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Chapter 12: Q8P-g (page 283)

Consider the titration of 25.0 mL of 0.020 0 M MnSO4 with 0.010 0 M EDTA in a solution buffered to pH 8.00. Calculate pMn2+ at the following volumes of added EDTA and sketch the titration curve:

(a) 0 mL (b) 20.0 mL (c) 40.0 mL (d) 49.0 mL (e) 49.9 mL (f) 50.0 mL (g) 50.1 mL(h) 55.0 mL (i) 60.0 mL

Short Answer

Expert verified

(g) For 50.1 mL the value of pMn2+is 8.69.

Step by step solution

01

Introduction

Equations and data obtained in order to proceed for calculation are as follows

Titration  Reaction: Mn2++EDTA⇌MnY2−Kf=1013.89At   pH   8  αY4−=4.2×10−3 Table 12−1

02

Determine equilibrium constant

Kf'=αY4−×Kf=4.2×10−3×1013.89=3.3×1011

Equivalence point=50 mL

03

Determine the value of pMn2+

Past equivalence point (50.1mL) we need to calculate the metal concentration

There is 0.1 mL of Excess EDTA

EDTA= 0.125+50.1×0.01M=1×10−5MMnY2−= 2525+50.1×0.02M=6.65×10−3M

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Most popular questions from this chapter

How many milliliters of 0.050 0 M EDTA are required to react with 50.0 mL of 0.010 0 M Ca2+? With 50.0 mL of 0.010 0 M Al3+?

A 25.00-mL sample containing Fe3+ and Cu2+ required 16.06 mL of 0.050 83 M EDTA for complete titration. A 50.00-mL sample of the unknown was treated with NH4F to protect the Fe3+. Then Cu2+ was reduced and masked by thiourea. Addition of 25.00 mL of 0.050 83 M EDTA liberated Fe3+ from its fluoride complex to form an EDTA complex. The excess EDTA required 19.77 mL of 0.018 83 M Pb2+ to reach a xylenol orange end point. Find [Cu2+] in the unknown.

Indirect EDTA determination of cesium. Cesium ion does not form a strong EDTA complex, but it can be analyzed by adding a known excess of NaBiI4 in cold concentrated acetic acid containing excess NaI. Solid Cs3Bi2I9 is precipitated, filtered, and removed. The excess yellow is then titrated with EDTA. The end point occurs when the yellow color disappears. (Sodium thiosulfate is used in the reaction to prevent the liberated from being oxidized to yellow aqueous I2 by O2 from the air.) The precipitation is fairly selective for Cs+. The ions Li+, Na+, K+, and low concentrations of Rb+ do not interfere, although Tl+ does. Suppose that 25.00 mL of unknown containing Cs+ were treated with 25.00 mL of 0.08640 M NaBiI4 and the unreacted Bil4-required 14.24 mL of 0.0437 M EDTA for complete titration. Find the concentration of Cs+ in the unknown.

Give three circumstances in which an EDTA back titration might be necessary

A 50.0-mL solution containing Ni2+ and Zn2+ was treatedwith 25.0 mL of 0.045 2 M EDTA to bind all the metal. The excess unreacted EDTA required 12.4 mL of 0.012 3 M Mg2+ for complete reaction. An excess of the reagent 2,3-dimercapto-1-propanol was then added to displace the EDTA from zinc. Another 29.2 mL of Mg2+ were required for reaction with the liberated EDTA. Calculate the molarity of Ni2+ and Zn2+ in the original solution
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