4. Magnesium

1. Potassium hydroxide

$Mg^{2+}$ $+$ $2OH^-$ $\longrightarrow$ $Mg(OH)_2$ - white gelatinous precipitate - soluble in dilute mineral acids

2. Ammonia

$Mg^{2+}$ $+$ $2OH^-$ $\longrightarrow$ $Mg(OH)_2$ - Precipitation less complete than with $KOH$ - The presence of $NH_4Cl$ in sufficient qty inhibits precipitation

3. Ammonium carbonate

$Mg^{2+}$ $+$ $CO_3^{2-}$ $\longrightarrow$ $MgCO_3$ - White crystalline precipitate - Soluble in dilute mineral acids - The presence of $NH_4Cl$ in sufficient qty inhibits this precipitation, and that allows to precipitate the alkaline earth carbonates excluding $MgCO_3$

4. Sodium hydrogenophsphate in the presence of $NH_3$/$NH_4Cl$

$Mg^{2+}$ $+$ $NH_3$ $+HPO_4^{2-}$ $\longrightarrow$ $MgNH_4PO_4$ - White crystalline precipitate - soluble in HCl $ $ - soluble in acetic acid - Possibly rub

5. Magneson II (p-nitrobenzene-azo-α-naphtol)

- In the presence of $Mg^{2 +}$, the strongly alkaline solution of reagent turns red-purple to azure blue.

5. Thiazole yellow

- In the presence of $Mg^{2+}$, the strongly alkaline solution of reagent turns from yellow-orange to flame-red .