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KVPY Sample Paper KVPY Stream-SX Model Paper-10

  • question_answer
    \[100mL\]of tap water containing \[\operatorname{Ca}{{\left( HC{{O}_{3}} \right)}_{2}}\] Titrated with \[\operatorname{N}/50 HCl\] with methyl orange as Indicator. If \[30 mLof\,HCl\] were required, calculate the temporary hardness as parts of \[{{\operatorname{CaCO}}_{3}}\]per \[{{10}^{6}}\]Parts of water.

    A) \[150ppm\]                    

    B) \[300 ppm\]

    C) \[450 ppm\]                   

    D) \[600 ppm\]

    Correct Answer: B

    Solution :

    \[\operatorname{Milliequivalent}\]of \[\operatorname{Ca}{{\left( HC{{O}_{3}} \right)}_{2}}\] 
    \[\equiv  Milliequivalent of\]\[{{\operatorname{CaCO}}_{3}}\]
    \[\equiv  Milliequivalent of\,HCl\]
    Now,     \[{{\operatorname{V}}_{1}}{{N}_{1}}={{V}_{2}}{{N}_{2}}\]\[1000\times \frac{\operatorname{w}}{100/2}=30\times \frac{1}{50}\Rightarrow \operatorname{w}=0.03g\]
    For 100mL the amount of \[{{\operatorname{CaCO}}_{3}}\]\[=0.03g=0.03g\times 1{{0}^{3}}\]
    For \[{{10}^{6}}\operatorname{mL}=\frac{0.03}{100}\times {{10}^{6}}=300\operatorname{ppm}\]


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