Question

1.The first thing needed was to add 3 drops of HCl to precipitate the ions out as chlorides
of Ag 2+ , Hg 2+, and Pb 2+ . Do you think that 3 drops of HCl will be enough to precipitate all of these three ions? If not, what would you do to check?

2. If you didn’t get any precipitation with the addition of the HCl, which would you conclude? (choose one of the following)

   a. You do not have any silver or mercury ions but you might have lead ions present.(explain below if you choose this answer)

   b. You don’t have any Group I ions

   2. You didn’t add enough HCl

3. You found that you had a precipitate the first time you added the HCl.

a. What does it mean if you have no further precipitate the second time you add HCl to the solution separated from the white precipitate from the lab.

b. If you get a precipitate this second time, do you think you have all of the precipitate now? Explain your answer.

Answer 1

1. Getting a precipitate by adding 3 drops is a vague term as we have to define how much quantity of the salt we have.Also what is the concentration of HCl used.However,even if two drops of HCl(6M) is used for detection of these salts,all salts will be precipitated in the form of there chlorides.So It is possible that all the salt present in the solution may not get precipitated with the addition of 3 drops of HCl which depends on the HCl concentration.It can be checked by further addition of HCL.If more amount of salt gets precipitated,that means they were not precipitated earlier fully.

But if I didn't get any precipitate after adding 3 drops of HCl,I will conclude that (b) Group I cations are absent from the given sample of salt.This is because whenever we need to detect any salt ,the first thing is that we check what is the group number of salt and then the preliminary test is done for those salts so as to get an estimate that this salt might be present after doing preliminary test and then we proceed for further confirmatory test.So giving precipitate on the addition of dilute HCl is the preliminary test for Group I cations.

3.(a) When no precipitate is formed after the further addition of HCl to the solution centrifuged from precipitated one,that means we have already separated Group I cations from the solution and they are in the form of there precipitate.Also we may have presence of other group Cations in the solution,that is to be checked by further preliminary test.

(b) If we get the precipitate second time as well,then it can be concluded that Group I cations were not fully separated earlier.However,we also cann't make sure that all the cation of group I are precipitated as it gain depends on the quantities of HCl we add and their concentration.But if this HCl would have been added in sufficient quantities then we can be sure of that we have separated all group I cations.