90.0g of MgCI2 was placed in 50.0cm3 of water to give a saturated solubility of...

JAMB 1998

90.0g of MgCI₂ was placed in 50.0cm³ of water to give a saturated solubility of the salt is 8.0 mol dm³ at the same temperature, what is the mass of the salt left undissolved at the given temperature?

(Mg = 24, Cl = 35.5)

A. 52.0g
B. 58.5g
C. 85.5g
D. 88.5g

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Correct Answer: Option A

Explanation

Molar mass of MgCl₂ = 95g
The solubility of MgCl₂ is 8.0/dm³
1 dm³ = 1000cm³
Solubility of g/cm³
8 x 95 → 1000cm³
x → 50
x = (50)/(1000) x (8 x 95) / (1) = 38g
Mass of the salt left undissolved = 90 - 38 = 52.0g

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