The principle content of lab 14 is chemical substance identification. The goal is to gain a better understanding of the chemical properties of different substances through qualitative and quantitative analysis. With fourteen given solutions (14 cations and 6 anions), we perform a flame test, a litmus test, and a cross-reaction test respectively, and through qualitative observations, identify the unknown components (cation and anion).
In more detail, we perform the above three tests on the following method. • Flame Test.
anion based on the color. • Litmus Test.
o Placeasmallamountofunknownsampleontothecoloredlitmuspaper. o Recordthecolorofthepaperanddeterminewhethertheunknown
sample was acidic or basic (or undetermined). • Cross-reaction Test.
o Reacteachunknownsolutionwithanotheruntilallthepossiblepairings take place.
o Recordtheresultsofthereactionsanddeducewhichcationsandanions might be present based on the chemical properties exhibited during the reactions.
Finally, we make our deduction and conclusions of the composition of given solutions.
The procedures were listed in General Chemistry Lab Manual by Dr. Meishan Zhao and experimental process was recorded and provided.
Table 1. General Observation
Solution Color Solution Smell
Strong ammonia smell
Table 2. Flame Test Result
Persistent silver white
The flame test results are as follows:
11 12 13 14
Strong white bright Persistent orange
Orange-brown Persistent crimson red
Strong carmine red, violet by blue cobalt glass Persistent green
Strong silver white Strong, persistent yellow
Lilac/weak violet, reddish by cobalt blue glass
As we know all the cations in the fourteen solutions are different, we can determine some of them now through flame test, color, and odor.
[Determine cations here]
Write your reasoning and fill the table below.
Cations for solutions
Solution # 1
The results of litmus test are as follows.
Table 3. pH Test Results
Neutral Strongly Acidic
Neutral Acidic Basic Neutral Acidic Acidic Basic Neutral Neutral
Strongly Basic Acidic
The results of different solutions reacting together are as follows.
Table 4. Well Plates Cross Reactions (precipitation and other observations)
Solution 1 2 3 4 1
Bubbles White Orange
White Brown White
Blue Soln. Cloudy
Cloudy Light Blue
9 10 11 12
In this section you should:
1. list what observations led to the compound identification.
2. With each observation, if there is one, you should write a balanced net ionic equation for the reaction involved.
A significant portion of the report grade will be based on the net ionic equations and your reasoning for the determination of the 14 solutions.
You may consider the following as a guideline in order to preserve your laboratory instructor’s sanity and your grade.
2. You should explain how you determined the ions in each solution. Present the explanations organized by solution number. Avoid circular arguments, e.g. “A is in solution #1 because it reacts with B in solution 2. Solution 2 contains B because it reacts with A in solution #1.”
3. For each reaction observation,you should include a balanced net ionic equation. You do not have to write out the same equation many times. For instance, if the reaction between solution #A and solution #B produced a blue precipitate, one may include the observation and balanced net equation when describing how solution #A was identified. When discussing solution #B, a reference to the equation in solution #A is enough.
4. It is helpful to number your equations for cross reference.
An example of part of the report is shown below. The phrase ‘‘solution # n’’ is abbreviated as ‘‘#n’’. The example provided here is for your reference only.
Solution #1: A+and X –
The A ions were identified from the characteristic color of the flame test. Supporting evidence comes from the lack of reaction of #1 with #2 and #3; each test yielded no precipitate. The anions in #2 or #3 would have formed a precipitate with all cations other than A, C, and E. The flame test indicates that C and E are not present.
Litmus paper indicates that solution 1 is basic. When X– is dissolved in water the resulting solution is basic. No ppt. was formed when #1 was reacted with #2 and #3. This is also consistent with X- as the anion since BX2 and GX are soluble.
Net ionic reaction:
Solution #2: B2+ and Y2
X- +H2O OH-+HX.
When #2 reacts with #4, a green ppt. is formed. This ppt. is B(OH)2 based on its color and the identification of OH as the anion in #4,
B2+ (aq) + 2OH- (aq) ® B(OH)2 (s).
When #2 reacts with #3, red ppt. is formed. This ppt. is BZ2(s),
B2+ (aq) + 2Z- (aq) ® BZ2 (s).
When #2 reacts with #6, a white precipitate is formed (as predicted in Eq. xxx). This precipitate can be
redissolved using solution #7. This is indicative of
Solution #3: G+ and Z
... and so on ...
Y2- (aq) + M2+ (aq) ® MY(s),
We were able to identify the unknown solutions with sufficient evidence.
1. Zhao, M. “Qualitative Analysis”, General Chemistry Lab Manual. (2015).
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