A white solid is known to consist of one or more of the following compounds: AgN
ID: 475659 • Letter: A
Question
A white solid is known to consist of one or more of the following compounds: AgNO_3, Na_2CO_3, CaCl_2, and Pb(NO_3)_2 A sample of the solid is treated in the following manner: When cold water is added and the mixture is stirred, a white precipitate formed in the solution which remains even after the solution is boiled. The solution is centrifuged and decanted. The precipitate is separated into two parts, which are then treated as follows: When cold 3M HNO_3 is added to one part until the solution is acidic, the precipitate dissolves completely. When hot 3M HCl is added to the second part until the solution is acidic, the precipitate remains, even after heating to boiling. For each solid, indicate whether these results indicate the presence or absence from the sample.Explanation / Answer
A white solid is known to consist of one or more of the following compounds: AgNO3 , Na2CO3, CaCl2, and Pb(NO3)2. A sample of the solid is treated in the following manner: When cold water is added and the mixture is stirred, a white precipitate formed in the solution which remains even after the solution is boiled. The solution is centerifuged and decanted. The precipitate is separated into two parts, which are then treated as follows: When cold 3M HNO3 is added to one part until the solution is acidic, the precipitate remains, even after heating to boiling. For each solid, indicate wheter these results indicate the presence or absence from the sample.
Na2CO3 ---> absence, because in water, the sodium will form soluble NaOH, and the CO3 will form H2CO3, which decomposes to CO2 and H2O, and would bubble. No precipitate would form from this solid.
The Ag in AgNO3 will form a white solid, AgOH. This AgOH will dissolve in HNO3 though, so this compound is not present.
CaCl2 will dissolve in water completely, so it is not present in the precipitate.
Pb(NO2)2 will form a white precipitate, Pb(OH)2 in water. It will then not be dissolved by the HNO3 either. It is present in the sample.
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