Problems for Precipitation Titration and to make you think about chemcial equations.

Due 5/4

1.  A 1.000 liter sample of sea water was evaporated to a small volume and treated with an excess of sodium tetraphenylboron. The precipitated tetraphenylboron was filtered and then redissolved in acetone. The analysis was completed by a Mohr titration that required 34.32 mL of 0.03875 M AgNO3. Calculate the parts per million of potassium in the sea water sample.

2.

K+ + NaB(C6H5)4® KB(C6H5)4(s) + Na+ ; Ag+ + KB(C6H5)4® AgB(C6H5)4(s) + K+

3.  The monochloroacetic acid (ClCH2COOH, MW = 94.5) preservative in a 100.0 mL sample of carbonated beverage was extracted into diethyl ether and then returned to aqueous solution as ClCH2COO- with 1 M NaOH. This aqueous extract was acidified and treated with 50.00 mL of 0.4231 M AgNO3. The reaction is

4.

ClCH2COOH + Ag+ + H2O ® HOCH2COOH + H+ + AgCl(s) .

After filtration of the AgCl titration of the filtrate and washings required 12.53 mL of an NH4SCN solution. Titration of a blank taken throught the entire process used 23.75 mL of the NH4SCN. Calculate the weight in milligrams of the ClCH2COOH in the sample.

NH4SCN + AgNO3 ® AgSCN(s) + NH4NO3 .

5.  A 4.000 gram sample of KCl and KClO4 and inert materials was dissolved in sufficient water to give 250 mL of solution. A 50 mL aliquot required 41.00 mL of 0.07500 M AgNO3 in a Mohr titration. A 25.00 mL aliquot was then treated with V2(SO4)3 to reduce the ClO4- to Cl-, following which titration required 38.12 mL of the same silver nitrate soltuion. Calculate the percent of KCl (74.56) and KClO4 (138.6) in the sample.
4 V2(SO4)3 + ClO4- + 4 H2O ® Cl-, + 8 VO2+ + 8 H+ .