Chemistry/Analysis of Solutions Marking Scheme

MARKING SCHEME FOR SCIENCE 10 LAB ANALYSIS OF  SOLUTIONS

MAXIMUM = 8

DATA:

(1) Table I :  Results of Mixing KNOWN Solutions

Table II :  Results of Mixing UNKNOWN Solutions (1)

CONCLUDING QUESTIONS 1.	Show the results of your analysis by filling in the table below. (2.5)

2.	You have been hired to analyze a water sample. The person bringing you the sample tells you that it is one of the following samples:
 * a solution containing only Pb2+
 * a solution containing only Ag+, or
 * a solution contain neither Pb2+ nor Ag+,

but she does not know which sample it is. How could you use the results of your experiment to find what is in the sample you have been given?

(1.5) Add KI: 	if the solution turns pale yellow, the sample contains Ag+
 * if the sample turns bright yellow, the sample contains Pb2+
 * if the sample does not turn pale or bright yellow, the sample contains neither Ag+ nor Pb2+.

3. Why isn’t it necessary to mix the chemical combinations for the grey squares in Data Table I?

(1) An ion won’t react with itself or no reaction will occur.

4. Why is it unnecessary to mix BOTH the solutions in the upper triangle of 15 squares AND the lower triangle of 15 squares in Data Table I? In other words, why is it permissible to copy the results from the upper set of 15 squares into the “kitty corner” set of 15 squares below the grey band?

(1) The upper triangle might refer to adding A to B, while the lower triangle would refer to adding B to A. The two mixtures are the same and therefore do not need to be repeated.