College X wwww.saplinglearning.com/ibiscms/mod/ibis/view.php?id-3016485 Print Ca

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College X wwww.saplinglearning.com/ibiscms/mod/ibis/view.php?id-3016485 Print Calculator Periodic Table Question 8 of 6 What concentrations of acetic acid and acetate would be requir to a 0.20 M buffer solution at pH 4.9? Note that the concentration and/or pH value may differ from that in the first question STRATEGY solve for the ratio of base (acetate) to acid (acetic 1. Rearrange the Henderson-Hasselbalch equation to CA 2. Use the mole fraction of acetate to calculate the concentration of acetate. 3. Calculate the concentration of acetic acid. That is, there are 1.4 molecules Step 1: The ratio of base to acid is 1.4 of acetate for each molecule of acetic acid. Step 2. The mole fraction of acetate is 0.58, and the concentration of acetate is 0.12. Step 3: Calculate the concentration of acetic acid. Number acetic acid Previous B Give up & View solution Check Answer Navi Extr s Hunt

Explanation / Answer

Apply buffer equation

p H= pKa + log(A-/HA)

then

4.9 = 4.76 + log(A-/HA)

solve for ratio

A-/HA = 10^(4.9-4.76) = 1.38

[A-] = 1.38*[HA]

and

[A-] + [HA] = 0.2

substitute

1.38*[HA] + [HA] = 0.2

[HA] = 0.2/(1.38 +1) = 0.084 M

[A-] = 1.38*0.084 = 0.1159 M

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