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KVPY Sample Paper KVPY Stream-SX Model Paper-9

  • question_answer
                             A 0.60 g sample consisting of only \[Ca{{C}_{2}}{{O}_{4}}\]and \[Mg{{C}_{2}}{{O}_{4}}\] is heated at \[500{}^\circ C,\]converting the two salts of \[CaC{{O}_{3}}\] and \[MgC{{O}_{3}}.\] The sample then weighs 0.465 g. If the sample had been heated to \[900{}^\circ C,\]where the products are \[CaO\] and \[MgO,\]what would the mixtures of oxides have weighed?

    A) 0.12 g              

    B) 0.21 g

    C) 0.252 g

    D) 0.3 g

    Correct Answer: C

    Solution :

    Let x gm\[Ca{{C}_{24}}\]
    \[Ca{{C}_{2}}{{O}_{4}}\xrightarrow{\Delta }CaC{{O}_{3}}\xrightarrow{\Delta }CaO\]
    \[\begin{matrix}    \frac{x}{128}mole & \frac{x}{128}mole & \frac{x}{128}mole  \\ \end{matrix}\]
    Let \[0.6-x\,\,gm\,\,Mg{{C}_{2}}{{O}_{4}}\]
    \[Mg{{C}_{2}}{{O}_{4}}\xrightarrow{\Delta }MgC{{O}_{3}}\xrightarrow{\Delta }MgO\]
    \[\begin{matrix}    \frac{0.6-x}{112}mole & \frac{0.6-x}{112}mole & \frac{0.6-x}{112}mole  \\ \end{matrix}\]
    [A]
    Weight of \[CaO+MgO\]
    \[=\frac{0.48}{128}\,\,\times \,\,56+\frac{0.12}{112}\,\,\times \,\,40=0.252\,\,gm\]


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