lab report

Laboratory

Objectives

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Qualitative Analysis:

Identification of

Unknown Cations- Simulation

• Explore the solubility properties of salts

• Examine precipitation reactions

• Create a flowchart for determining ions present in unknown mixtures

Equipment and Materials • This worksheet

Introduction Qualitative analysis is a process used to find information regarding the composition of different species in a mixture. The analysis does not give us the amount of material present so it is not as rigorous as a quantitative analysis, but is often easier and faster to perform. In this lab you will be creating a way to identify the components in a mixture of aqueous metal ions using data gathered from several qualitative tests.

Since we cannot be in the lab, this experiment will be done for you. Images of the experiment are included in this handout, and you will need to view video of the lab to complete the final part of the worksheet.

PARTI

Data Collection 1. Set up a table in a word document for observations similar to the one shown below.

Be sure to make your grids large enough to write in your observations.

2. Following the table, there are pictures of the experiment. In each picture, a metal cation has been mixed with one of 5 reagents. Record your observations for each reaction in the table. If no reaction appears to have occurred, write NR.

Chemistry 141 I Experimental Chemistry

METAL TEST

Als . Ca2+ Co2+ Cu2+ zn2+

Fe(CN)t

PO/"°

OH-

NH 3

(NH 4 0H)

H+

1. Set up a table in a word document for observations similar to the one shown above Be sure to make your grids large enough to write in your observations.

2. Below are pictures of the experiment. In each picture, a metal cation has been mixed with one of 5 reagents. Record your observations for each reaction in the table. If no reaction appears to have occurred, write NR.

Qualitative Analysis: Identification of Unknown Cations I Laboratory 9

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Data Analysis

1. Use the observations in your data table to complete the following reactions. If no reaction was observed, write NR. Assume that precipitates are simple cation:anion ratios and have a neutral charge. Include any reactions that occur in the data section of your repor

A. Af3+

A. A1H + Fe(CN\3- ➔

B. A1H + PO 3- ➔4

C. A1H + OH- ➔

B. Ca2+

A. Ca2+ + Fe(CN\3- ➔

B. Ca2+ + PO 3- ➔ 4

C. Ca2+ + OH- ➔

C. Co2+

A. Co2+ + Fe(CN\3- ➔

B. Co2+ + PO 3- ➔ 4

C. Co2+ + OH- ➔

2. Next, steps i.-iv. listed below were completed for each ion.

i. Ten drops of fresh metal cation solution was placed in a new small test tube and 4-6 drops of HNO3 was added acidify the solution. Then 7 drops ofK3Fe(CN\ solution was added to the test tube. The image to the right shows the result of these additions for each metal ion. Use this information to fill in the flow chart on page 73. (A video of this reaction is available online.)

D. Cu2+

A. Cu2+ + Fe(CN\3- ➔

B. Cu2+ + PO 3- ➔ 4

C. Cu2+ + OH- ➔

E. Zn2+

A. Zn2+ + Fe(CN\3- ➔

B. Zn2+ + PO 3- ➔ 4

C. Zn2+ + OH- ➔

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ii. Then, a fresh 10-drop sample of the metal cation solutions were transfered into separate, new test tubes. Eight drops of NaOH solution was added to each. The result is shown in the image to the left. Use this information to fill in the appropriate part of your flow chart on page 73. (A video of this reaction is available online.)

If a precipitate formed, the sample was mixed thoroughly and centrifuged (this allows us to separate the solid from the liquid)

iii. After the samples containing the precipitate finished centrifuging, the liquid (supernatant)was decanted (poured off) into a waste beaker. Then, the solid was washed with ~ 1 mL of deionized water (using a pipette to break up any solid and ensure a good wash). The sample was then centrifuged again, and the supernatant was carefully decanted into the waste beaker, making sure not lose any solid. This wash was repeated two more times. Once the last wash was decanted, 10 drops of NH3 was added and mixed for ~60 seconds. The samples were then heated for one minute. The result of this process is shown in the image to the right. Use this information to fill in the appropriate portion of your flow chart on page 73.

iv. The process in step C above was redone to get a fresh precipitate from the hydroxide. Each sample was gently heated for less than 15 seconds. The result of this process is shown in the image to the right. This was then centrifuged and the solid separated from the liquid (however, this time the supernatant was recovered for further testing). Use this information to fill in the appropriate portion of your flow chart on page 73. (A video of this reaction is available online.)

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pp!

add NH3

sol'n

pp!

discard sol'n

sol'n pp! add H♦ • 1<3Fe(CN)6

-----'-----------" 1----------..:,__....:...,_ _ _.. Add NaOH

Al3+, Cu 2+, Zn2+,

Co2+, Ca 2+

wash in HzO pp!

sol'n

wash in HzO

pp! sol'n

Add NaOH Heat sol'n

ppt

D

add H+, K3Fe(CN)6

sol'n

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Step iStep ii

Step iii

For highlighted boxes, use spot plate results to determine expected observation

Add Na3PO4 Add Na3PO4

Chemistry 141 I Experimental Chemistry

PART II

Interpretation

We now want to consider how we might use the data and information we've just col­lected to be able to sort out a solution that contains a mixture of ions that might include anywhere from one to all five of the cations used. Consider the following questions, then use your answers to fill in the metal cations on the flowchart below. You will use this in the next part to virtually separate and verify a mixture of ions given to you.

1. Imagine that a classmate gives you a solution and tells you it contains only Ca2+ ions. Using the reaction data you observed, describe how you would prove or refute this claim in the space below.

2. Now imagine that a classmate gives you a solution claiming it contains only Zn2+ and Cu2+ ions. Using your flow chart, describe how you would prove or refute that one, two, or possibly none of those ions are present?

3. Next, imagine that a classmate gives you a solution claiming it contains only AJH and Co2+ ions. Using your flow chart and reaction data, describe how you would prove or refute that one, two, or possibly none of those ions are present in the space provided below.

4. Now pretend that you were given an unknown solution, and you followed steps in your flowchart to identify the unknown metals contained in your sample. The observations for each reaction is documented on the next page. Use this to identify the unknown metals in your solution.

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White solid

formed

White

solid

Orange solid

formed

Blue

Solution

Blue and

Pink solid

Black and

Pink solid

Black and

Pink solid

Blue and

Pink so lid

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