MCQ
The Lassaigne’s extract is boiled with dil. $HNO_3$ before testing for halogens because
- ASilver halides are soluble in $HNO_3$
- ✓$Na_2S$ and $NaCN$ are decomposed by $HNO_3$
- C$Ag_2S$ is soluble in $HNO_3$
- D$AgCN$ is soluble in $HNO_3$
$N{a_2}S + 2AgN{O_3} \to 2NaN{O_3} + \mathop {A{g_2}S}\limits_{Black} \downarrow $
$NaCN + AgN{O_3} \to NaN{O_3} + \mathop {AgCN}\limits_{White} \downarrow $
$NaCl + AgN{O_3} \to NaN{O_3} + \mathop {AgCl}\limits_{white} \downarrow $
$N{a_2}S + 2HN{O_3}\xrightarrow{{boil}}2NaN{O_3} + {H_2}S \uparrow $
$NaCN + HN{O_3}\xrightarrow{{boil}}NaN{O_3} + HCN \uparrow $
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| List$-I$ | List$-II$ |
| $(A)$ Spontaneous process | $(I)\,\Delta H < 0$ |
| $(B)$ Process with $\Delta P =0 \;\Delta T =0$ | $(II)\,\Delta G _{ T , P } < 0$ |
| $(C)\,\Delta H _{reaction}$ | $(III)$ Isothermal and isobaric process |
| $(D)$ Exothermic process | $(IV)$ [Bond energies of molecules in reactants] - [Bond energies of product molecules] |
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