Through a solution containing Cu2+ and Ni2+, H2S gas is passed after adding dil HCl. Which will precipitate out and why?
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Solution
When H2S gas is passed after adding dilute HCl due to common ion effect the ionization of H2S gas is decreased.
KSP value of copper sulphide is less than nickel sulphide because precipitation of copper sulphide requires low concentration of sulphide which is decreased by adding HCl hence Ni+2 gets precipitated.