NEET Practice Questions (MCQs) with Answers & Solutions

When a solution containing oxalate ions is added to a mixture of $Ba^{2+}$, $Sr^{2+}$, and $Ca^{2+}$, all three cations will precipitate out as their respective oxalates: $BaC_2O_4$, $SrC_2O_4$, and $CaC_2O_4$.

The ion that cannot be precipitated by both HCl and $H_2S$ is $Cu^{2+}$. Copper(II) ions can be precipitated by $H_2S$ but not by HCl. This is because $HCl$ does not form an insoluble compound with $Cu^{2+}$ ions, whereas $H_2S$ forms an insoluble copper(II) sulfide ($CuS$) precipitate.

$Pb(CH_3COO)_2$ (lead acetate) reacts with $H_2S$ (hydrogen sulfide) to form a black precipitate of lead sulfide ($PbS$). This is a common qualitative analysis reaction used to test for the presence of lead ions.

The $Fe^{2+}$ ion can be distinguished from the $Fe^{3+}$ ion using $NH_4SCN$ (ammonium thiocyanate). When $NH_4SCN$ is added to a solution containing $Fe^{3+}$ ions, it forms a blood-red complex, while $Fe^{2+}$ ions do not react in the same way. This is a common qualitative test to differentiate between these oxidation states of iron.

The addition of $K_4[Fe(CN)_6]$ (potassium ferrocyanide) to an aqueous solution of $FeCl_3$ (ferric chloride) results in a color change. A deep blue color, known as Prussian blue, is formed due to the formation of $Fe_4[Fe(CN)_6]_3$. This reaction is a well-known test for the presence of $Fe^{3+}$ ions.

Chromic acid is formed by mixing potassium dichromate ($K_2Cr_2O_7$) with concentrated sulfuric acid (conc. $H_2SO_4$). The reaction produces $H_2CrO_4$ (chromic acid) and is used in various oxidation reactions in organic and inorganic chemistry.

The solubility of ionic compounds in water depends on the lattice energy and the hydration energy. MgS has a higher lattice energy due to the highly charged ions $Mg^{2+}$ and $S^{2-}$, which makes it less soluble in water compared to the other options listed.

Lead sulphate is soluble in concentrated nitric acid because the nitric acid reacts with the lead sulphate to form soluble lead nitrate. The reaction involves the dissolution of $PbSO_4$ in $HNO_3$ forming $Pb(NO_3)_2$ and sulfuric acid, which are soluble in water.

When $H_2S$ gas is passed through HCl containing aqueous solutions of $CuCl_2, HgCl_2, BiCl_3,$ and $CoCl_2$, all form insoluble sulfides except $Co^{2+}$. $CoS$ does not precipitate out due to its higher solubility product (Ksp) compared to the other metal sulfides.