WAEC 2023 Exams Preparatory Class on the Analysis of Lead Trioxonitrate V

  

  The analysis of lead trioxonitrate V can be done using different tests to help identify the ions present in the compound.

   This tutorial class will be based on one of the several methods of testing for the ions in lead trioxonitrate V salt.

 Procedure:

  Put some lead trioxonitrate V salt sample into a test tube and add about 10 cm³ of distilled water, then shake very well to dissolve. Divide the solution into five portions.

1.     To the first portion, add dilute sodium hydroxide solution in drops then excess. A white precipitate which is soluble in excess dilute sodium hydroxide indicates that zinc ions, aluminium ions or lead ions might be present in the solution.

 

2.      Add aqueous ammonia in drops then in excess to the second portion. A white precipitate is formed which is insoluble in excess aqueous ammonia indicating that zinc ions are absent and aluminium ions or lead ions might be present.

 

3.     To the third portion, add dilute hydrochloric acid and warm gently. A white precipitate which is soluble when it is hot and insoluble when it is cold indicates that lead ions are likely to present.

 

4.     To the fourth portion, add potassium iodide solution. A yellow precipitate confirms the presence of lead ions in the solution.

 

5.     To the fifth portion, add concentrated tetraoxosulphate (VI), H₂SO₄, acid and add copper turning then warm gently. The liberation of a gas with a strong unpleasant smell confirms the presence of trioxonitrate V ion (NO₃^-).

 

Example Question

Q is a sample of an inorganic compound carry out the following tests on Q and record your observation and inference.

	Test	Observation	Inference
1	Q +distilled water and divide into five portions		Coloured ions are absent. K+, Na+, NH+ or NO3- likely present
2	To the first portion from (1)above, add dilute NaOH solution in drops then in excess	A white precipitate which is soluble in excess
3	To the second portion from (1) above, add aqueous ammonia in drops then in excess		Zn2+ absent. Pb2+ or Al3+ is likely to be present.
4	To the third portion from (1) above, add dilute HCl acid and warm gently		Pb2+  likely present
5	To the fourth portion from (1) above, add potassium iodide solution	A yellow precipitate formed
6	To the fifth portion from (1) above, add H2SO4 and copper turning then warm gently.		NO3- confirmed

 

 

 

 

 

 

 

 

 

 

 

 

 

Answer

 

	Test	Observation	Inference
1	Q +distilled water and divide into five portions	Soluble and gives a clear solution	Coloured ions are absent. K+, Na+, NH+ or NO3- likely present
2	To the first portion from (1)above, add dilute NaOH solution in drops then in excess	A white precipitate which is soluble in excess	Zn2+, Pb2+ or Al3+ Likely present.
3	To the second portion from (1) above, add aqueous ammonia in drops then in excess	A white precipitate which is insoluble in excess	Zn2+ absent. Pb2+ or Al3+   is like to be present.
4	To the third portion from (1) above, add dilute HCl acid and warm gently	A white precipitate which soluble when hot and insoluble when cold	Pb2+  likely present
5	To the fourth portion from (1) above, add potassium iodide solution	A yellow precipitate formed	Pb2+  confirmed
6	To the fifth portion from (1) above, add H2SO4 and copper turning then warm gently.	A brownish gas with a strong unpleasant smell liberated.	NO2  liberated NO3- confirmed