How many moles of sodium hydroxide can be added to 1L of a solution, 0.1M in NH3 and 0.1M in NH4Cl without changing the pOH by more than 2.00 unit? Assume no change in volume. Kb(NH3)=1.8×10−5.
A
0.0818
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B
0.818
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C
0.00818
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D
8.18
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Solution
The correct option is B0.0818 Initial pOH=pKb=4.744 Let x mole of NaOH has been added. [NH+]=0.1+x,[NH3]=0.1−x pOH=5.744 5.744=4.744+log0.1+x0.1−x 1=log0.1+x0.1−x 0.1+x0.1−x=10⇒x=0.911=0.0818 moles