limiting reactant, and all of it will react with the CH3NH2.

This will leave us with some unreacted CH3NH2.

The buffer solution formed will contain the weak base (CH3NH2) and its conjugate acid (CH3NH3+).

We will use the Henderson-Hasselbalch equation to find the pH:

pH = pKa + log([base]/[acid])

In a real scenario, we would look up the pKa value, and then calculate the pH using the formula above, given the known concentrations of the base and conjugate acid after the reaction.

Answer 2

The pH of the solution can be calculated by determining the moles of methylamine and HCl, then using the Henderson-Hasselbalch equation considering the reaction between the weak base and the strong acid.

Step-by-step explanation:

The student is asking about the pH of the resulting solution when a certain volume of methylamine solution is mixed with a specific amount of HCl solution. To solve this, the reaction between methylamine, a weak base, and HCl, a strong acid, must be considered, which forms the corresponding methylammonium chloride and water. The molar amounts of each reactant must be calculated, and the limiting reactant should be identified. Since the volume of methylamine and HCl solutions have different molarities, it's important to calculate the moles of each, which is done by multiplying the molarity by the volume.

Once the limiting reactant is determined, one can calculate the concentration of the resulting ions and use the Henderson-Hasselbalch equation to find the pH of the solution. In this scenario, the exact values necessary to perform this calculation are not given, so a generic approach to how to solve such problems is provided instead.