Paragraph: 6 gm of magnesium ( Mg ) is burnt with insufficient amount of oxygen. The residue is treated with 100 ml of H ₂ SO ₄ solution ( 30 % by mass, 1.4 gm / ml density), resulting in an evolution of 3.36 litre of H ₂ gas at STP. After

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Paragraph: 6 gm of magnesium ( Mg ) is burnt with insufficient amount of oxygen. The residue is treated with 100 ml of H ₂ SO ₄ solution ( 30 % by mass, 1.4 gm / ml density), resulting in an evolution of 3.36 litre of H ₂ gas at STP. After the reaction, density of H ₂ SO ₄ solution is found to be 1.25 gm / ml . Assume no change in volume of H ₂ SO ₄ solution. Question: Percentage w / w of final H ₂ SO ₄ solution is :

Quantrex Academy · Accepted Answer

Correct answer: C. 14

Mg + 1 2 O ₂ MgO 0.1 ~mol 0.1 ~mol aligned & Mg + H ₂ SO ₄ MgSO ₄+ H ₂ & 0.15 ~mol 0.15 ~mol aligned aligned & MgO + H ₂ SO ₄ MgSO ₄+ H ₂ O & 0.1 ~mol & ( ~W _ H ₂ SO ₄ )_ i =100 1.4 0.3=42 gm & ( ~W _ H ₂ SO ₄ )_ f =42-0.25 98=17.5 gm aligned (a) % w / w of final H ₂ SO ₄ solution = 17.5 100 1.25 100=14 % (b) W _ O ₂ used = 0.1 2 32=1.6 gm

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