Chemical Reactions

Burn magnesium ribbon in air

• Observation: magnesium ribbon burns with a dazzling white flame and changes into a white powder.
•  Conclusion: MgO is formed due to the reaction between magnesium and oxygen present in the  air.

Add potassium iodide solution to lead nitrate

• Observation: lead nitrate reacts with potassium iodide to give lead iodide and potassium nitrate.

• The color of the products is different from that of the reactants.

• Conclusion: Pb(NO3)2 + 2KI → PbI2 + 2KNO3.

• The change in colour is because lead iodide and potassium nitrate have been formed after the reaction. PbI2 is a yellow ppt. KNO3 is a colourless solution

Add hydrochloric acid or sulphuric acid to zinc granules

• A gas is evolved and the conical flask is warm 

• Conclusion: From this, we conclude that when a chemical reaction takes place there is a change in the state, colour, and temperature.

  
  Zn + 2HCl → ZnCl2 + H2↑ + heat 

   

  Zn + H2SO4 → ZnSO4 + H2↑ + heat

Water is added to calcium oxide

• Observation: The beaker becomes hot (exothermic reaction).

• It reacts vigorously with water.

•  Slaked lime is formed by the reaction of the combination of calcium oxide with water

• CaO(s)              +            H2O(l)              →               Ca(OH)2(aq) + heat

  
  (quicklime)                                                                 (Slaked lime)

Ferrous sulphate crystals are heated

• The green colour of the ferrous sulphate crystals has changed there is also the characteristic odour of burning sulphur.
• 2FeSO4(s) + Heat      → Fe2O3 + SO2(g) + SO3(g)

Lead nitrate is heated

• We observe the emission of brown fumes. 

• These fumes are of nitrogen dioxide (NO2). The reaction that takes place is

2Pb(NO3)2(s)        ---Heat→   2PbO(s)            +       4NO2(g)              +       O2(g)

(Lead nitrate)                           (Lead oxide)           (Nitrogen dioxide)        (Oxygen)

Electrolysis of water ( separating hydrogen and oxygen)

• The test tube containing hydrogen gas has double the volume of the test tube containing oxygen gas.
• Hydrogen gas burns with a light blue flame with a pop sound. 
• its a decomposition reaction
• 2 H2O(l) → 2 H2(g) + O2(g)

Silver chloride is kept in sunlight

• Observation: White silver chloride turns grey in sunlight.

• Conclusion: This is due to the decomposition of silver chloride into silver and chlorine by light

• 2AgCl(s)   ----Sunlight→   2Ag(s) + Cl2(g)

Iron nails are immersed in a copper sulphate solution. 

• the iron nail dipped in the copper sulphate solution in test tube A becomes brownish in colour and the blue colour of copper sulphate solution fades in test tube A. Wh

Sodium Sulphate and Barium Chloride are mixed together:

• A white substance, which is insoluble in water, is formed.
• This is a double displacement reaction shown by the equation 

Na2SO4(aq)          +     BaCl2(aq)                →          BaSO4(s)         +       2NaCl(aq)
(sodium sulphate)        (Barium chloride)                (Barium sulphate)  (Sodium chloride)