DadospKa\mathsf{p}K_\mathsf{a}pKb\mathsf{p}K_\mathsf{b}
HF\ce{HF}3,4\pu{3,4}Anilina9,4\pu{9,4}
HClO\ce{HClO}7,5\pu{7,5}Trimetilamina4,2\pu{4,2}
HIOX3\ce{HIO3}0,8\pu{0,8}Piridina8,8\pu{8,8}
HClOX2\ce{HClO2}2,0\pu{2,0}Hidrazina5,8\pu{5,8}

Considere os pares de ácidos.

  1. HF\ce{HF} e HClO\ce{HClO}

  2. HIOX3\ce{HIO3} e HClOX2\ce{HClO2}

  3. CX6HX5NHX3X+\ce{C6H5NH3^+} e (CHX3)X3NHX+\ce{(CH3)3NH^+}

  4. CX5HX5NHX+\ce{C5H5NH^+} e NHX2NHX3X+\ce{NH2NH3^+}

Assinale a alternativa que relaciona os pares em que o primeiro ácido é mais forte.

Gabarito
  1. HF\ce{HF} : Ka=4⋅10−4K_a=\pu{4e-4} HClO\ce{HClO} : Ka=3⋅10−8K_a=\pu{3e-8} KaK_a (HF\ce{HF}) > KaK_a (HClO\ce{HClO})

  2. HIOX3\ce{HIO3} : Ka=1,7⋅10−1K_a=\pu{1,7e-1} HClOX2\ce{HClO2} : Ka=1e−2K_a=1e-2 KaK_a (HIOX3\ce{HIO3}) > KaK_a (HClOX2\ce{HClO2})

  3. CX6HX5NHX3X+\ce{C6H5NH3^+} : pKa=14−pKb  ⟹  pKa=4,6  ⟹  Ka=2,5⋅10−5pK_a=14-pK_b\implies pK_a=4,6\implies K_a=\pu{2,5e-5} (CHX3)X3NHX+\ce{(CH3)3NH^+} : pKa=14−pKb  ⟹  pKa=9,8  ⟹  Ka=1,6⋅10−10pK_a=14-pK_b\implies pK_a=9,8\implies K_a=\pu{1,6e-10} KaK_a (CX6HX5NHX3X+\ce{C6H5NH3^+}) > KaK_a ((CHX3)X3NHX+\ce{(CH3)3NH^+})

  4. CX5HX5NHX+\ce{C5H5NH^+} : pKa=14−pKb  ⟹  pKa=5,2  ⟹  Ka=6,3⋅10−6pK_a=14-pK_b\implies pK_a=5,2\implies K_a=\pu{6,3e-6} NHX2NHX3X+\ce{NH2NH3^+} : pKa=14−pKb  ⟹  pKa=8,2  ⟹  Ka=6,3⋅10−9pK_a=14-pK_b\implies pK_a=8,2\implies K_a=\pu{6,3e-9} KaK_a (CX5HX5NHX+\ce{C5H5NH^+}) > KaK_a (NHX2NHX3X+\ce{NH2NH3^+})