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Modify Equation 6.6 for bases. % = Kbco×100% = 1.8×10-50.12×100% = 1.2% (less than 5% so assumption valid) 75. What are the concentrations of all P containing species in 0.084 M K3PO4? What is the pH of the solution? 1) PO43-+ H2O UHPO42-+ OH1-K = Kw/Ka=1.0x10-14/4.8x10-13= 0.021; Let x = [HPO42-]=[OH1-] & 0.084-x = [PO43-] x20.084-x= 0.021; x2+ 0.021 x - 1.75×10-3= 0x = −0.021 + (0.021)2-4(1)(-1.75×10-3)2(1)= 0.033 M = [OH1-] = [HPO41-][PO43-] = 0.084 - 0.033 = 0.051 M2) HPO42-+ H2O UH2PO41-+ OH1-K2= Kw/Ka=1.0x10-14/6.2x10-8= 1.6x10-7Small K, so assume x is negligible, which means that [H2PO41-] = K2= 1.6x10-7M 3) H2PO42-+ H2O UH3PO4+ OH1-K3=1.0x10-14/7.5x10-3= 1.3x10-12; [OH1-] = 0.033 M & [H2PO41-] = 1.6x10-7M 1.3×10-12= [H3PO4](0.033)1.6×10-7;[H3PO4] = (1.3×10-12)(1.6×10-7)0.033= 6.5×10-18M pOH = -log(0.033) = 1.48; pH = 14.00 – 1.48 = 12.52 77. Define the term salt. Given an example of a neutral, a basic, and an acidic salt. A salt is an ionic compound formed in an acid-base reaction. Neutral: KClO4; Basic: KCN; Acidic: NH4NO3. 79. Indicate whether each of the following is an acidic, a basic, or a neutral salt. a) K2SO4neutralb) K2SO3basicc) KHSO4acidicd) K2CO3basice) KOCl basicf) NH4OCl basic (Kb> Ka)81. What is the pH of each of the following salt solutions? a) 0.12 M NH4Cl NH41+is acidic, while Cl1-is neutral, so NH4Cl is an acidic salt: 1+10-63[H O] = (5.610)(0.12) = 8.210M; pH = 5.09××b)0.096 M KCN K1+is neutral, but CN1-is basic, so KCN is a basic salt: -14-5b-101.010K= = 2.5104.010×××1--5-3[OH] = (2.510)(0.096) = 1.5510M; pOH = 2.81; pH = 11.19××c)0.10 M KHSO3 K1+is neutral, and HSO31-is amphiprotic, so use Equation 6.12. pH = ½(pK1+ pK2) = ½(1.82 + 7.00) = 4.41
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