suppose you have a solution that might contain any or all of the following catio

Question

suppose you have a solution that might contain any or all of the following cations: Cu2+, Ag+, Ba2+, and Mn2+. the addition of HBr causes a precipitate to form. After the precipitate is filtered off, H2SO4 is added to the supernate, and another precipitate forms. This precipitate is filtered off, and a solution of NaOH is added to the supernatant liquid until it is strongly alkaline. No precipitate is formed. Which ions are present in each of the precipitates? which cations are not present in the original solution?

Explanation / Answer

First step:

addition of HBr will add H+ and Br-,

Note that that:

Ag+(aq) + Br-(aq) --> AgBr(s) forms

AgBr is likely to precipitate if enough Br- is added.... therefore this precipitate is AgBr.

Step 2:

Then, after filtration, H2SO4 addition will form most likely

Ba2+(aq) + SO4-2(aQ) = BaSO4(s)

If there is enough SO4-2 in solution, expect BaSO4 to form

After Filtration...

Step 3)

NaOH is added, but no precipitate forms

This implies that no Mn+2 and Cu+2 are present... since those should form Mn(OH)2 and Cu(OH)2 respectively...

therefore, they are not present

only ions = Ag+, Ba+2

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