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Qualitative Analysis of Ions
Najah Serrano
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Najah Serrano
Qualitative Analysis of Ions
Page 2 of 9
CHM 113 POST-LAB
Qualitative Analysis of Ions
1.
Insert ONE picture of yourself in full PPE here (
include acetic acid
). **Remember to (1) show your full body
so that we see you are wearing shoes; (2) wear your
safety glasses, buttoned lab coat and gloves; (3) cover your lower legs (socks are not optional, even in Arizona); (4) tie back long hair in a ponytail or a bun; (5) remove jewelry.
Najah Serrano
Qualitative Analysis of Ions
Page 3 of 9
2.
Complete Table 1
based on the pH Test Strip tests that you performed in Part 1
of the experiment.
Table 1: Test Strip Results of OH
-
and H
+
Solution Type
pH Test Strip Color
pH
Acid or Base?
Acetic Acid
Yellow
6
Acid
Sodium Bicarbonate
Green
8
Base
3.
Complete Table 2
based on the qualitative tests you performed in Parts 2A – 2D
in the experiment. The “indicator” in Table 2 is what you added to the known or unknown solution to test for the presence of the listed ion that resulted in the final observation. The indicator is NOT one of the 4 unknown ion solutions.
Table 2: Test Results
Solution Type Indicator Observations Initial
Final
Carbonate Ion
CO2
Clear, normal.
Bubbled up & cloudy
Sulfate Ion
BaSO4
Clear, normal.
Foamy
Phosphate Ion
Zn3(PO4)2
Clear, normal.
Clear
Calcium Ion
CaF2
Clear Cloudy, split substances
4.
For each of the ion tests for known solutions in Table 2
(Parts 2A – 2D in the experiment), what type (or class) of reaction
occurred?
Hint: Refer to the reaction classes discussed in Sections 4.2 and 4.3 in your text.
CO
3
2-
_________________A CO2 rxn (bubbles formed)___________________
SO
4
2-
_______________Precipitation Rxn_____________________
PO
4
3-
_____________Precipitation Rxn_______________________
Ca
2+
________________Precipitation Rxn____________________
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Najah Serrano
Qualitative Analysis of Ions
Page 4 of 9
5.
In this lab, you performed numerous qualitative tests (results are in Tables 1 and 2 above) that were then used to determine the identity of an unknown ion in solution. Fill in the table below
with the results of your tests on your unknown solution. Note: The unknown solution can only contain ONE of the three ions (carbonate, sulfate, or phosphate)
. Only one of the tests should be positive
.
To have a positive result, the observation should match the observation you noted in Table 2 for that particular test.
Also, prior to testing, the unknown solution should be clear; if it is cloudy you may get inaccurate results Table 3: ‘Determination of Unknown’ Results
Carbonate Ion Test Sulfate Ion Test Phosphate Ion Test Observations
Clear
Cloudy
Clear
Result:
Positive or
Negative?
Negative
Positive
Negative
6.
Considering your observations for a positive result (indicated in Question 3) and your results
for the unknown solution in Question 5, how would you know if a qualitative test was
negative for an ion? Use one of your negative results from Table 3 compared to a positive result from Table 2 as an example to explain (in 2 - 3 sentences).
For a qualitative test to be negative for ions, the product of the reaction should not make a precipitate. I know this because during my carbonate ion test, the resulting product bubbled up and thus became a positive ion. A precipitate reaction can not result in bubble formations.
7.
What is the identity of the ion in the unknown solution? Explain (in 2 – 3 sentences) using your results from Table 3 as evidence.
Unknown ion __________A Sulfate ion_________________
The sulfate ion was the only mixture that became cloudy by the end of the experiment. The reaction created a precipitate as well.
Najah Serrano
Qualitative Analysis of Ions
Page 5 of 9
Najah Serrano
Qualitative Analysis of Ions
Page 6 of 9
8.
Identify and discuss TWO
sources of error (
using 2 -3 sentences each
) for this experiment.
NOT an acceptable source of error—be specific!)
