`1)n_[H^+]=0,02.0,1=0,002(mol)`

`n_[OH^-]=0,01.0,3=0,003(mol)`

 `=>[H^+]=[0,002]/[0,1+0,3]=5.10^[-3](M)`

 `=>pH=-log(5.10^[-3])=2,3`

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`2)n_[H^+]=0,01.0,5=0,005(mol)`

    `n_[OH^-]=0,02.0,5=0,01(mol)`

`=>[H^+]=[0,005]/[0,5+0,5]=5.10^[-3](M)`

 `=>pH=-log(5.10^[-3])=2,3`

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`3)n_[H^+]=0,001.0,2=0,0002(mol)`

    `n_[OH^-]=0,002.0,3=0,0006(mol)`

 `=>[H^+]=[0,0002]/[0,2+0,3]=4.10^[-4](M)`

 `=>pH=-log(4.10^[-4])=3,4`

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`4)n_[H^+]=0,5.0,5=0,25(mol)`

    `n_[OH^-]=0,25.2.0,5=0,25(mol)`

  `=>[H^+]=[0,25]/[0,5+0,5]=0,25(M)`

  `=>pH=-log(0,25)=0,6`