How many grams of dry NH4Cl need to be added to 1.80L of 0.200M solution of ammonia,NH3, to prepare a buffer that has a pH of 8.69? Kb for ammonia is 1.8*10^-5
Use the Henderson-Hasselbalch equation.
pH = pKa + log[(base)/(acid)]
You know pKa for NH3 (you have Kb listed but pKa = 14-pKb), you know pH, and you know (base). Calculate (acid), which is the NH4Cl, and go from concn to moles to grams. Post your work if get stuck.
thankyou it helped
im a ninja
Can u do the steps please with the numbers
To calculate the number of grams of NH4Cl needed to prepare the buffer solution, we can follow these steps:
Step 1: Write the balanced chemical equation for the reaction between NH3 (ammonia) and NH4Cl (ammonium chloride):
NH3 + H2O ⇌ NH4+ + OH-
Step 2: Identify the equilibrium expression for the reaction:
Kb = [NH4+][OH-] / [NH3]
Step 3: Calculate the concentration of OH- ions needed to achieve a pH of 8.69 using the equation:
pOH = 14 - pH
pOH = 14 - 8.69 = 5.31
Step 4: Calculate the concentration of OH- ions using the equation:
OH- concentration = 10^(-pOH)
Step 5: Use the OH- concentration to calculate the concentration of NH4+ ions at equilibrium using the equation:
[NH4+] = [OH-]
Step 6: Calculate the concentration of NH3 using the equation:
[NH3] = initial concentration of NH3 - [NH4+]
Step 7: Write the expression for Kb and substitute the known values:
1.8 × 10^-5 = [NH4+] × [OH-] / [NH3]
Step 8: Substitute the calculated concentration values in the Kb expression:
1.8 × 10^-5 = [OH-] × [OH-] / ([NH3] - [OH-])
Step 9: Rearrange the equation and express [OH-] in terms of [NH3]:
[OH-] = √ (1.8 × 10^-5 × ([NH3] - [OH-]))
Step 10: Solve the equation for [OH-]. Let's assume [NH3] - [OH-] ≈ [NH3]. Square both sides of the equation:
[OH-]^2 = 1.8 × 10^-5 × [NH3]
Step 11: Solve for [OH-]:
[OH-] ≈ √ (1.8 × 10^-5 × [NH3])
Step 12: Substitute [NH3] - [OH-] ≈ [NH3] in the equilibrium expression (step 5):
[NH4+] = √ (1.8 × 10^-5 × [NH3])
Step 13: Now, we can convert the concentration of NH4+ ([NH4+]) to moles of NH4+, using the given volume of the solution. The equation to use is:
moles = concentration × volume
Step 14: Convert moles of NH4+ to grams of NH4+, using the molar mass of NH4Cl (53.49 g/mol).
By following these steps, you should be able to calculate the grams of NH4Cl required to prepare the buffer solution with a pH of 8.69.