"Published in Newark, California, USA"
A mixture of LiBr and BaBr2 weighing 800 mg is treated 50.00 mL of 0.1879 M AgNO3 and the excess is found to require 8.76 mL of 0.3179 M KSCN for back titration, using ferric alum as indicator. What is the percentage of BaBr2 in the sample?
Solution:
If AgNO3 is added to the mixture of LiBr and BaBr2, then the chemical reactions are
Let x = be the amount of LiBr in the sample
y = be the amount of BaBr2 in the sample
Since the amount of LiBr and BaBr2 are unknown, then we need to use two equations, two unknowns.
The first working equation is
By gravimetric analysis, the amount of Br in LiBr is
By gravimetric analysis, the amount of Br in BaBr2 is
From the chemical reactions above, the second working equation is
but
Hence, the value of y which is the weight of BaBr2 is
Therefore, the percent of BaBr2 in the samples is
