1) Three groups of students collected data for three different buffer systems. A
ID: 810726 • Letter: 1
Question
1) Three groups of students collected data for three different buffer systems. All of the groups forgot to write which buffer system they were using in their notebook. a) Assuming that the students used proper laboratory skills, use the literature values provided below for each possible buffer system to determine which plot of pH vs. log [base]/[acid] corresponds with which buffer system. Ka (ammonium) = 5.5 X 10^-10, Ka (acetic acid) =1.8 x 10^-5, and Ka (tris)=7.9 x 10^-9. (You must show work to receive credit.) b) For each of the three buffers, list the two main components that make up each buffer. (You may use abbreviations for the chemical names involved in the acetic acid buffer and the tris buffer.)Explanation / Answer
FIRST GRAPH
For acidic buffer
pH = pKa + log([X-] / [HX])
also acidic buffer has pH less than 7
acidic buffer is formed by salt of weak acid and only acetic acid is an acid amon these 3
hence first graph is a buffer of acetic acid , we can also check
pKa = -log(1.8*10^-5) = 4.74
when log([X-] / [HX])= -1
pH = 4.74 - 1 = 3.74 which satisfies the graph as well
SECOND GRAPH
its a basic buffer pH = pKa + log([X-] / [HX])
put log([X-] / [HX]) = -1
pKa = -log(5.5*10^-10) = 9.25
pH = 9.25 - 1 = 8.25
which satisfies the second graph
hence the third graph is for tris
Buffers -
Acetic acid - CH3COOH + CH3COONa (any other metal instead of Na is OK)
Ammonium - NH4OH + NH4Cl (any other anion instead of Cl is OK)
Tris - C4H11NO3 + C4H10NO2 Cl (any other anion instead of Cl is OK)
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