So, I am supposed to pretend to be an expert and decide if someone was guilty of

Question

So,

I am supposed to pretend to be an expert and decide if someone was guilty of not finding lead in the water system. I am given this statement and supposed to deternine if its good evidence or not. In as much detail as possible please tell me if its good or bad information and why? A water sample taken evaporated over the weekend, after filtering TDS (total dissolved solids) reading 0.462 g (limit 500 mg). Solids dissolved in 50 mL 6.0 MHNO3, Add 8.0 M NaOH carefully (exothermic) until basic. CLoudy precipitate is observed

Explanation / Answer

Lead (Pb) in its dichlorride salt (PbCl2) or sulphate (PbSO4) form doesnot dissolve in water or even HCl and H2SO4.

On treatment with 6.0M HNO3 (nitric acid), HNO3 oxidizes Pb to Pb(NO3)2 which dissolves in aqueous phase.

Then on treatment with strong, concentrated base like NaOH, Pb(NO3) will form a white water insoluble ppt of Pb(OH)2 and solution appears cloudy,

Pb(NO3)2 + 2NaOH ----------> Pb(OH)2 + 2NaNO3

White solid water insoluble (Under basic conditions)

Hence an evidence for Pb presence.

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