A naughty student tries to poison his teacher's pot plants with aqueous acid laced fertilizer. Realising that the acid (HX - molar mass 27 g / mol ) is potentially dangerous to human (quite volat

Question

A naughty student tries to poison his teacher's pot plants with aqueous acid laced fertilizer. Realising that the acid (HX - molar mass 27 g / mol ) is potentially dangerous to human (quite volatile). He realises that he needs the free anion ( X − ) concentration in his fertilizer to be 0.0002 M . First he does a quick test if he adds 0.54 g of HX to 100 ml of water, the pH is measured to be 3.7. How many grams HX should he add to 10 L in order to prepare his fatal fertilizer ? [Take : lo g 2 = 0.3 ]

TestHub · Accepted Answer

n HX ​ = 27 0.54 ​ mol = 0.02 mol ∴ [ HX ] = 0.1 0.02 ​ M = 0.2 M pH = 3.7 ⇒ [ H + ] = 2 × 1 0 − 4 M ∴ H X → H + + X − ⇒ [ X − ] = [ H + ] = 2 × 1 0 − 4 = 0.0002 M ∴ [ HX ] = 0.2 M ∴ In 10 L , n HX ​ = 0.2 × 10 mol = 2 mol ∴ m HX ​ = 2 × 27 g = 54 g

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