1.

Which of the following concentrations of NH_(4)^(+) will be sufficient to prevent the precipitation of Mg(OH)_(2) form a solution which is 0.01 M MgCl_2 and 0.1 M NH_3(aq.) Given that :K_(SP) of Mg(OH)_(2)=2.5xx10^(-11) and K_b for NH_3(aq)=2xx10^(-5)

Answer»

0.01 M
0.02 M
0.001 M
0.04 M

Solution :`K_(SP)=[Mg^(+2)][OH^(-)]^2`
`[OH^(-)]=SQRT((2.5xx10^(-11))/0.01)=5xx10^(-5)`
`K_b=([NH_4^+][OH^(-)])/([NH_3])`
So, `[NH_4^+]=0.04 M`


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