Multiple choice

A mixture of 4 g of H2 and 128 g of HI is prompted in a 2 litre flask. What will be its respective active mass?

  1. 0.5 mol L-1

  2. 0.05 mol L-1

  3. 0.005 mol L-1

  4. 0.0005 mol L-1
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A Correct answer
Explanation

Mass of hydrogen = 4 g, Mol. mass of hydrogen = 2; Volume of the flask = 2 litres. Active mass of hydrogen = 4/2 X 2 = 1 mol L-1; Mass of HI = 128 g, Mol. mass of HI = 128 g, Volume of the flask = 2 litre. Active mass of hydrogen iodide = 128/(128 X 2) = 0.5  mol L-1                                                      

AI explanation

Active mass (molar concentration) is moles of substance divided by volume in litres. HI has a molar mass of 128 g/mol, so 128 g equals 1 mole; dividing by the 2 L flask volume gives 0.5 mol/L. This is the standard way to convert a given mass of gas into its concentration for equilibrium calculations.

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