ASRJC 2022 Inorganic QA Notes

1 Anderson Serangoon Junior College Inorganic Qualitative Analysis Notes CONTENT No. Description 1. Qualitative Analysis 2. Manipulative Skills 3. Recording of Observations 4. Appearance of Unknown 5. Solubility of Salts 6. Testing of Ions 7. Separation of Ions 8. Test for Gases 9. Heating 10. Qualitative Analysis Notes Name: ___________________________ Class: ___________________________

2 1. Qualitative Analysis Qualitative Analysis is a method used to identify ions in compounds based on chemical reactions that involve:  Evolution of gas  Formation of precipitate  Colour change 1.1 Safety In addition to the general lab safety rules, the following should be observed at all times when implementing qualitative analysis experiments:  Students must wear safety goggles.  Do not touch chemicals with your hands. Wash off immediately any chemicals that comes into contact with the skin.  Note the smell of a gas by wafting it gently to the nose. Do not take in deep breath of gas.  Dispose wastes carefully. Dilute concentrated acids and alkalis before pouring them away and flush the sink with plenty of water. Dispose solid waste into waste bins, not the sink.  A test-tube holder must be used when tests involve: o warming o adding concentrated acids, alkalis and flammable reagents. Such experiments should be carried out in the fume cupboard.  When warming the mixture or burning, direct the mouth of test-tubes away from people.  Turn off the Bunsen flame when not in use. 2. Manipulative Skills 2.1 Quantity of Chemicals  Collect sufficient quantities but not in excess. The use of large quantities of a chemical often leads to a waste of time as it takes a longer time to dissolve. In addition, this may lead to wrong results, e.g. if too much of lead iodide is used, its solubility in hot water will not be observed.  The following quantities should be used, unless otherwise specified: o Solid: Enough to fill the hemisphere at the bottom of a clean and dry test-tube. The solid should be transferred by means of a clean and dry spatula into the bottom of the test-tube. o Solution: ~1 cm depth (unless otherwise specified) of a clean test-tube.

3  When testing the solubility of precipitate in excess reagent , pour out the excess precipitate until about 1 cm depth is left, before adding the excess reagent. Figure 1. How to test for solubility of precipitate formed in excess reagent 2.2 Handling of Reagents When adding reagent, dropper or tip of squeeze bottle should be held just above the mouth of the te st-tube. The tip of the dropper/bottle should not touch the sides of the test-tube. This is to avoid contamination of the bench reagents.  Add the reagent dropwise and shake until no further change in mixture or when reagent is in excess. 2.3 Gravity Filtration technique