An acetic acid/ sodium acetate buffer solution similar to the one you made in the lab was prepared using the following components: 3.46 g of NaC2H3O2∙3H2O (FW. 136 g/mol) 9.0 mL of 3.0 M HC2H3O2 55.0 mL of water If you take half of this solution and add 2 mL of 1.00 M NaOH to it, then what is the pH of this new solution?
this is a buffer since
HC2H3O2 = weak acid
NaC2H3O2 = conjugate base
are present
so we must model this as a buffer, use henderson hasselbach equations
pH = pKa + log(base/acid)
pH = pKa + log(NaC2H3O2 /HC2H3O2 )
pKa = 4.75 for HC2H3O2
initially
mol of NaC2H3O2 = mass/MW = 3.46/136 = 0.0254
mol of HC2H3O2 = MV = 9*3*10^-3 = 0.027
after adding
mol ofNaOH = MV = 2*1 = 2*10^-3 mol
mol of NaC2H3O2 = 0.0254 - 2*10^-3 = 0.0234
mol of HC2H3O2 = 0.027+ 2*10^-3 = 0.029
now..
pH = pKa + log(NaC2H3O2 /HC2H3O2 )
pH = 4.75+ log(0.0234/0.029)
pH = 4.6568
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