The correct option is D None of the above
(a) 10−9 M HCl is a very dilute solution where water dissociation needs to be considered to calculate the total [H+] ions present in the solution.
[H+] from HCl = 10−9 M
[H+] from H2O = 10−7 M
Total [H+]=(10−9+10−7)=1.01×10−7 M
We know that pH=−log10[H+]
pH=−log10(1.01×10−7)=6.99.
(b) Ba(OH)2 is a strong base and in 1 liter aqueous solution 1 mol Ba(OH)2 dissociates to give 2 mol OH− ions.
∴[OH−]=4×10−3M⇒[H+][OH−]=10−14⇒[H+]=2.5×10−12M⇒pH=−log10[H+]=−log10(2.5×10−12)=11.60
(c)
[OH−] from H2O = 10−7 M
Total [OH−]=(10−9+10−7)=1.01×10−7 M
We know that pOH=−log10[OH−]
pOH=−log10(1.01×10−7)=6.99pH+pOH=14pH=14−6.99=7.01
Therefore none of these options are correct.