Question

Please help me make analysis scheme flow chart for the detection of cation present in my unknown salt mixture of Ag+, Pb2+, or Ca2+ cations based on their solubility in the given reagents.

I can only use these reagents: Na2CO3, NaCl, & Na2SO4

The suspected cations in the unknown cation mixture are: Ag+, Pb2+, or Ca2+.

I used 0.5 M solution of all these reagents.

My test results are:

Na2CO3: 20 drops of sodium carbonate were used and silver blue precipitate was produced.

NaCl: 20 drops of sodium chloride were used and no precipitate was formed.

Na2SO4: 20 drops of sodium sulfate were used yellow precipitate was produced.

Please please help me make analysis flow chart based on this information and also tell me in what sequence these reagents will be added to unknown salt mixture.

I suspect that the cation may be Ca2+ based on solubility rules. But I'm not sure.

Answer 1

The possible action your solution might contain is amongst $Ag^+$, $Pb^{2+}$, or $Ca^{2+}$.

What are the solutions?

A solution is a homogeneous mixture of one or more solutes dissolved in a solvent.

NaCl: 20 drops of NaCl were used and no precipitate was formed.

No precipitation formed means the $Cl^-$ cation is soluble in water. From your chart, you might see the halide of $Ag^+$ and $Pb^{2+}$ is insoluble in water, which means they should have formed precipitation but you didn't. This means there's less possibility it contains $Ag^+$ or $Pb^{2+}$, so we are left with only $Ca^{2+}$. Let's confirm it with the rest.

$Na_2SO_4$ : 20 drops of $Na_2SO_4$ were used yellow precipitate was produced.

Even though all other sulfates form precipitation ( Insoluble in water)

$Na_2CO_3$ : 20 drops of sodium carbonate were used and the silver-blue precipitate was produced.

It seems all of their Carbonate is insoluble in nature. ( which is our case too ).

From the above result, only the reaction with NaCl was deemed to be decisive and it indeed contains $Ca^{2+}$ ions. Means you are correct.

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