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2

The ion $\ce{CO3^{2-}}$ introduced in the first reaction must be produced by dissolving a soluble carbonate like $\ce{Na2CO3}$. On the other hand $\ce{BaCl2}$ or $\ce{CaCl2}$ have to be dissolved in water to react. If they are introduced as solid these substances will not react, unless they slowly get dissolved. Nobody really knows why these chlorides are ...

1

On writing the equations for the initial precipitation and the dissolution reactions, it can be seen that their equilibrium constants are not the same. Taking $K_1,K_2$, and $K_3$ to be the constants for each of these and the double dissociation of $\ce{H2CO3}$ respectively, you get $$K_2=\frac{1}{K_1K_3} \neq K_1$$ This is why you can't reason out that the ...

4

First iron(II) hydroxide $\ce{Fe(OH)2}$ is a precipitate made in aqueous solution, and it does not react with ammonia. Second, the iron(II) hydroxide $\ce{Fe(OH)2}$ is a green substance which is extremely sensitive to the oxygen of the air. In a couple of minutes, it gets brown, due to the formation of iron(III) hydroxide $\ce{Fe(OH)3}$ according to \ce{4 ...

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