What is the ph of a .05 L solution containing .075 mol NH3 and 6.80 g of NH4+ when .025 L of 2 M is added to it? Kb= 1.8 x10^-5
When 0.025 L of 2M WHAT is added to it.
Use the Henderson-Hasselbalch equation and set up an ICE chart with it. If you will show your work I can help you through it.
Do i use Ka or Kb?
The HH equation uses pKa. Don't have pKa? Remember to convert Kb to pKb, then
pKa + pKb = pKw = 14
To find the pH of the solution, we need to calculate the concentration of the OH- ions first.
Given:
- Volume of the solution = 0.05 L
- Moles of NH3 = 0.075 mol
- Mass of NH4+ = 6.80 g
- Volume of the 2 M HCl solution added = 0.025 L
- Kb value for NH3 = 1.8 x 10^-5
Step 1: Calculate the concentration of NH3
Given the moles of NH3 (0.075 mol) and the volume of the solution (0.05 L), the concentration can be calculated using the formula:
Concentration of NH3 (M) = Moles of NH3 / Volume of solution (L)
Concentration of NH3 = 0.075 mol / 0.05 L = 1.5 M
Step 2: Calculate the concentration of OH- ions
Since NH3 is a weak base, it reacts with water to form OH- ions. Using the Kb value, we can calculate the concentration of OH- ions.
Kb = [NH4+] [OH-] / [NH3]
1.8 x 10^-5 = (x)(x) / (1.5 - x)
Since the concentration of OH- is equivalent to the concentration of NH4+ (assuming complete ionization of NH4+), we can assume x moles of OH- and NH4+ are formed.
1.8 x 10^-5 = x^2 / (1.5 - x)
Solving this quadratic equation will help us find x, which represents the concentration of OH- ions.
Step 3: Calculate the concentration of NH4+
Given the mass of NH4+ (6.80 g), we need to convert it to moles to calculate the concentration.
The molar mass of NH4+ = 18.03 g/mol
Moles of NH4+ = Mass of NH4+ / Molar mass of NH4+
Moles of NH4+ = 6.80 g / 18.03 g/mol
Step 4: Adding HCl
HCl is a strong acid that completely dissociates in water. Since 0.025 L of 2 M HCl was added, we can calculate the moles of H+ ions that were added to the solution.
Moles of HCl = Concentration of HCl (M) * Volume of HCl solution (L)
Moles of HCl = 2 M * 0.025 L
Step 5: Calculate the final concentration of NH4+ and OH- ions
The addition of H+ ions from HCl reacts with NH3 and NH4+ ions, forming NH4+ ions. Based on the mole ratio, we can determine the final concentration of NH4+.
Moles of NH4+ = Initial moles of NH4+ + Moles of HCl
Final concentration of NH4+ = Moles of NH4+ / Volume of solution (L)
Additionally, the OH- concentration formed by the reaction between HCl and NH3 can be calculated by using the stoichiometry.
OH- concentration = Initial concentration of OH- + H+ ions / Volume of solution (L)
Step 6: Calculate the pOH and pH of the solution
Since pOH = -log10(OH- concentration) and pH + pOH = 14, we can calculate pH using the concentration of OH- ions.
pOH = -log10(OH- concentration)
pH = 14 - pOH
Following these steps will allow you to calculate the pH of the solution. Simply substitute the known values into the equations and solve for the unknowns accordingly.