Qualitative Analysis Lab
Qualitative Analysis of Cations
Short Overview
The most common cations have been placed into five groups based upon solubility in aqueous solutions when different reagents are added. The reactions which occur are useful in identifying the presence of these cations in unknown samples. The process of identifying the cations is called qualitative analysis. The purpose of this experiment is to identify which cations are present in unknown solutions.
A data sheet was not prepared for this experiment, so you must record your observations in the lab notebook as you do the experiment. This experiment will last several laboratory periods.
A. Theory Read Sections 17.6 - 17.7 ( pp. 756-760) and Table 4.1 (p. 127) in your textbook …show more content…
The solution in the test tube from step 9 contains the Cu2+ ions. To this solution, add 1 mL of 3% H2O2. Boil the solution down to a volume of about 1 mL. Now add 6 M HCl until the pH reaches 0.5. Once the pH has been lowered to 0.5, add 1 mL of 1 M CH3CSNH2 (thioacetamide) to the test tube.
15. Heat the test tube in a BWB under a fume hood for at least 5 minutes. The reactants will generate H2S , a toxic gas, in small quantities, so you should avoid breathing the fumes as much as possible. The reaction will produce a precipitate which will get darker as heating continues. Continue heating for two minutes after the color has stopped changing. Put a cork stopper on the test tube and cool it under the water tap; then allow the test tube stand for a minute or so before centrifuging.
Note: Because you have generated H2S, you must centrifuge these samples under a fume hood.
16. Decant the solution above the precipitate and transfer to a clean test tube. Add 1 mL of 1 M NH4Cl and 1 mL water to the precipitate and set …show more content…
To the solid remaining after washing, add 1 mL 6 M HCl and stir. The BaCrO4 will dissolve and produce an orange solution. Add 0.5 mL 3 M H2SO4. A white precipitate of BaSO4 confirms the presence of Ba2+.
Flame Tests Analysis of Sodium and Potassium
One of the most common methods of identifying cations is by using a flame test. The flame color is due to excitation of valence-shell electrons upon heating, followed by relaxation of the electrons with the emission of photons of light.
Sodium ion can be identified by a very intense yellow-orange flame. Potassium ion is identified by a lavender-pink flame. However, if both ions are present together, the intense flame of Na+ hides the color of the K+ flame. It is therefore necessary to use a blue cobalt glass plate to absorb the color of the sodium ion, so that the flame of potassium ion can be seen.
The ammonium ion will not interfere with the flame tests.
35. Obtain a flame test wire from the instructor. Light a bunsen burner and place the wire in the flame to clean the wire. The wire will be clean when the color of the flame above the wire is
Short Overview
The most common cations have been placed into five groups based upon solubility in aqueous solutions when different reagents are added. The reactions which occur are useful in identifying the presence of these cations in unknown samples. The process of identifying the cations is called qualitative analysis. The purpose of this experiment is to identify which cations are present in unknown solutions.
A data sheet was not prepared for this experiment, so you must record your observations in the lab notebook as you do the experiment. This experiment will last several laboratory periods.
A. Theory Read Sections 17.6 - 17.7 ( pp. 756-760) and Table 4.1 (p. 127) in your textbook …show more content…
The solution in the test tube from step 9 contains the Cu2+ ions. To this solution, add 1 mL of 3% H2O2. Boil the solution down to a volume of about 1 mL. Now add 6 M HCl until the pH reaches 0.5. Once the pH has been lowered to 0.5, add 1 mL of 1 M CH3CSNH2 (thioacetamide) to the test tube.
15. Heat the test tube in a BWB under a fume hood for at least 5 minutes. The reactants will generate H2S , a toxic gas, in small quantities, so you should avoid breathing the fumes as much as possible. The reaction will produce a precipitate which will get darker as heating continues. Continue heating for two minutes after the color has stopped changing. Put a cork stopper on the test tube and cool it under the water tap; then allow the test tube stand for a minute or so before centrifuging.
Note: Because you have generated H2S, you must centrifuge these samples under a fume hood.
16. Decant the solution above the precipitate and transfer to a clean test tube. Add 1 mL of 1 M NH4Cl and 1 mL water to the precipitate and set …show more content…
To the solid remaining after washing, add 1 mL 6 M HCl and stir. The BaCrO4 will dissolve and produce an orange solution. Add 0.5 mL 3 M H2SO4. A white precipitate of BaSO4 confirms the presence of Ba2+.
Flame Tests Analysis of Sodium and Potassium
One of the most common methods of identifying cations is by using a flame test. The flame color is due to excitation of valence-shell electrons upon heating, followed by relaxation of the electrons with the emission of photons of light.
Sodium ion can be identified by a very intense yellow-orange flame. Potassium ion is identified by a lavender-pink flame. However, if both ions are present together, the intense flame of Na+ hides the color of the K+ flame. It is therefore necessary to use a blue cobalt glass plate to absorb the color of the sodium ion, so that the flame of potassium ion can be seen.
The ammonium ion will not interfere with the flame tests.
35. Obtain a flame test wire from the instructor. Light a bunsen burner and place the wire in the flame to clean the wire. The wire will be clean when the color of the flame above the wire is