Consider ammonia, what is the pH of a buffer solution prepared by adding 15.0 g of ammonium chloride to 5.00L of 0.200 M ammonia? ( the K for NH3 is given to me 1.80 x 10 to the power of -5)
Use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)]
pKa for NH3 is Kw/Kb. You were given Kb.
The base is NH3. The acid is NH4Cl (the NH4^+ in NH4Cl).
Post your work if you get stuck.
what is the Kw?
Ion product for H2O. Mathematically it is
(H^+)(OH^-) = Kw = 1 x 10^-14 and pKw = 14
The problem doesn't gave a Ka for NH3 but it gives a Kb; therefore, KaKb = Kw and Ka = Kw/Kb = 1 x 10^-14/1.80 x 10^-5 = ??
i found the pH to be 9.75, i don't know if i did it right,
Assuming i did it right, there is another question stating what is the pH of the buffer after 90.0mL of 2.00M HCL are added?...
I worked it and obtained 9.80 but I could have goofed. Here is what I did; you need to confirm it.
kb = 1.80 x 10^-5. pKb = 4.74 and that subtracted from pKw of 14 = 9.26
pH = 9.26 + (1.00/0.28)
pH = 9.26 + 3.57 = 9.26+0.55 = 9.81.
(NH4Cl) = 15/53.49 = 0.280 and in 1 L makes it 0.280 M.
For the next part, calculate the number of moles added with 90.0 mL of 2.00 M HCl. Buffers work (basic ones), when acids such as HCl are added, by neutralizing the strong acid with the NH3. The reaction HCl + NH3 ==>NH4Cl + H2O decreases the NH3 concn and increases the NH4^+ concn by the number of moles HCl added. Just recalculate the new concns of base and acid, plug into the H-H equation. and redetermine the pH. If you want it checked, please repost (with problem) at the top of the board and someone will look at it.
Can I just response to you without an account?
To find the pH of the buffer solution, we need to determine the concentration of ammonium ions (NH4+) and ammonia (NH3) in the solution.
First, let's calculate the concentration of ammonium ions (NH4+). We have 15.0 g of ammonium chloride (NH4Cl) and we need to convert it to moles:
Mass of NH4Cl = 15.0 g
Molar mass of NH4Cl = 53.5 g/mol (1 nitrogen atom + 4 hydrogen atoms + 1 chlorine atom)
Number of moles of NH4Cl = Mass / Molar mass = 15.0 g / 53.5 g/mol
Next, we need to determine the moles of ammonium ions (NH4+). Since ammonium chloride dissociates into one NH4+ ion and one Cl- ion, the number of moles of NH4+ is equal to the moles of NH4Cl:
Number of moles of NH4+ = Number of moles of NH4Cl
Now, let's calculate the concentration of NH4+ in the solution. We know that we have 5.00 L of 0.200 M ammonia. Since ammonia is a weak base and will form NH4+ in the presence of water, we can say that the concentration of NH4+ is equal to the moles of NH4+ divided by the total volume of the solution:
Concentration of NH4+ = Moles of NH4+ / Volume of solution
Now, let's find the moles of NH3 (ammonia) in the solution. We have 5.00 L of 0.200 M ammonia, so the moles of NH3 can be calculated as follows:
Moles of NH3 = Concentration of NH3 x Volume of solution
Since NH3 is a weak base and will partially dissociate into NH4+ and OH- ions, we need to find the OH- concentration in the solution. Using the given value of the dissociation constant (Kb) of NH3 (1.80 x 10^-5), we can calculate the OH- concentration:
OH- concentration = √(Kb x Concentration of NH3)
Finally, we can calculate the pOH (the negative logarithm of the OH- concentration) and then find the pH using the equation: pH = 14 - pOH.
Substituting the values into the equation, we can find the pH of the buffer solution.