A sample consists of one or more of the following salts: NH4NO3, Na2SO4, NaNO3,

Question

A sample consists of one or more of the following salts: NH4NO3, Na2SO4, NaNO3, Li2S, Ca(NO3)2. The sample dissolves completely in water, and the solution is divided into three parts. Adding AgNO3 solution to one part gives a black precipitate. Heating the second part with NaOH produces a gas which turned moist red litmus paper blue, and smelled of NH3. The third part gives a white precipitate when mixed with Na2SO4 solution.

Which compounds MUST be present? Explain why. (Write the formulae and present your evidence.)

Which compounds MUST be absent? (Explain why. Write the formulae and present your evidence.)

Which compounds are INDETERMINATE (unable to determine if present or absent. Write the formulae.)

Explanation / Answer

NH4NO3, Na2SO4, NaNO3, Li2S, Ca(NO3)2

addition og AgNO3, gives a black precipitate

From the list, only

Ag2SO4 and Ag2S can be formed, which have white and black color respetively

therefore, Li2S must be present

b)

heating with NaOH produces a has... and smells like NH3 = must be NH3(G)

The only way to produce this is via

NH4NO3 presence

NH4NO3 + OH- --> NH3(g) + H2O(l) + NO3-(aq)

c)

when addition of Na2SO4, there is white precipitate

Which compounds MUST be present? Explain why. (Write the formulae and present your evidence.)

this must be NH4NO3 AND Li2S

Which compounds MUST be absent? (Explain why. Write the formulae and present your evidence.)

NONE

Which compounds are INDETERMINATE (unable to determine if present or absent. Write the formulae.)

Na2SO4 and NaNO3 can't be identified via previous procedures

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