Two 1.2-kip forces are applied to an L-shaped machine element Review AB as shown. Determine the normal and shearing stresses at(a) point a, (b) point b, (c) point c.
Calculations with Ka & Kb Values • for a conjugate acid-base pair, Ka x Kb = Kw, where Kw = 1.0 x 10^-14 at 25˚C ex. Is a solution of NH4HC2O4 at 25˚C acidic, basic, or neutral • Ka C2H2O4 = 5.6 x 10^-2 Kb NH3 = 1.8 x 10^-5 Solve for new Ka for NH4+ + H2O⁶NH3 + H3O+ Ka* = 1.0 x 10^-14 = 5.56 x 10^-10 *Use Ka* = Kw 1.8 x 10^-5 Kb Solve for new Kb for C2H2O4 + H2O⁶HC2H2O4+ + OH- Kb* = 1.0 x 10^-14 = 1.79 x 10^-13 *Use Kb* = Kw 5.6 x 10^-2 Ka Choose bigger K value 5.56 x 10^-10 > 1.79 x 10^-13 Since Ka* > Kb*, NH4HC2O4 is acidic (at 25˚C). • ex. Calculate pH of a 0.10 M NH4NO3 solution. Kb NH3 = 1.8 x 10^-5 NH4+(aq) + H2O(l) ⁶ NH3(aq) + H3O+(aq) I 0.10 M 0 M 0 M C -x +x +x E 0.10 - x x x Ka* = 1 x 10^-14 = 5.56 x 10^-10 1.8 x 10^-5 5.56 x 10^-10 = x^2 0.1 - x Neglect x 5.56 x 10^-10 (0.1) = x^2 x = 7.46 x 10^-6 7.46 x 10^-6 x 100 = 0.0075% < 5% ✓ 0.10 pH = -log[H3O+] = -log(7.46 x 10^-6) = 5.13
