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1.5 Gas Test Video

Dear students, this video help you to understand the gast test.

1.5 Gas Test

Gas	Example of Preparation	Test
Oxygen (O2)	Decomposition of hydrogen peroxide H2O2 -----> H2O + ½O2(g) Thermal decomposition of some metallic oxides 2PbO -----> 2Pb + O2(g)	Ignites a glowing splint since oxygen supports combustion
Hydrogen (H2)	acid + metal -----> salt + hydrogen gas 2HCl + Zn -----> ZnCl2 + H2(g) active metal + water -----> hydroxide + hydrogen gas Ca(s)+ 2H2O--->Ca(OH)2+ H2(g)	"Pop Test" : a lit taper will produce an audible "pop" when placed in hydrogen gas
Carbon dioxide (CO2)	acid + carbonate -----> salt + water + carbon dioxide 2HCl+CaCO3-->CaCl2+H2O+CO2(g) Thermal decomposition of some carbonates CuCO3 -----> CuO + CO2(g)	When CO2(g) is bubbled through colourless limewater (Ca(OH)2(aq))the limewater turns milky due to the formation of a calcium carbonate (CaCO3(s)) precipitate. When CO2(g) is bubbled through Ba(OH)2(aq) a white precipitate of BaCO3 forms.
Nitrogen dioxide (NO2)	Thermal decomposition of some nitrates 2Ni(NO3)2--->2NiO + O2+ 4NO2(g) 2Pb(NO3)2--->2PbO + O2+4NO2(g) Less active metals + nitric acid -----> nitrate + water + nitrogen dioxide Cu + 4HNO3 ---> Cu(NO3)2 + 2H2O + 2NO2(g)	Nitrogen dioxide is a red-brown gas which is soluble in water and has a pungent odour.
Sulfur dioxide (SO2)	Combustion of sulfur S(s) + O2 -----> SO2(g) Sulfites + acid -----> water + sulfur dioxide SO32- + 2H+ -----> H2 + SO2(g) Hot concentrated sulfuric acid + copper 3H2SO4 + Cu(s) --->Cu2++2HSO4-+2H2O +SO2(g)	SO2(g) is bubbled through hydrogen peroxide solution (H2O2) to produce sulfuric acid (H2SO4). The addition of barium chloride solution (BaCl2(aq)) to this solution results in a precipitate of barium sulfate (BaSO4(s)). SO2(g) passed through a concentrated, acidified solution of potassium dichromate (K2Cr2O7) causes the dichromate solution to change colour from orange to green due to the formation of chromium (III) ions (Cr3+).
Hydrogen sulfide (H2S)	sulfide + acid -----> salt + hydrogen sulfide FeS(s) + 2HCl ---> FeCl2 + H2S(g)	H2S is often referred to as "rotten egg gas" as it smells just like rotten eggs! H2S(g) is passed through a solution of zinc chloride (ZnCl2) and a white precipitate of zinc sulfide forms (ZnS(s)). Pass H2S(g) over a damp filter paper impregnated with lead (II) nitrate (Pb(NO3)2), the paper turns black as lead (II) sulfide (PbS(s)) forms.
Chlorine (Cl2)	MnO2(s) + 2Cl- + 4H+ --->Mn2+ + 2H2O + Cl2(g) Electrolysis of molten sodium chloride (NaCl) 2NaCl -----> 2Na(Hg) + Cl2(g) (Na(Hg) is a mercury amalgam of sodium metal since sodium is slightly soluble in mercury but doesn't react with mercury as it does with other solvents like water.)	Cl2(g) is a pale yellow-green gas which bleaches coloured materials and has a characteristic choking odour.

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1.4 Qualitative Analysis

Next we are going to learn about qualitative analysis. What is qualitative analysis? Qualitative analysis is a Techniques for identify species in chemistry. It involves several techniques such as

• Physical properties (colour and solubility)
• Gas test
• Action of heat
  
• Cation Test
• Anion Test
• Confirmatory Test

8.2 (a) meaning of qualitative analysis

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