Carrying out test-tube reaction to identify cations and anions

Question 1

ammonium

Answer 1

• method
  
  • warm with sodium hydroxide soln in test tube
  • test gas produced with moist red litmus/universal indicator paper
• result
  
  • pungent-smelling gas changes paper to blue
  • alkaline ammonia gas
• or
  
  • test the gas produced with glass rod dipped in conc HCl
  • white fumes of ammonium chloriide

Question 2

Mg²⁺

Answer 2

• method
  
  • make soln of the compund and add a few drops of sodium hydroxide
  • then add excess sodium hydroxide
• result
  
  • white ppt

Question 3

Ca²⁺

Answer 3

• method
  
  • dip nipchrome wire in conc HCl then into sample
  • place in bunsen burner
• result
  
  • brick-red flame

Question 4

Ba²⁺

Answer 4

• method
  
  • dip nipchrome wire in conc HCl then into sample
  • place in bunsen burner flame
• result
  
  • green flame

Question 5

Sr²⁺

Answer 5

• method
  
  • nipchrome wire in conc HCl then into sample
  • place in Bunsen burner flame
• result
  
  • red flame

Question 6

Cl^-

Answer 6

• method
  
  • make soln of compound
  • add acidified silver nitrate solution
  • followed by aqueous ammonia
• reuslt
  
  • white ppt
  • dissolves in aqueous ammonia to give colourless soln

Question 7

Br^-

Answer 7

• method
  
  • make a soln of compound
  • add some acidified silver nitrate soln
  • followed by aqueous ammonia
• result
  
  • cream ppt
  • insoluble in dilute aqueous ammonia
  • dissolves in conc aqueous ammonia to give colourless soln

Question 8

I^-

Answer 8

• method
  
  • make soln of compound
  • add some acidified silver nitrate soln
  • followed by ammonia soln
• result
  
  • yellow ppt
  • insoluble in dilute and conc aqueous ammonia

Question 9

sulfate, SO₄^2-

Answer 9

• method
  
  • make soln
  • add barium chloride
• result
  
  • white ppt

Question 10

OH-

Answer 10

• method
  
  • warm with some solid ammonium salt
  • test gas produced with red litmus paper/glass rod dipped in HCl
• result
  
  • pungent gas (ammonia) released
  • changes red litmus to blue
  • produces white fumes with conc HCl
• reverse of test for ammonium

Question 11

carbonate, CO₃^2-

Answer 11

• method
  
  • add some dilute ntric acid
  • test gas prdocued with lime water
• result
  
  • effervescence
  • and the gas changes colourless limewater milky