Will this solution form a buffer?

100 mL of .10 M NH3; 100 mL of .15 M NH4Cl

Work:
NH3= .01 moles
NH4Cl= .015 moles
.... not sure what else to do.

I think we use the H-H equation, but I don't know how to find pKa, or even what pKa is. This should give the pH of the solution, but I don't think the pH would indicate whether or not this solution would be a buffer? How do you know if a solution is a buffer, and how do you know if the solution is not a buffer?

Yes, use the H-H equation.

Find Ka = Kw/Kb. You know Kw for water and Kb for NH3. From Ka, find pKa.
NH3 =s the base
NH4Cl is the acid. Plug into HH and solve for pH. And, yes, it's a buffer. However, do you need to solve for pH. The question is, will it form a buffer. The answer is yes. It is a solution of a weak base and its salt. A weak acid and its salt also will form a buffer.

To determine whether this solution will form a buffer, you need to assess the criteria for a buffer solution. Here's how you can approach it step by step:

1. Calculate the moles of NH3 and NH4Cl present in the solution:

NH3: 100 mL x 0.10 M = 0.01 moles
NH4Cl: 100 mL x 0.15 M = 0.015 moles

You've already correctly calculated these values.

2. A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). In this case, NH3 is a weak base, and NH4Cl is its conjugate acid.

3. To determine if a solution is a buffer, you need both the weak acid/base pair and their ratio. The Henderson-Hasselbalch equation is commonly used to relate the pH of a buffer to the pKa of its acid. However, in this case, we don't need the pH or pKa as we can analyze the concentrations of NH3 and NH4Cl to determine if they are in the appropriate ratio for a buffer.

4. The general criteria for a buffer solution are:

a. The concentrations of the weak acid (NH4Cl) and its conjugate base (NH3) should be relatively similar in magnitude.
b. The ratio of [conjugate base]/[weak acid] (in this case, [NH3]/[NH4Cl]) should be within a certain range.

5. Typically, for an effective buffer solution, the ideal ratio is close to 1:1, where [NH3]/[NH4Cl] is approximately equal to 1. This equal concentration helps to maintain the pH of the solution when small amounts of acid or base are added.

6. In your case, the ratio of moles is 0.01/0.015, which simplifies to approximately 0.67 or 2:3. This ratio is not close to 1:1, so the solution does not meet the criteria for an ideal buffer solution.

Therefore, based on the given concentrations, the solution of 100 mL of 0.10 M NH3 and 100 mL of 0.15 M NH4Cl does not form an effective buffer.