This will be the second last blogpost on under the series of “Secrets of Acids, Bases & Salts and Qualitative Analysis revealed”, and it will be the section where either a student loves its or hates it totally.
Qualitative Analysis (QA) is essentially a chapter that is associated with the Practicals or SPAs that you do your in Chemistry Laboratories. It involves your skills in the Identification of Ions (Cations & Anions) and Gases.
Here is a screen shot on the learning outcomes that students need to know to do well in this topic:
(Click image to see properly)
Let’s get started with a typical exam-based questions that you will normally see – A Flow-Chart asking you to identify the unknowns.
(i) Identify P, Q, R , S and T. (5 marks)
(ii) In colourless solution R, identify the:
Cation Present _______________
Anion Prsent ________________
(2 marks)(iii) Identify the compound A and element B (2 marks)
(Click image to see properly. You can then save it to your computer, analyze and solve the question step-by-step)
PS: Leave me your suggested answers (as many parts as possible that you can solve) in the Comments Section below, and i will get back to you all with a Last Blogpost under this series.
“Wanting Leads to Wanting, Doing Leads to Having”
Hi there!
I aint too sure about the identities. But, here is what i think:
P: Lead iodide
Q: calcium hydroxide
S: Hydrogen gas
T: Silver nitrate
R: Zinc chloride
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sean Reply:
September 8th, 2008 at 12:16 pm
Hi Jennifer,
All is correct except T. T is a White PPT which means it is Insoluble in water.
Do note that Silver Nitrate is a Soluble Salt. In fact, all NITRATE Salts are soluble in water.
Do look through the comprehensive Power Notes that were given to you during the June Intensive Revision Bootcamp.
Look through the flowchart and determine White PPT T again.
“Complete What You Have Started!” – Sean
Sean
Master Trainer
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anoym Reply:
September 6th, 2009 at 3:28 pm
I thought nitrate ions are more reactive than chloride ions. Thus, why is there a displacement reaction?
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that’s my answer for P Q S T R too. is A calcium iodide and B zinc? email me the answer please thanks!
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sean Reply:
September 8th, 2008 at 12:17 pm
Hi Jason,
Seems like you made the same error as Jennifer. For other students that are reading this comment also, do take note cos you might be making same error also.
Jason, All is correct except T. T is a White PPT which means it is Insoluble in water.
Do note that Silver Nitrate is a Soluble Salt. In fact, all NITRATE Salts are soluble in water.
Do look through the comprehensive Power Notes that were given to you during the June Intensive Revision Bootcamp.
Look through the flowchart and determine White PPT T again.
“Complete What You Have Started!” – Sean
Sean
Master Trainer
Reply
T is Silver Chloride
It is one of the few insoluble chlorides out there.
The other one is Lead(II)Chloride, I think
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sean Reply:
December 15th, 2008 at 12:01 pm
Hi Raymond,
You are spot on.
For O Levels Chemistry Exams, the only chlorides that are insoluble are AgCl and PbCl2.
All the best
Sean
Master Trainer
Author
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1) P is lead(II) iodide, Q is calcium hydroxide, R is zinc chloride, T is silver chloride
2) R consists of Zn2+(the 2+ is a superscript) and Cl-(- is a superscript)
3) A is Calcium iodide and B is zinc
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sean Reply:
April 24th, 2009 at 2:13 pm
Hi “I love chemistry”,
I am glad you participated in the question.
Your answers are all correct. Keep up the good work.
PS: Look out for more questions in “O Levels Chemistry Tips Blog Marathon”.
To Your Academic Success in Chemistry,
Sean Chua
Master Trainer & Author
WINNERS Education Group
“Experience Learning with A Difference”
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oops and S is hydrogen gas
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sean Reply:
April 24th, 2009 at 2:13 pm
Hi,
Excellent!
Keep it up!
Sean Chua
Master Trainer & Author
WINNERS Education Group
“Experience Learning with A Difference”
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I thought nitrate ions are more reactive than chloride ions. Therefore, why is there a displacement reaction?
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Zyle Reply:
April 7th, 2010 at 9:19 pm
Zn is more reactive than Ag on the reactivity series.
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i don’t understand how you get calcium hydroxide for Q. And for anoym’s question, is it because of the metal displacement instead ?
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sean Reply:
May 6th, 2010 at 12:49 am
It is the Test for Cation Ca2+ using the reagent Sodium Hydroxide.
This is covered in Qualitative Analysis (QA).
Think about it.
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Can you put some videos on The Periodic Table, periodicity,organic chemistry and qualitative analysis? Thanks so much Sean. And, can you also help include some mole practises? Maybe more complex ones, rather than the easier ones. Thanks:)
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sean Reply:
May 6th, 2010 at 12:47 am
Check out the archive blogposts on the different topics.
Search are available on the rhs column.
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I don’t understand why is Q Ca(OH)2 because i thought it is an alkali and alkali are always soluble in water. So why is a precipitate then?
Definition of precipitate : An insoluble solid in a solution that is produced by a chemical reaction.
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i got all correct except R. where did the zinc come from??
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Hi. I am an NCEA lvl 2 chemistry student, and we are doing qualitative analisis at the moment. We have been asked to write out the ionic and complex equations that occur while finding the anion and cation PbNO3, in our chart there is no need to write any equations for NO3 as no precipitate is ever formed. However, one of the equations we must write for Pb2+ has stumped me, and I would be very glad if you could help.
I have done the first – add 2 drops of dilute NaOH solution. The resulting ionic equation was Pb2+ + OH- ^ Pb(OH)2.
Then – add excess NaOH solution, precipitate disappears. Pb2+ + 4OH- ^ (Pb(OH)4)2-.
But here is the issue. New sample, add two drops, then excess, NH3 solution. White precipitate forms. I need to write this equation, but how do you write –
Pb2+ + NH3 ^??????????
There is a precipitate so it needs to be an ionic equation. But NH3 has no chrge, it is impossible!
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Hi, What grade students do O level chemistry?
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can you please put the table of qualitative analysis for all metals,nonmetals,gases,solutions.
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