am lost. I have to create a buffer using NH4CL and 0.10 M NH3. I have to chose how much of the reagent to use in order to get a concentration between 0.01 and .5 M. Then after I come up with the recipe for that I have to calculate the pH based on the concentrations using the Henderson-Hasselbalch equation. We have not gone over this in class so I'm on my own and lost. Can anyone help?? With NH4Cl being a solid I have to calculate how many grams of the solid to dissolve into 100 mL of the solution. I also know that the Ka value of NH4 is 5.6 x 10 to the -10power.
What's wrong with what I gave you last night? The directions are there; I made 1 L of solution so adjust to 100 mL for this and you have it. I'll be glad to help you through it but I don't want to do the work for you.
To create a buffer solution using NH4Cl and NH3, you need to consider the Henderson-Hasselbalch equation, which relates the ratio of the concentrations of the conjugate acid-base pair to the pH of the solution. The Henderson-Hasselbalch equation is given as:
pH = pKa + log ([A-]/[HA])
where pH is the desired pH of the buffer, pKa is the negative logarithm of the acid dissociation constant of the acid (in this case NH4+), [A-] is the concentration of the conjugate base (NH3), and [HA] is the concentration of the acid (NH4+).
To begin, you need to choose the desired pH of your buffer within the range of 0.01 to 0.5. Let's assume you want a pH of 0.1 for this example.
1. Calculate the concentration of NH3 ([A-]):
Since you want the concentration in the range of 0.01 to 0.5 M, you can choose any concentration within this range. For simplicity, let's choose a concentration of 0.10 M NH3.
2. Calculate the concentration of NH4+ ([HA]):
Using the equation: pH = pKa + log ([A-]/[HA]), we can rearrange it to find [HA]:
[HA] = [A-] / 10^(pH - pKa)
Here pKa is the negative logarithm of the Ka value of NH4+ (Ka = 5.6 x 10^-10), so pKa = -log(5.6 x 10^-10).
Substitute the values into the equation:
[HA] = 0.10 M / 10^(0.1 - (-log(5.6 x 10^-10)))
3. Calculate the moles of NH4Cl needed:
Now, you know the concentration of NH4+ ([HA]) and the volume of the solution (100 mL or 0.100 L). To find the moles of NH4Cl needed, you can use the equation: moles = concentration x volume.
moles = [HA] x volume
Convert the volume to liters: 0.100 L.
Substitute the values into the equation:
moles = [HA] x 0.100 L
4. Convert moles of NH4Cl to grams:
To calculate the mass of NH4Cl needed to dissolve in 100 mL of the solution, use the equation: mass = moles x molar mass.
First, find the molar mass of NH4Cl (NH4: 14.01 g/mol, Cl: 35.45 g/mol).
Substitute the values into the equation:
mass = moles x molar mass
Now, by following these steps, you can find the appropriate amount of NH4Cl to dissolve into 100 mL of the buffer solution. Once you have prepared the buffer, you can calculate the pH using the Henderson-Hasselbalch equation and the given concentrations of NH4+ and NH3.