K text sp of Mg ( OH )2 is 4.0 × 10-6. At what minimum pH, Mg 2+ ions starts precipitating 0.01 MgCl

Question

K text sp of Mg ( OH )2 is 4.0 × 10-6. At what minimum pH, Mg 2+ ions starts precipitating 0.01 MgCl (A) 2+ log 2 (B) 2- log 2 (C) 12+ log 2 (D) 12- log 2

Tardigrade Admin · Accepted Answer

Precipitation starts when Q sp =K sp : K sp =[ Ca 2+][ oversetΘOH 2]2 ∴[ oversetΘ OH ]=((4 × 10-6/0.01))1 / 2=2 × 10-2 pOH =- log 2+2 pH = i 4-[- log 2+2]=12+ log 2

Q. $K_{sp}$ of $M g (O H)_{2}$ is $4.0 \times 1 0^{- 6}$ . At what minimum $p H$ , $M g^{2 +}$ ions starts precipitating $0.01 M g Cl$

$2 + lo g 2$

$2 - lo g 2$

$12 + lo g 2$

$12 - lo g 2$

Precipitation starts when $Q_{s p} = K_{s p}$ :
$K_{s p} = [C a^{2 +}] [O Θ H^{2}]^{2}$
$∴ [O H Θ] = (\frac{4 \times 1 0 ^{- 6}}{0.01})^{1/2} = 2 \times 1 0^{- 2}$
$pO H = - lo g 2 + 2$
$p H = i 4 - [- lo g 2 + 2] = 12 + lo g 2$

Q. Ksp ​ of Mg(OH)2​ is 4.0×10−6. At what minimum pH, Mg2+ ions starts precipitating 0.01MgCl

2+log2

2−log2

12+log2

12−log2