2. APPLYING THE SCIENTIFIC METHOD TO SOLVE A CHEMICAL PROBLEM
5 Solution Unknown Lab
APPLYING THE SCIENTIFIC METHOD TO SOLVE A CHEMICAL PROBLEM

3. 5-Solution Unknown Lab
Purpose: To use the scientific method to determine the relationship between a set of numbered solutions and a set of lettered solutions.
Safety:
Wear safety glasses.
Avoid contact with chemicals. Wash your hands after the experiment.

4. Which letters match with which numbers?
Initial Observations: All pipettes contain cl,c liquids A 1 B 2 C 3 D 4 E 5

5. Types of observations Clear, colorless (cl,c) clear, yellow liquid
white precipitate (ppt)
Yellow ppt

6. Data Table: Abbreviations: cl = clear, c = colorless, NR = no reaction, ppt = precipitate
LETTERS:
Initial observations: All chemicals are c,cl liquids. A B C D E X

7. Data Table for Lettered Solutions
Initial Observations: All lettered solution are clear and colorless liquids.
COMBINATION TESTED
Final Observations
A + B
A + C
A + D
A + E
B + C
B + D
B + E
C + D
C + E
D + E

8. Data Table: Abbreviations: cl = clear, c = colorless, NR = no reaction, ppt = precipitate
LETTERS:
Initial observations: All chemicals are c,cl liquids. 1 2 3 4 5 X

9. Data Table for Numbered Solutions
Initial Observations: All numbered solutions are clear and colorless liquids.
COMBINATION TESTED
Final Observations

10. Example Practice: 4 Solution Unknown
Initial Observations: All pipettes contain cl,c liquids A 1 B 2 C 3 D 4

11. Data Table – 4 solution unknown
Test Cross
Outcome
A + B
Purple ppt
A + C
Green Clear
A + D
No Rxn
B + C
White ppt
B + D
C + D
Test Cross
Outcome
1 + 2
Green Clear
1 + 3
White ppt
1 + 4
2 + 3
No Rxn
2 + 4
Purple ppt
3 + 4

12. Data Table – 4 solution unknown
Test Cross
Outcome
A + B
Purple ppt
A + C
Green Clear
A + D
No Rxn
B + C
White ppt
B + D
C + D
Test Cross
Outcome
1 + 2
Green Clear
1 + 3
White ppt
1 + 4
2 + 3
No Rxn
2 + 4
Purple ppt
3 + 4
Purple ppts: A + B = 2 + 4;
A = 2, B =4, C =1, D =2
Green, clear: A + C = 2 + 1;

13. A = 2, B =4, C =1, D =2 is a hypothesis
Key Aspect of Science – hypothesis must be tested by experiments.
A hypothesis must have predictive power – it must predict the outcome of experiments that have not yet been carried out.
Example: If A + B = purple ppt and A =2, then 2 + B = purple ppt. Test 2 + B to see if purple ppt is produced.

14. 5 – Solution Unknown 1) Combinations which produce brown ppt: + = +
2) Combinations which produce yellowish white ppt: =
3) Two Combinations which produce magenta pink: =
AND =
HYPOTHESIS: A = B = C = D= E =

15. TESTING HYPOTHESIS WITH NUMBER-LETTER CROSSES
HYPOTHESIS MUST BE TESTED EXPERIMENTALLY:

16. Questions
1. In generating your hypothesis, what color was the most useful to begin the matching process and why?
2. Why is it important to have test crosses; that is, what purpose do they serve?