Description

Below is the experiment

Experiment 8: Identification of metal ions and inorganic compounds in aqueous solution

Introduction:

  Inorganic qualitative analysis is the unambiguous identification of cations and anions present in the solutions. The techniques used in qualitative analysis can be vary in complexity, depending on the nature of the samples. (Encyclopeadia Britannica 2014) Unique tests for all ions in the possible presence of all others are virtually impossible to devise because different cations give similar results to each other. Therefore, a solution is treated to separate ions into smaller groups to identify the metal ions.

  Next, selective precipitation is the most common way to subdivide cations into smaller groups, in which a small group of cations is precipitated chemically. The precipitate formed can be separated physically from the remaining cations in the solution by centrifuging. The precipitate which is the insoluble solid settles out and the solution (supernatant liquid) is decanted into another container. As a result, the initial large group can be divided into smaller groups until a definitive test can be performed to verify the presence or absence of each specific cation.

  Besides, it is important to know that many chemical reactions do not go to completion. The difference to which a reaction occurs depends on the magnitude of the equilibrium constant,  for the reaction and the concentrations of reagents present. According to Le  principle, the equilibrium can be shifted by adding or removing reagents and by altering the physical conditions such as temperature of the solutions.

  In this experiment, various types of reagents are used so that the precipitation presents. The techniques stated above are used in order to identify the metal ion present in an unknown solution. It is also employed to identify an unknown inorganic compound in this experiment by observing the colour changes of the solution when it reacts with other reagents. The reagents are dissolved sparingly so that the soluble compounds or complex particular ions will not interfere with tests for other ions.

Objective:

To identify the inorganic compounds by their chemical reactions.

Apparatus Needed:

Test tubes, droppers

Chemicals Needed:

0.1M Ba (NO3)2 solution, 0.1M Mg(NO3)2  solution, 0.1M Pb(NO3)2 solution, 0.1M Co(NO3)2  solution, 0.1M Fe(NO3)3  solution, 0.5M (NH4)2SO4， 0.5M NH4SCN, 0.5M NaOH solution, 4M NaOH solution, 0.5M NH3(aq) solution, 4M NH3(aq) solution, 0.5 M CuSO4  solution, 0.5M Pb(NO3)2  solution, 0.5M Zn(NO3)2  solution, 0.5 M BaCl2

Procedures:

A. Identification of metal ions in aqueous solution

1.        Five dry test tubes were obtained. The test tubes 1, 2, 3, 4 and 5 were labelled.

2.        Four drops of 0.1 M Ba (NO3)2 solution was added to test tube 1, four drops of 0.1M Mg (NO3)2 solution was added to test tube 2, four drops of 0.1 M Pb (NO3)2 solution was added to test tube 3, four drops of 0.1 M Co (NO3)2 solution was added to test tube 4, and four drops of 0.1M Fe (NO3)3 solution was added to test tube 5.

3.        The color of the metal ion solution in each test tube was recorded in the results section.

4.        Four drops of 0.5M (NH4)2SO4 were added to each of the five test tube in step 2.The test tube was carefully observed for any evidence of reaction. The observations were recorded in the table on the results section. The formulas of the substances formed in this reaction were written in the results section. If no reaction occurs, ‘no change, NC’ was written.

5.        The contents of the five test tubes were emptied into the waste container.

6.        Steps 1 and 2 above were repeated, four drops of each metal nitrate solution was added to separate clean, dry test tubes.

7.        Four drops of 0.5M NH4SCN was added to each of the five test tubes from steps 6.The test tubes were carefully observed for any evidence of reaction. The observations were recorded in the table on the data sheet. The contents of the five test tubes were emptied into the waste container.

8.        Steps 1 and 2 were repeated, four drops of each metal nitrate solution were added to separate clean, dry test tubes.

9.        Four drops of the freshly prepared 0.5M NaOH solution (limited OH- ions) was added to each of the five test tubes in step 8. The test tubes were carefully observed for any reaction. The observations were recorded in the results section. The contents of the five test tubes were emptied into the waste container.

10.     Steps 1 and 2 were repeated, four drops of each metal nitrate solution were added to separate clean, dry tubes.

11.     Four drops of 4M NaOH solution (excess OH- ions) were added to each of the five test tubes in step 10. The test tubes were carefully observed for any evidence of reaction. The observations were recorded in the results section. The contents of the five test tubes were emptied into the waste container.

12.     Steps 1 and 2 were repeated, four drops of each metal nitrate solution was added to separate clean, dry test tubes.

13.     Four drops of the freshly prepared 0.5M NH3(aq) solution were added to each of the five test  tubes in step 12. The test tubes were carefully observed for any evidence of reaction. The observations were recorded on the data sheet. The contents of the five test tubes were emptied into the waste container.

14.     Steps 1 and 2 were repeated, four drops of each metal nitrate solution were added to separate clean, dry test tubes.

15.     Four drops of 4M of NH3(aq) solution was added to each of the five test tubes in step 14. The test tubes were carefully observed for any evidence of reaction. The observations were recorded in the table in the results section. The contents of the five test tubes were emptied into the waste container.