GChem Question

[BaylorDDS]

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Can someone walk me through this question:
"How many moles of NH4Cl must be added to 2L of .1M NH3 to form a buffer whose pH is 9? (assume the addition of NH4Cl doesn't change the volume of solution) Kb=1.8e-5.

*Without henderson-hasselbach por favor.

 

[pbure9]

I'm not a 100%, but for kb youd have to write out the equation as:
NH3 + H20 --> NH4+ + OH-

then if pH is 9, pOH is 5, therefore concentration of OH- is 1E-5.
kb = [NH4+][OH-]/[NH3]
[(x/2)(1E-5)]/(.1) ... it's over 2 since you want Molarity (moles/volume)

so you're left with 1E-5(x/2)/.1 = the kb = 1.8E-5
that becomes 1E-4x/2=kb ==> or 5E-5x=kb
so then you get, x = .36 moles NH4Cl

lemme know how this looks 😉