Analysis of an Unknown Chloride by Titration
Marjorie Carosiello
TL Hanna
High School
Anderson, SC
September 26, 2011
Titration is a volumetric procedure where by the identity of an unknown can be determined by adding
precise quantities of a standard solution of know concentration using a buret. The moles of the unknown
may be calculated when the endpoint is reached as the moles of the known solution equal the moles of the
unknown. This information allows the calculation of the molarity, or mass of the unknown dependant on
the circumstances.
In this lab an unknown group I chloride was titrated with 0.200 M silver nitrate, potassium chromate was
used to indicate the endpoint. The solution turned cream and then buff to indicate that all of the silver ions
had precipitated with the chloride ions and a second (red) precipitate, silver chromate began to fall out of
solution. The reactions are listed below:
Ag+ (aq) + Cl- (aq) --> AgCl(s)
2Ag+(aq) + CrO4-2(aq)
---->
Ag2CrO4 (s)
Reaction 1
Reaction 2
The unknown chloride was found to have 39.65, 38.57, 38.51 g/mol in the three samples respectively. The
conclusion of the experimenter was the identity of the unknown was potassium. The actual mass is reported
as 39.01 g/mol. The per cent error was determined to be 0.513%. This study illustrates that titration can be
effective in quantitative analysis.
Grading
Title
Author and address
Topic/question
Method
Results
Conclusion
+5
+5
+10
+25
+25
+20
points
Ea missing rxn
Ea incorrect sig dig
Ea incorrect unit
Neatness
-5
-1
-1
-10
The scale above is based on a 90 pt lab and a 10 pt prelab