Determine the volume at the equivalence point (show work on graph) Determine the

Question

Determine the volume at the equivalence point (show work on graph) Determine the pK_a, and the K_a, for the unknown acid (show work below and on the graph). If 0.392 g of unknown acid was dissolved in 50.2 mL of water, calculate the molar mass of the unknown acid. The concentration of the NaOH was 0.196 M. 4. Suppose the actual molar mass of the unknown acid was 145.3 g/mol. Calculate the percent error. Given the equilibrium Kennedy mixes 4.0 mL of 0.00200 M Fe(NO_3)_3, 3.5 mL of 0.00200 M KSCN and 2.5 mL of water. She measures equilibrium concentration of FeSCN^2+ and its value is 1.16 Times 10^-4 M. Calculate K_eq.

Explanation / Answer

V= 10.9 mL

        pKa = 4.3

3.

50.2 mL x 0.392g/ MM g/mol = 10.9 mL x 0.196 M        

Molar mass MM = 9.21 g/mol

(too low, something is wrong with the provided data)

Suppose that only an aliquot of 3.25 mL from the 50 mL acid solution was used for titration. In this case

50.2 mL x 0.392g/ MM g/mol = (50/3.25)x10.9 mL x 0.196 M

MM = 141.7 g/mol

4.

Errror % = 100 x (145.3-141.7)/145.3 = 2.5%

E.

In the mixture (final volume = 10 mL):

[FeSCN2+] = 0.000116

[Fe3+] = 0.002000M x 4mL/10mL – 0.000116 = 0.000684 M

[SCN-] = 0.002000 x 3.5mL/10 mL - 0.000116 = 0.000584 M

K = 0.000116 / (0.000684 x 0.000584) = 290

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