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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Chimystlearner on October 08, 2018, 01:02:24 PM

Title: Find pKa1,pKa2,pKa3 and the equivalence points of H3PO4
Post by: Chimystlearner on October 08, 2018, 01:02:24 PM

According to this table: (Note that it is a triprotic acid) So there will be 3 different pKa and 2 equivalence points.
H3PO4   NaOH   pH   Volumen total
0,1                     1,61   0,1
0,1   0,001          1,67   0,101
0,1   0,002          1,76   0,102
0,1   0,003          1,85   0,103
0,1   0,004          1,97   0,104
0,1   0,005          2,04   0,105
0,1   0,006          2,08   0,106
0,1   0,007          2,37   0,107
0,1   0,008          2,58   0,108
0,1   0,009          2,88   0,109
0,1   0,01                  3,68   0,11
0,1   0,011          5,5   0,111
0,1   0,012          6,06   0,112
0,1   0,013          6,29   0,113
0,1   0,014          6,5   0,114
0,1   0,015          6,67   0,115
0,1   0,016          6,84   0,116
0,1   0,017          7,01   0,117
0,1   0,018          7,27   0,118
0,1   0,019          7,56   0,119
0,1   0,02                  7,7   0,12
0,1   0,021         10,24   0,121
0,1   0,022         10,73   0,122
0,1   0,023         10,99   0,123
0,1   0,024         11,17   0,124
0,1   0,025         11,31   0,125
0,1   0,026         11,41   0,126
0,1   0,027         11,54   0,127
0,1   0,028         11,65   0,128
0,1   0,029         11,72   0,129
0,1   0,03                 11,82   0,13
0,1   0,031         11,88   0,131
0,1   0,032         11,95   0,132
0,1   0,033         12,02   0,133
0,1   0,034         12,08   0,134
0,1   0,035         12,12   0,135
0,1   0,036         12,13   0,136
0,1   0,037         12,18   0,137
0,1   0,038         12,21   0,138
0,1   0,039         12,24   0,139

Title: Re: Find pKa1,pKa2,pKa3 and the equivalence points of H3PO4
Post by: Babcock_Hall on October 08, 2018, 01:10:21 PM

According to the Forum Roles (see red link above) you must show your attempt first before we can help you.

Title: Re: Find pKa1,pKa2,pKa3 and the equivalence points of H3PO4
Post by: Chimystlearner on October 10, 2018, 02:20:11 PM

Quote from: Chimystlearner on October 08, 2018, 01:02:24 PM

According to this table: (Note that it is a triprotic acid) So there will be 3 different pKa and 2 equivalence points. Relevant dates:
H3PO4 is at 0,1M and NaOH 1M
H3PO4(L)   NaOH(L)   pH   Total Volume
0,1                     1,61   0,1
0,1   0,001          1,67   0,101
0,1   0,002          1,76   0,102
0,1   0,003          1,85   0,103
0,1   0,004          1,97   0,104
0,1   0,005          2,04   0,105
0,1   0,006          2,08   0,106
0,1   0,007          2,37   0,107
0,1   0,008          2,58   0,108
0,1   0,009          2,88   0,109
0,1   0,01                  3,68   0,11
0,1   0,011          5,5   0,111
0,1   0,012          6,06   0,112
0,1   0,013          6,29   0,113
0,1   0,014          6,5   0,114
0,1   0,015          6,67   0,115
0,1   0,016          6,84   0,116
0,1   0,017          7,01   0,117
0,1   0,018          7,27   0,118
0,1   0,019          7,56   0,119
0,1   0,02                  7,7   0,12
0,1   0,021         10,24   0,121
0,1   0,022         10,73   0,122
0,1   0,023         10,99   0,123
0,1   0,024         11,17   0,124
0,1   0,025         11,31   0,125
0,1   0,026         11,41   0,126
0,1   0,027         11,54   0,127
0,1   0,028         11,65   0,128
0,1   0,029         11,72   0,129
0,1   0,03                 11,82   0,13
0,1   0,031         11,88   0,131
0,1   0,032         11,95   0,132
0,1   0,033         12,02   0,133
0,1   0,034         12,08   0,134
0,1   0,035         12,12   0,135
0,1   0,036         12,13   0,136
0,1   0,037         12,18   0,137
0,1   0,038         12,21   0,138
0,1   0,039         12,24   0,139

I´m an undergraduate student trying to find the values of the dates given without previously knowing either the Ka from H3PO4.

Title: Re: Find pKa1,pKa2,pKa3 and the equivalence points of H3PO4
Post by: Borek on October 10, 2018, 06:12:01 PM

Quote from: Chimystlearner on October 10, 2018, 02:20:11 PM

I´m an undergraduate student trying to find the values of the dates given without previously knowing either the Ka from H3PO4.

That's still hardly an attempt at solving the problem.

What do you know about titration curves? Do they have some specific points, other than the equivalence?

Have you tried to plot the curve? Calculate the acid concentration?

Title: Re: Find pKa1,pKa2,pKa3 and the equivalence points of H3PO4
Post by: Arkcon on October 10, 2018, 06:28:15 PM

Why would you quote your own posting, especially when that posting is a list of numbers?  Try using Excel to graph that table, what do you see?

Title: Re: Find pKa1,pKa2,pKa3 and the equivalence points of H3PO4
Post by: Babcock_Hall on October 11, 2018, 12:38:21 PM

From the graph, one could make tolerable initial estimates IMO.