40 ml of `0.1` M ammonia is mixed with 20 ml of `0.1 M HCI`. What is the pH of the mixture ? (`pK_(b)` of ammonia solution is `4.74.`)

Options

A. 4.74
B. 2.36
C. 9.26
D. `5.00`

Answer

c

Explanation

40 ml. of `0.1` M ammonia solution `=40xx0.1`
= 4 mili equivalent ammonia solution
`20" ml of 0.1 M HC "20xx0.1`
= 2 mili equivalent of HCI
`NH_(4)OH+HCI to NH_(4) +H_(2)O`
`{:("Initial mili eqv",4,2,0),("Mili-eqv. after",4-2,0,2):}`
reaction=2
`:. rho OH=K_(b)+"log"_(10)([NH_(4)CI])/([NH_(4)OH])=4.74 "log" (2)/(2)`
`=4.74+log 1= 4.74`
`:. p H=14-4.74=9.26`