08_Lecture0

# 267 very low acid or base concentrations now check

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Unformatted text preview: H9H+][OH–]/[CN3H9N:] 0.00185 6.35 × 10 = [X][X]/[0.0557–X]; X = ___ = [OH–] Then get pOH to get pH (ignore OH– from H2O?) –5 11.267 Very Low Acid or Base Concentrations • Now check the autoprotolysis of water…also a source of H+ and OH–. • [H+] = [H+]acid + [H+]water • [H+] = Cacid + [H+]water • [H+] = Cacid + [OH–]water [OH • [H+] = Cacid + Kw/[H+] ……algebra happens • 0 = [H+]2 – Cacid [H+] – Kw [H 8 • What would be the pH of a 1.0 x 10--8 M HCl soln? HCl • (1) Without considering H+ from water: pH = 8.00 (Is this realistic?) • (2) With considering H+ from water: pH = 6.96 pH Mixing Weak Acids with Their Conjugate Bases OneWhat would be the –resulting pH source for HA and A is from the acid itself. 1.5 that anothercetic acid (Ka = be if To × 10–3 M a source for A– will added. Ka× 10–5) is mixedadjustment. 1.75 may need some with 0.50 [HA]-3= C cetateH+] • Mass balance for HA: × 10 M aHA – [ ion? 0 = [H+]2 + 5.18 x 10–4[H+] – 2.625 x 10–8 Mass balance for A–: [A–] = C + [H+] A– 4.65 ×10–6; pH = 4.33 Did We Just Make a Buffer? Did • Buffers are solutions that RESIST pH changes. Buffers RESIST • They are made from a weak acid + its They conjugate or weak base + its conjugate. (Cannot conjugate do this with...
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