Previously in Chem104: the concept of K w the concept of the K w circle p-functions (pH, pK a, pK w ) pH scale P-functions in calcs Today in Chem104: How K a relates to K b and pK a to pK b More ways to use the K w circle Group worksheet on The Most Important Equilibrium on the Planet (Part 1) What I had to use to find logarithms

Lauren said: “Cl- is a very weak base because HCl is a strong acid” How did she know that? AH + H 2 OA - + H 3 O+ acid conjugate base conjugate acid Now write the K a expression for AH and the K b expression for A-.

K w = Alright, now we’re can understand what Lauren said: We proved K w = K a x K b Use the K w circle! KaKa KbKb

KwKw If AH has a larger K a, like then A- must have a smaller K b like KaKa KbKb The stronger the acid (K a large), the weaker the conjugate base, (K b small) Because K w = K a x K b must =

KwKw KaKa KbKb If A- has a larger K b, like then AH must have a smaller K a like The stronger the base (K b large), the weaker the conjugate acid, (K a small) Because K w = K a x K b must =

Now do the same with K w = K a x K b = p of K w = p of [K a x K b ] = p of Let’s apply P-Functions We already did this one: K w = [H 3 O+][OH-] =  pK w = pH + pOH = 14 -log K w = -log (K a x K b )= -log pK w = pK a + pK b = 14 -log K w = -log K a + ( -log K b ) = -log

pK w Now apply this equation: pK w = pK a + pK b = 14 to this picture pK a pK b

Let’s do some problems !!