CET Karnataka Medical CET - Karnataka Medical Solved Paper-2010

  • question_answer
    A white crystalline salt A reacts with dilute \[HCl\] to liberate a suffocating gas B and also forms a yellow precipitate. The gas B turns potassium dichromate acidified with dilute \[{{H}_{2}}S{{O}_{4}}\] to a green coloured solution C. A, B and C are respectively

    A)  \[N{{a}_{2}}S{{O}_{3}},S{{O}_{2}},\,C{{r}_{2}}{{(S{{O}_{4}})}_{3}}\]

    B)  \[N{{a}_{2}}{{S}_{2}}{{O}_{3}},S{{O}_{2}},C{{r}_{2}}{{(S{{O}_{4}})}_{3}}\]

    C)  \[N{{a}_{2}}S,S{{O}_{2}},C{{r}_{2}}{{(S{{O}_{4}})}_{3}}\]

    D)  \[N{{a}_{2}}S{{O}_{4}},S{{O}_{2}},C{{r}_{2}}{{(S{{O}_{4}})}_{3}}\]

    Correct Answer: B

    Solution :

    Gas B turns the colour of acidified \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\] green thus it is \[S{{O}_{2}}\] and \[S{{O}_{2}}\] is obtained along with yellow precipitate when thio sulphate is treated with dilute acids. Thus, A is \[N{{a}_{2}}{{S}_{2}}{{O}_{3}},\]B is \[S{{O}_{2}}\] and C is \[C{{r}_{2}}{{(S{{O}_{4}})}_{3}}\]. The reactions are as follows \[N{{a}_{2}}{{S}_{2}}{{O}_{3}}+HCl\xrightarrow{{}}\underset{\begin{smallmatrix}  suffocating\,gas \\  (B) \end{smallmatrix}}{\mathop{S{{O}_{2}}}}\,\] \[+NaCl+{{H}_{2}}O+\underset{yellow}{\mathop{S}}\,\] \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}+S{{O}_{2}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{{}}{{K}_{2}}S{{O}_{4}}\]                \[+C{{r}_{2}}\underset{green}{\mathop{{{(S{{O}_{4}})}_{3}}+{{H}_{2}}O}}\,\]


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