Identifying Unknown Ions and Cations

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Objective: To successfully separate and identify all three unknown cations, found in a mixture and belonging to one of two specific groups (2 from one and 1 from the other). In order to do this we will be using various tests and reactions and observing the effect they had on our solution.

Materials: Pasteur pipetsBunsen Burners
Stirring rodsExcess reagents
Hot platesSample QA unknown 101-5.7

Table of steps and observations:

Step/Test |Observation |Inference | |2-1 Adjustment of pH |Upon adding 5 drops of HCl no change was observed |The solution became acidic, seperating the group 2 sulphides | |2-2 Precipitation of Group 2 Sulphides |After adding thioacetamine and heating, the mixture turned orange after 5mins, and then formed a bright orange precipitate around 15mins.

After first centrifuge the solution came out pale orange.

The second heat and centrifuge produced very little precipitate. |The orange colour in the solution may indicate a presence of Cadmium (Cd2+)

Most of the Group 2 ions in solution were precipitated out in reaction.

Nearly complete reaction was obtained. | |2-3 Separation and Detection of Bismuth |After heating with HNO3 added a yellow gelatinous substance appeared.

After NH3 was added to create a basic solution no cloudy white precipitate was observed. |This was elementary sulphur and was discarded.

No bismuth present. | |2-4 Identification of Copper |No blue colour observed in the solution for 2-3. |No copper present. | |2-5 Identification of Cadmium |When thioacetamine was added and the solution was heated, a yellow precipitate formed. |The yellow precipitate indicates that cadmium is present in the solution. | |3-1 Isolation of Group 3 Cations |HNO3 and H2O were added to the solution from 2-2 and heated to evaporate down to 1-2mL and expel all H2S. When tested with acetate paper after 18mins it did not change colour. |No more H2S was given off because the acetate test was negative. |...
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