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  4. 50 mL of 0.1 M HCl and 50 mL of 0.2 M NaOH are mixed. The pH of the resulting solution is

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Q. 50 mL of 0.1 M $ HCl $ and 50 mL of 0.2 M NaOH are mixed. The pH of the resulting solution is

CMC MedicalCMC Medical 2012

Solution:

$ 50\,\,mL $ of $ 0.1\,M\,HCl=\frac{0.1\times 50}{1000}=5\times {{10}^{-3}} $ $ 50\,\,mL $ of $ 0.2\,M\,NaOH=\frac{0.2\times 50}{1000}=10\times {{10}^{-3}} $ Hence, after neutralisation NaOH left. $ =10\times {{10}^{-3}}-5\times {{10}^{-3}} $ $ =5\times {{10}^{-3}} $ Total volume = 100 cc The concentration of NaOH $ =\frac{5\times {{10}^{-3}}\times 1000}{100}=0.05\,M $ $ [O{{H}^{-}}]=0.05\,M=5\times {{10}^{-2}}\,M $ $ pOH=-\,\log \,[O{{H}^{-}}] $ $ =-\,\log \,[5\times {{10}^{-2}}] $ $ =1.3010 $ $ pH+pOH=14 $ $ pH=14-1.3010 $ $ =12.699=12.70 $