CHM 2045C Module Five Sample     Name:_______________

 

Module Four Part N Mixture/MultiStep Problem  8 points

 

A mixture of Sodium chloride and sodium bromide, weighing 3.5084 grams was dissolved and treated with enough Silver nitrate to precipitate all the chloride and bromide as silver chloride and silver bromide.   The washed precipitate was treated with KCN to solubilize the silver and resulting solution was electrolyzed.  The equations are:

 

        NaCl      +    AgNO3     ---->   AgCl    +   NaNO3

 

        NaBr      +    AgNO3     ---->   AgBr    +   NaNO3

 

        AgCl       +   2 KCN      -----> KAg(CN)2   +    KCl

 

        AgBr       +   2 KCN      -----> KAg(CN)2   +    KBr

 

4 KAg(CN)2   +    4   KOH   ------>     4 Ag    +    8 KCN      + O2   +   2 H2O

 

After the following step was complete the deposit of metallic silver weighed 5.502 grams.   What was the composition of the initial mixture?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ANSWER:  65.23%  NaCl   34.77 % NaBr