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Is it necessary to acidify a solution be...

Is it necessary to acidify a solution before group II cations are precipitated with `H_(2)S`?

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Yes, because for the precipitation of cations of group II only small concentration of sulphide ions `(S^(2-))` is required this condition is achieved by passing `H_(2)S` gas in a solution acidified with `HCl` (dil.) due to common ion effect concentration of `S^(2-)` ions decreases as presence of hydrochloric acid suppresses the ionisation of `H_(2)S` resulting only in the precipitation of sulphides of group II metals.
Other metal sulphides remain in solution as they required higher concentration of `S^(2-)` ions for their precipitation.
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Which of the following cations form(s) black precipitate(s) with H_(2)S (g) ?

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In equalitative analysis, cations of graph II as well as group IV both are precipitated in the form of sulphides. Due to low value of K_(sp) of group II sulphides, group reagent is H_(2)S in the presence of dil. HC1 , and due to high value of K_(sp) of group IV sulphides, group reagent is H_(2)S in the presence of NH_(4)OH and NH_(4)C1 . In a solution containing 0.1M each of Sn^(2+), Cd^(2+) , and Ni^(2+) ions, H_(2)S gas is passed. K_(sp) of SnS = 8 xx 10^(-29), K_(sp) of CdS = 15 10^(-28), K_(sp) of NiS - 3 xx 10^(-21), K_(1) of H_(2)S = 1 xx 10^(-7), K_(2) of H_(2)S = 1 xx 10^(-14) At what value of pH, NiS will start to precipitate?

In equalitative analysis, cations of graph II as well as group IV both are precipitated in the form of sulphides. Due to low value of K_(sp) of group II sulphides, group reagent is H_(2)S in the presence of dil. HC1 , and due to high value of K_(sp) of group IV sulphides, group reagent is H_(2)S in the presence of NH_(4)OH and NH_(4)C1 . In a solution containing 0.1M each of Sn^(2+), Cd^(2+) , and Ni^(2+) ions, H_(2)S gas is passed. K_(sp) of SnS = 8 xx 10^(-29), K_(sp) of CdS = 15 10^(-28), K_(sp) of NiS - 3 xx 10^(-21), K_(1) of H_(2)S = 1 xx 10^(-7), K_(2) of H_(2)S = 1 xx 10^(-14) Which of the following sulphides is more soluble in pure water?

CENGAGE CHEMISTRY-QUALITATIVE INORGANIC SALT ANALYSIS-Viva Voce Questions And Part-C (Analysis Of Cations)
  1. Why are only Pb^(2+),Ag^(o+) and Hg(2)^(2+) ions precipitated in group...

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  2. Why is lead plaed in gourp I as well in II?

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  3. Is it necessary to acidify a solution before group II cations are prec...

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  4. Give the reason for the formation of a light yellow or white ppt. in t...

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  5. Why do we Prefer HCl for preparing solution of cations?

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  6. Is it advisable to use conc. HCI in place of dilute HCI for preparing ...

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  7. Why is it essential to boil off H(2)S gas before proceeding to group I...

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  8. Can the solution be acidified with HNO(3) in group II before passing H...

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  9. What can it be, if the precipitate of group I is soluble in hot water ...

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  10. Why is H(2)SO(4) never employed for preparing original solution for th...

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  11. Group I filtrate is made moderately acidic before proceeding to group ...

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  12. What is the

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  13. Why do we add excess of NH(4)Cl and NH(4)OH in the precipitation of gr...

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  14. Why is it essential to oxidise ferrous salt to ferric salt in group II...

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  15. Can NH(4)Cl be replaced by any other ammonium salt for the precipitati...

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  16. How will you distinguish between ferrous and ferric salts?

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  17. Can we add NH(4)OH first and NH(4)Cl later in the analysis of group II...

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  18. Can we use NaCla and NaOH in place of Na(4)Cl and NH(4)OH in the group...

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  19. Why are Zn,MnNi,Co not precipitated n the group III as hydroxides?

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  20. Why are the group IV cations not precipitated as sulphides on passing ...

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