This question is about Preparation of Salts that was sent to me by one of my Sec 4 Pure Chemistry student.
Before we take a look at the question, let’s recap that there are 3 main methods to prepare salts in the laboratory:
- Titration
- Acids + Excess Insoluble Substances
- Precipitation
If you need more information on Preparation of Salts, you can go to my earlier blogposts under archives.
Let’s take a look at the question.
Question:
A student was given two beakers, one containing an aqueous solution of sodium chloride and the other aqueous lead (II) nitrate. He was told to prepare lead (II) chloride using those reagents.
(i) What is the name of the method that he used to prepare the salt?
(ii) Name the other? product made, besides lead (II) chloride
(iii) Write an ionic equation for the preparation.
In the process of doing the experiment, he accidentally spilled some of the salt solutions. Since he could not obtain sufficient lead (II) chloride, he tried to prepare more lead (II) chloride by adding solid lead (II) carbonate to dilute hydrochloric acid. Effervescence was seen but the reaction stopped in a short while.
(iv) Why was there effervescence?
(v) Why was he unsuccessful in preparing lead (II) chloride from the process of adding dilute hydrochloric acid to lead (II) carbonate?
Go try it out and leave your answers (and workings) in the Comment Section below.
PS: Feel free to share this blogpost with your friends or classmates, if you think they will benefit from it
PPS: If you are new to this website, you can subscribe (right hand side) to receive more chemistry tips and questions
1.Neutralization
2.lead(¡¡)nitrite
I have a question , my question is Variation method for the free particle?
Salts are defined as products of acids plus metal,carbonates or base/alkai. Is salt produced when Group metals react with cold water?
Is water considered an acid?
What about displacement reactions? Do they produce salts since acid is not involved?
what is considered “salt” for O and A levels? thanks
(i) The method used to prepare lead (II) chloride is Precipitation Method.
(ii) The other product is sodium nitrate
(iii)Pb2+ (aq)+ 2 Cl-(aq) –> PbCl2(s)
(iv)When acid reacts with carbonate, carbon dioxide will form. Carbon dioxide is a gas, hence effervescence will be observed.
(v) A coating of lead (II) chloride will be formed at the outer layer of the lead (II) carbonate. The hard coating of lead (II) chloride prevents the lead (II) carbonate from reacting with the acid.
You are absolutely right! Good!
Lead (II) chloride, PbCl2 is an insoluble salt and thus forms a protective insoluble layer over the underlying lead (II) carbonate solid reactant.
🙂
I believe first 4 parts were quite clear cut so I would
skip that part.
v) It is because a layer of protection is formed around the lead(II) carbonate, hence preventing furthur reaction of the lead(II) carbonate with the acid.
hi, the answer for a is that when the two salt are soluble then only we can use preciptation method so precitation is not done. secondly i think we will use the method of titration.
Lead (II) chloride is an insoluble salt, so it can only be prepared using the precipitation method, and not titation.
srsly confused…could u explain?
dude. all nitrates are soluble. that means that lead (II) nitrate is soluble and sodium chloride is also soluble….so isnt the preparation method tritration?
1.precipitation 2.NaNO3 3.Pb2+ plus 2Cl- >>> PbCl2
4.carbondioxide was evolved 5.it failed since solid lead carbonate does not react with dilute acids
Hi Linda,
This question is solely on the topic of Organic Chemistry. However, the question is not very well set, as in the question is not specific enough.
Let me assume that you are following the GCE O-Level Syllabus, and then try to solve this question.
When an organic compound reacts with oxygen, i believe it meant combustion and the two products will be carbon dioxide (assuming sufficient amount of air available) and water vapour.
(a) X = Water Vapour. You can test it with anhydrous copper (II) sulfate powder. It will turn from white to blue colour in the presence of water.
(b) Y = Carbon Dioxide
(c) There is only one type of confirmatory test for unsaturation. Test with reddish-brown aqueous bromine solution. If compound is unsaturated, it will decolurise the aqueous bromine.
(d) Let us assume the organic compound to be a straight chain alkene. E.g. Ethene, C2H4
The chemical equation would be C2H4 + Br2 –> C2H4Br2
Above is an addition reaction, and is known as Bromination.
Note: Question ask for equation with structural formula, so you need to present it by drawing the 3 structures.
Hope this information helps. Let me know your thoughts on it.
For others, please give your views also. =)
hi ,i have question that i do not really know the right ans and explanation.pls help me,the question:
An organic compound reacts with oxygen to produce substances X and Y.(a)describe how you would confirm that X contains water .(b)name Y (c)describe how you would show that organic compound is unstaturated.
(d)using a suitable organic compound ,write an equation with structure formula to illustrate the ans to (c).
thank you.
Hi,
Hi,
You can do a keyword search for ?Preparation of Salts? on the top right-hand corner of this website.
From there you can find more discussions, notes and tips.
Rgds,
Sean Chua
Hi, please could you mail me a detailed explanation on salt preparation. It’d be very very helpful. P.s, i’m sitting for my O-levels in 5weeks! Thank a ton!
hi would to have a detailed explanation of the question on the preparing salt .not very sure of it.thx.
(v) alternatively, incomplete reaction (question is vague) could be due to PbCl2 produced initially at reaction forming a layer of coating on PbCO3 solid, preventing unreacted PbCO3 from reacting with HCl.
(i) precipitation
(ii) NaNO3
(iii) Pb2+(aq) + 2Cl- ( aq) —> PbCl2 (s)
(iv) HCl reacts with PbCO3 to form PbCl2, H2O and CO2; effervescence observed is CO2 produced in the reaction.
(v) PbCl2 and PbCO3 are both insoluble. By adding excessive amount of PbCO3 to HCl, residue obtained is a mixture of PbCl2 and PbCO3 rather than pure PbCl2.