Preferência por Buffer de Formiato

Prévia do material em texto

Special Topic I 57 [A⁻] = 0.26 M [HA] = 0.74 M The solution must have [formic acid] = 0.74 M and [sodium formate] = 0.26 M. 12. At pH = 4.20, 74% of the formate buffer will be in the basic form. pH = 4.20, = 6.31 X Formic acid has a = 3.75, = 1.78 X K 1.78 X 10⁻⁴ + = = 1.78 X 10⁻⁴ + 6.31 X 10⁻⁵ 1.78 X 10⁻⁴ + 0.63 X 10⁻⁴ = 2.41 X 10⁻⁴ = 0.74 At pH = 4.20, 22% of the acetate buffer will be in the basic form. pH = 4.20, = 6.31 X Acetic acid has a pKa = 4.76, = 1.74 X 10⁻⁵. Kₐ 1.74x10⁻⁵ = 1.74 X 10⁻⁵ + 6.31 X 10⁻⁵ 1.78 X 10⁻⁵ = 8.05 X 10⁻⁵ = 0.22 The reaction to be carried out will generate protons that will react with the basic form of the buffer in order to keep the pH constant. Therefore, the formate buffer is preferred because it has a greater percentage of the buffer in the basic form.