CET Karnataka Medical CET - Karnataka Medical Solved Paper-2010

  • question_answer
    \[0.023g\]of sodium metal is reacted with \[100c{{m}^{3}}\]of water. The pH of the resulting solution is

    A)  \[10\]              

    B)  \[11\]

    C)  \[9\]               

    D)  \[12\]

    Correct Answer: D

    Solution :

    \[\underset{2mol}{\mathop{2Na}}\,+\underset{2mol}{\mathop{2{{H}_{2}}O}}\,\xrightarrow{{}}\underset{2mol}{\mathop{2NaOH}}\,+{{H}_{2}}\] Given, \[\frac{0.023}{23}mol\frac{100}{22400}mol\] \[=1\times {{10}^{-3}}mol\] \[=4.46\times {{10}^{-3}}mol\] Thus, \[Na\] is the limiting reagent and decide the amount of \[NaOH\] formed. \[\because \] 1 mole Na give \[NaOH=1\text{ }mol\] \[\therefore \] \[1\times {{10}^{-3}}\] mole Na will give \[NaOH\] \[=1\times {{10}^{-3}}mol\] Concentration of \[[O{{H}^{-}}]=\frac{1\times {{10}^{-3}}\times 1000}{100}=1\times {{10}^{-2}}\] \[pOH=-\log [O{{H}^{-}}]\] \[=-\log (1\times {{10}^{-2}})\] \[=2\] \[pH=14-2=12\]


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