Question

consider the following salts: pb(no3)2; (nh4)2so4; cuco3 and nahco3. which of the salts(s) would: (i) not dissolve readily in cold water; (ii) turn(s) black when heated strongly; (iii) produce(s) effervescence with dil. hcl; (iv) give(s) off a gas on warming with naoh; (v) produce(s) a yellow precipitate when ki (aq) is added to a solution of the salt.

Explanation:

Step1: Analyze solubility of salts

Solubility rules help here. $Pb(NO_3)_2$ is soluble in cold - water as most nitrates are soluble. $(NH_4)_2SO_4$ is also soluble in cold - water as ammonium salts and sulfates (except with some cations like $Ba^{2 + }$) are soluble. $CuCO_3$ is insoluble in water. $NaHCO_3$ is soluble in water. So the salt that does not dissolve readily in cold - water is $CuCO_3$.

Step2: Analyze reaction with HCl

$CuCO_3$ reacts with dil. HCl to produce effervescence due to the formation of $CO_2$ gas: $CuCO_3 + 2HCl=CuCl_2 + H_2O+CO_2\uparrow$.

Step3: Analyze reaction on heating

$CuCO_3$ decomposes on heating to form black $CuO$: $CuCO_3\xrightarrow{\Delta}CuO + CO_2\uparrow$.

Step4: Analyze reaction with KI

$Pb(NO_3)_2$ reacts with KI to give a yellow precipitate of $PbI_2$: $Pb(NO_3)_2 + 2KI = PbI_2\downarrow+2KNO_3$.

Answer:

(i) $CuCO_3$; (ii) $CuCO_3$; (iii) $CuCO_3$; (iv) $Pb(NO_3)_2$; (v) $Pb(NO_3)_2$