Summary of easy ways to identify common substances in biological agents

In experimental biological reagents, there are several colorless and odorless gases such as oxygen (O₂), hydrogen (H₂), nitrogen (N₂), methane (CH₄), and carbon monoxide (CO). Identifying these common substances can be done through simple tests. Here's how you can distinguish them: 1. **Using a glowing splint**: If you insert a glowing splint into the gas container and it reignites with a brighter flame, the gas is oxygen (O₂). 2. **If the splint goes out**, the gas is likely nitrogen (N₂), as it does not support combustion. 3. **For flammable gases like H₂, CH₄, and CO**, you can ignite the gas and place a dry, clean beaker over the flame. After cooling, check for water droplets on the inside of the beaker. Then, add lime water to see if it turns cloudy. - If only water droplets form, the gas is hydrogen (H₂). - If the lime water becomes cloudy but no water droplets appear, it’s carbon monoxide (CO). - If both water droplets and cloudy lime water occur, the gas is methane (CH₄). It's important to note that while the solubility of these gases varies slightly, the differences are often too small to observe easily. Additionally, hydrogen, methane, and carbon monoxide are all flammable. The flame colors may differ—blue for hydrogen and methane, but yellow flames from sodium in glass can make it hard to tell. Therefore, checking the combustion products is more accurate. **Solubility of Acids, Bases, and Salts (Solubility Table):** - **Acids**: Most acids are soluble in water, except for silicic acid (H₂SiO₃), which is insoluble. - **Bases**: Only a few bases are soluble. These include ammonia (NH₃), sodium hydroxide (NaOH), potassium hydroxide (KOH), barium hydroxide (Ba(OH)₂), and calcium hydroxide (Ca(OH)₂). The rest are generally insoluble. - **Salts**: - Potassium salts, sodium salts, nitrates, and ammonium salts are usually soluble. - Sulfates: Barium sulfate (BaSO₄), silver sulfate (Ag₂SO₄), and calcium sulfate (CaSO₄) are either insoluble or only slightly soluble. - Chlorides: Most are soluble, except silver chloride (AgCl), which is insoluble. - Carbonates: Only potassium carbonate (K₂CO₃), sodium carbonate (Na₂CO₃), and ammonium carbonate ((NH₄)₂CO₃) are soluble. The rest are generally insoluble. **Note:** Barium sulfate (BaSO₄) and silver chloride (AgCl) are not only insoluble in water but also do not dissolve in acids, making them useful in qualitative analysis.

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