a) water pH before mixing = pH after mixing= pH change = Solution 10.0 mL 3.22 M
ID: 607625 • Letter: A
Question
a) water
pH before mixing = pH after mixing= pH change =Explanation / Answer
10.0 mL 3.22 M HCl + 420 mL water pH before mixing= -0.51 for HCl and 7 for water pH after mixing= 1.13 pH change= 1.64 b) 10.0 mL 3.22 M HCl + 420 mL 0.160 M CH3COO- reaction: HCl + CH3COO- --> CH3COOH + Cl- we have 32.22 mmoles of HCl and 67.20 mmoles of CH3COO-, so we will obtain 67.20-32.22=34.98 mmoles of CH3COO and 32.22 mmoles of CH3COOH in a total of 430 mL. This is a buffer solution. pH before mixing=-0.51 for HCl and x2/0.160=1.8E-5 and pOH=2.77 and pH=11.23 for CH3COO- pH after mixing= pH=pKa-log[Cb/Ca]=4.74-log[(34.98/430)/(… pH change=-6.52 c) we already have 10 mL 32.22 mmoles of HCl and we add 420 mL 0.160 M CH3COOH in this case. pH before mixing= -0.51 for HCl and x2/0.160=1.8E-5 and pH=2.77 for CH3COOH pH after mixing= we have a strong acid accompanied by a weak acid We will sum the H(+) ions then: H(+) ions from HCl=32.22 mmoles H(+) ions from CH3COOH= x2/0.160=1.8E-5, x=0.0017 M 420 mL=0.712 mmoles total=32.932 mmoles total volume=430 milliliters concentration= 0.0766 M, pH=1.12 pH change= 1.12-2.77=-1.65 d) pH before mixing= -0.51 for HCl and what about the pH of buffer solution? pH=pKa-log(Cb/Ca)=4.74-log(1)=4.74 for the buffer solution. pH after mixing=? the basic component in the buffer solution will react with HCl first: HCl + CH3COO- --> CH3COOH + H2O We have 32.22 mmoles of HCl and 67.2 mmoles of CH3COO (and CH3COOH, but we will not use the latter now). So, we will react these two to obtain 32.22 mmoles of CH3COOH and we will have 34.98 mmoles of CH3COO remaining. We had 67.2 mmoles of CH3COOH before, so the total amount of CH3COOH will be 67.2+34.98=102.18 mmoles in 430 mL of a solution, so the concentration will be 0.238 M of CH3COOH. 1.8E-5=x2/0.238 and x (H+ ion concentration)=0.002 M, so the pH=2.68 pH change= 2.68-4.74=-2.06
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