Calculate pH for:
(a) `0.01N Ca(OH)_(2)`
(b) `0.01M Ca(OH)_(2)`
(c ) `0.0008M Mg(OH)_(2)`
Assume complete ionisation of each.

Explanation

(a) `0.01N Ca(OH)_(2):`
`{:(Ca(OH)_(2),rarrCa^(2+)+,2OH^(-)),(10^(-2)N,0,0),(0,10^(-2),10^(2-)):}`
Eq. ratio of `Ca(OH)_(2): Ca^(2+):OH^(-1)::1:1:1`
`(.: "Equivalent litre"^(-1)"are given")`
`:. [OH^(-)]=10^(-2)M`
`:. pOH=2`
`:. pH=12`
(b) `0.01M Ca(OH)_(2)`:
`{:(Ca(OH)_(2)rarr,Ca^(2+)+,2OH^(-)),(10^(-2)M,0,0),(0,10^(-2),2xx10^(-2)):}`
Mole ratio of `Ca(OH)_(2):Ca^(2+):OH^(-1):1:1:2`
`:. [OH^(-)]=2xx10^(-2)M`
`:. pOH=1.6989`
`:. pH=14-1.6989=12.3011`
(c ) `0.0008M Mg(OH)_(2):`
`{:(Mg(OH)_(2)rarr,Mg^(2+)+,2OH^(-)),(8xx10^(-4)M,0,0),(0,8xx10^(-4),2xx8xx10^(-4)):}`
`:.[OH^(-)]=16xx10^(-4)M`
`:. pOH=2.7958`
`:. pH=11.2042`