Question

# Which of the following solutions will have pH equal to 1.0?  55 mL of M10 HCl + 45 mL of M10 NaOH  50 mL of M5 HCl + 50 mL of M5 NaOH  75 mL of M5 HCl + 25 mL of M5 NaOH  None of the above

Solution

## The correct option is C 75 mL of M5 HCl + 25 mL of M5 NaOH  We need to calculate the resulting molar concentration of H+ ions to determine the resulting pH of solutions. Here n-factor of NaOH and HCl is 1 . So Molarity and Normality are equal. Formula used is: Mmix=M1V1−M2V2V1+V2    if M1V1>M2V2 Option A: (0.1×55)>(0.1×45) Nmix=(0.1×55)−(0.1×45)100=0.01pH=−log(0.01)=2×log(10)=2 Option B: Since the concentration and volume of both  NaOH and HCl is equal. It forms a neutral solution of pH=7 Option C: (0.2×75)>(0.2×25) Nmix=(0.2×75)−(0.2×25)100=0.1pH=−log(0.1)=log(10)=1

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