Error Source #1: measurements
Error Source #1: test tube contamination
How to mitigate error: Throughly cleaning out the test tubes suring the experiment can help mitigate this issue of cross contamination. Quick rinses do not suffice. Also, measurements such as the ½ tsp should be as precise as
possible. A mountain of product (Epsom salts) is more than needed for the lab.
9.
Identify the equations
below as a molecular equation (
M
), a complete ionic equation (
CI
), OR a net ionic equation (
NI
).
a.
__M__
AgNO
3
(aq) + NaCl
(aq) →
AgCl (s) + NaNO
3
(aq)
b.
__M__
Na
2
CO
3
(aq) +2 HCl (aq) →
2 NaCl (aq) + CO
2
(g) + H
2
O (l)
c.
__NI__
Pb
2+
(aq)
+ S
2- (aq) →
PbS (s)
d.
__CI__
Ca
2+
(aq) + 2 Cl
-
(aq) + 2 Na
+
(aq)
+ CO
3
2-
(aq) →
CaCO
3
(s) + 2Na
+
(aq) + 2 Cl
-
(aq)
e.
__NI__
OH
-
(aq) + H
+
(aq) →
H
2
O (l)
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Najah Serrano
Qualitative Analysis of Ions
Page 7 of 9
10.
Imagine that the unknown solution contains aqueous ammonium sulfate, which is commonly
used in fertilizer. For the precipitation of barium sulfate after mixing aqueous ammonium sulfate solution and barium chloride solution (the reactants), write
the (1) balanced molecular equation, (2) the complete ionic equation, (3) the net ionic equation AND
identify
the spectator ions, if any. Be sure to include the correct formulas for each compound, stoichiometric coefficients, and physical states.
Hint: Refer to the solubility rules in the Introductory Materials page to determine the physical states of the products.
Molecular Equation:
BaCl2(aq)+NaSO4(aq)=BaSO4(s)+2NaCl(aq)
Complete Ionic Equation:
Ba(2+)+2Cl(-)+2Na(+)+SO4(2-)=BaSO4(s)+2Na(+)+2Cl(-)
Spectator Ions: _____2Cl-,2Cl-_______
_____2Na+,2Na+_______
NONE
Net Ionic Equation:
Ba(2+)(aq)+SO4(2-)=BaSO4(s)
Najah Serrano
Qualitative Analysis of Ions
Page 8 of 9
11.
Imagine that the unknown solution contains potassium bicarbonate, which is frequently used
as a pH buffering agent in foods and medications, and like sodium bicarbonate, will react with an acid. For the reaction between potassium bicarbonate solution and acetic acid solution (the reactants), write
the (1) balanced molecular equation, (2) the complete ionic equation, (3) the net ionic equation AND
identify
the spectator ions, if any. Be sure to include the correct formulas for each compound, stoichiometric coefficients, and physical states.
Hint: For guidance, refer to the equation shown at the beginning of Part 2 of the Procedure,
the reaction between sodium bicarbonate and acetic acid. The products for the reaction in Question 11 will be analogous to the products in the reference equation.
Molecular Equation:
K2CO3(s)+H2O(I)=2K(aq)+CO3(aq)
Complete Ionic Equation:
K2CO3(-1)+H2O=2K(+)+CO3(2-)
Spectator Ion(s): ______NONE______
______N/A______
NONE
Net Ionic Equation:
K2CO3(-1)+H2O=2K(+)+CO3(2-)
12. Putting it all together! You ordered two chemicals, calcium carbonate and sodium carbonate, but the labels fell off in transit! How could you determine, using the qualitative tests and methods you used in this lab, which chemical is which
?
Through using the qualitative tests and methods that I learned in this lab, a good indicator of which chemical is which is a repeat of the experiment above. For example, I’ll measure 2ml of both the calcium carbonate and sodium carbonate. Then I’ll add acetic acid (vinegar) and watch for whether or not the product forms a precipitate reaction. I’ll also be aware of what happens when these chemicals react with an acid (like vinegar) such as the sodium carbonate becoming a nitrate. This
Najah Serrano
Qualitative Analysis of Ions
Page 9 of 9
information can help me pinpoint which chemical is which.
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