Design and carry out an experiment to determine the specific identity of the compound in each of eig — Qualitative Analysis Chemistry Question
Problem Context
Design and carry out an experiment to determine the specific identity of the compound in each of eight numbered vials. Each vial contains one of these ionic compounds.
BaCl2, CaCO3, Ca(OH)2, KI, NaCl, NaHCO3, Na2SO4, Pb(NO3)2
In addition to the equipment you will find at your lab station, you may use distilled water. You also have the option of choosing ONE additional reagent from this list. You may do this either before or during your experimentation.
6 M H2SO4, 6 M HCl, 6 M NaOH, phenolphthalein indicator solution
You will be asked to describe the method you developed to solve this problem.
Give a brief description of your experimental plan.
Before beginning your experiment, you must get approval (for safety reasons) from the examiner.
Model Answer
Credit was awarded for alternate, logical pathways that achieved identification of the compounds. The identifications depend on developing a logical sequence of tests that will lead to the identifications. Some type of tabular form organizes the data for clear presentation, even if a formal flow chart is not included.
Sample Plan: Many students started by adding water to each compound. Most often, H2SO4 was chosen as the extra reagent Those tests were followed by adding selected solutions of the unknown to each other to help with identification.
Record your data and other observations.
Model Answer
Sample Data:
FIRST TESTS
#1 #2 #3 #4 #5 #6 #7 #8
H2O sol insol sol sol sol insol sol sol
H2SO4 no rxn dissolves, bubbles no rxn white ppt bubbles dissolves white ppt yellow
The first set of tests allows identification of #2 as CaCO3, #5 as NaHCO3, and #6 as Ca(OH)2.
SECOND TESTS
#1 #3 #4 #7 #8
#1 – no rxn no rxn white ppt no rxn
#3 – white ppt white ppt no rxn
#4 – white ppt no rxn
#7 – yellow ppt
#8 –
The second set of tests allows identification of #1 as NaCl, #7 as Pb(NO3)2, and #8 as KI. There is still ambiguity about #3 and #4 at this point.
THIRD TESTS
#3 #4
H2SO4 no rxn white ppt
The third set of tests allows identification of #3 as Na2SO4 and #4 as BaCl2.
Identify the substance in each numbered vial, giving a brief justification for that choice.
Model Answer
Conclusion:
Identification Substance Supporting Evidence
#1 NaCl Second tests: forms a white precipitate with #7, Pb(NO3)2
#2 CaCO3 First tests: insoluble in water, dissolves and bubbles in acid
#3 Na2SO4 Third tests: no reaction with H2SO4
#4 BaCl2 Third tests: white precipitate forms
#5 NaHCO3 First tests: soluble in water, dissolves and bubbles in acid
#6 Ca(OH)2 First tests: insoluble in water, dissolves in acid
#7 Pb(NO3)2 Second tests: forms three white precipitates and one yellow precipitate
#8 KI Second tests: forms one yellow precipitate