Which of the following mixture solution has `pH ~~ 1.0`?

Options

A. `100 mL M//10 HCI + 100 mL M//10 NaOH`
B. `55 mL M//10 HCI +45 mL M//10 NaOH`
C. `10 mL M//10 HCI + 90 mL M//10 NaOH`
D. `75 mL M//5 HCI +25 mL M//5 NaOH`

Answer

D

Explanation

a. `HCI = 100 xx (1)/(10) = 10 mEq`
`NaOH = 100 xx (1)/(10 = 10 mEq`
Salt of `S_(A)//S_(B)` is formed, `pH = 7`
b. `HCI = 55 xx (1)/(10) = 5.5 mEq`
`NaOH = 45 xx (1)/(10) = 4.5 mEq`
`1.0 mEq` of `HCI` is left. So `pH` will be in acidic range but not equal to one, since concentration fo `HCI` is very low.
c. `HCI =10 xx (1)/(10) = 1mEq`
`NaOH = 90 xx (1)/(10) =9 mEq`
`8 mEq of NaOH` is left and `pH gt 7`.
d. `HCI = 75 xx (1)/(5) = 15 mEq`
`NaOH = 25 xx (1)/(5) = 5 mEq`
`15 - 5 = 10 mEq of HCI` is left.
`:. [HCI] = [H_(3)O^(o+)] = (10 mEq)/((75+25)mL) = (10)/(100) = 0.1M`
`pH =- log (10^(-1)) = 1`.