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KVPY Sample Paper KVPY Stream-SX Model Paper-10

  • question_answer
    The sodium salt of a carboxylic acid, was Produced by passing \[{{\operatorname{CO}}_{2}}\]into an aqueous Solution of caustic alkali at an elevated Temperature and pressure. On heating in presence of sodium hydroxide followed by Treatment with sulphuric acid gave a dibasic acid, C. A sample of \[0.4\]g of acid C, on combustion Gave \[0.08\]g of water and \[0.39\]g of carbon dioxide. The silver salt of the acid C weighing \[1.0\]g on ignition yielded 0.71 g of silver as residue. Identify C.

    A) \[\operatorname{HCOOH}\]                   

    B) \[{{(COOH)}_{2}}\]

    C) \[{{\operatorname{CH}}_{3}}COOH\]               

    D) \[{{\operatorname{NH}}_{3}}\]

    Correct Answer: B

    Solution :

    the given set of reactions can be represented
    as below:\[\operatorname{Aq}.NaOH\xrightarrow[High\,\,tem.,]{Gas\,B}Sod.\,salt\,of\,acid\,A\]            \[\xrightarrow[(ii){{H}_{2}}S{{O}_{4}}]{(i)NaOH(heat)}Dibasic\,Acid,\,C\]
    Calculation of molecular formula of C
    \[%\operatorname{of}\,H=\frac{2}{18}\times \frac{0.08}{0.40}\times 100=2.22%\]\[%\operatorname{of}\,C=\frac{12}{44}\times \frac{0.39}{0.40}\times 100=27.30%\]\[%\operatorname{of}\,O=100-\left( 2.22+27.30 \right)=71.48%\]
    By usual method, empirical formula of acid C is \[{{\operatorname{CHO}}_{2}}\]
    \[\operatorname{Eq}.wt\,of\,acid\,C=\left( \frac{1.0}{0.71}\times 108 \right)-107=45\]
    Mol. Wt. of acid \[C=45\times 2=90\]
    \[\therefore \]Mol. formula of \[C={{C}_{2}}{{H}_{2}}{{O}_{4}}\]
    Since it is dicarboxylic and it must have two
    \[-COOH\,groups\,hence\,C\,is\,\,\underset{\underset{Oxilic\,acid}{\mathop COOH}\,}{\mathop{\overset{\underset{{}}{\mathop COOH}\,}{\mathop{|}}\,}}\,\,\]
    Complete series of reaction will be,\[2NaOH\left( aq. \right)\xrightarrow{2C{{O}_{2}}\left( B \right)}\underset{\underset{{}}{\mathop HCOONa}\,}{\mathop{\overset{\overset{{}}{\mathop HCOONa}\,}{\mathop{+}}\,}}\,\]
    \[\xrightarrow[heat]{NaOH}\underset{\underset{{}}{\mathop COONa}\,}{\mathop{\overset{\overset{{}}{\mathop COONa}\,}{\mathop{|}}\,}}\,\xrightarrow{{{H}_{2}}S{{O}_{4}}}\underset{\underset{(C)}{\mathop COONa}\,}{\mathop{\overset{\overset{{}}{\mathop COONa}\,}{\mathop{|}}\,}}\,\]


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