A student recently reached out to me via whatsapp asking me to help with this O Level Chemistry Qualitative Analysis (Q.A) question.
I thought I’d very quickly show how to approach and solve Q.A. questions.
Lets start with A.
A turns litmus solution red –> A is an acid.
When Barium Nitrate is added (this is to test for the presence of sulfate ions), it gives a white precipitate, Barium Sulfate (which means sulfate ions are present!)
Hence A must be sulfuric acid!
and white precipitate E must be barium sulfate!
Next, let’s try to identify the gases – should be simple, afterall there are only 5!
When zinc is added to A, a gas D is produced.
Note – whenever a metal (zinc) undergoes a reaction, HYDROGEN gas will be produced! Hence D is hydrogen gas!
Gas C gives a white precipitate with limewater –> gas C must be carbon dioxide gas!
Lets go to B.
B is also an acid. (litmus turns red)
B produces potassium chloride when it reacts with F.
(note: if hydrochloric acid is used… the salt will be a metal chloride. If sulfuric acid is used, the salt will be a sulfate. If nitric acid is used, the salt will be a nitrate!)
Hence B is hydrochloric acid!
Lastly, lets try to figure out what F is.
Since B undergoes a neutralisation reaction with F, F must be a base – since its soluble, it must be an alkali!
There are only 3 commonly used alkalis (sodium hydroxide, potassium hydroxide & aq. ammonia.)
Hence F must be potassium hydroxide! (since potassium chloride is formed!)
I hope this has helped!