Which of the following mixture/solution will show pH approximately equal to 9 ?

Options

A. `100 mL` of `3xx10^(-3)M HCI+100mL` of `4.24xx10^(-3)M NaCN`
B. `100 mL` of `0.01M NH_(4)OH+100 mL` of `2xx10^(-3)M NaOH`
C. `0.2M` sodium butyrate, `K_(a)` for butyric acid is `2.0xx10^(-5)`
D. `5xx10^(-6)M Ca(OH)_(2)` solution

Answer

A, C, D

Explanation

(a) `{:(HCI+,NaCNrarr,NaCI+,HCN),(100xx3xx10^(-3),100xx4.24xx10^(-3),0,0),(=0.3,=0.424, ,),(0,0.124,0.3,0.3):}`
`pH= -log K_(a)+log("salt")/("acid")`
`= -log[4.1xx10^(-10)]+log(0.124)/(0.3)`
`= 9.38+log 0.413`
`= 9.38-0.38=9`
(b) `M` eq.of `NaOH = 2xx10^(-3)xx100=2xx10^(-1)`
`N` of `NaOH = (2xx10^(-1))/(200)= 1xx10^(-3)`
`pOH=3`
`:. pH = 11`
(c ) `[OH^(-)]= sqrt((K_(w))/(K_(a))xxc)= sqrt((10^(-4)xx0.2)/(2xx10^(-5)))= 10^(-5)`
`:. pOH = 5`
`:. pH =9`
(d) `[OH^(-)]= 2xx5xx10^(-6)=10^(-5)M`
`:. pOH =5`
`:. pH = 9`