Change 6.54 moles of iron (III) sulfide to grams.

Sulfurous acid is formed by the reaction of water and sulfur dioxide.

Balanced reaction will provide the basic information.

Balanced Reaction :

                         SO₂ +  H₂O > H₂SO₃

                        1 mol    1mol                  1mol

From above reaction we come to know

1 mole of H₂O ≅ 1 mole H₂SO₃

if 1 mole of H₂O produces 1 mole of H₂SO₃ then

0.680 mole of water will be required to produces sulfurous acid

Explanation through calculation

apply the unity formula

1 mole of the H₂O ≅ 1 mole of H₂SO₃

x mole of the H₂O ≅  0.680 moles of H₂SO₃

so by cross multiplication

1 mole  x X mole ≅ 1 mole  x 0.680 mole

we have to find moles of H₂O so by rearrangement of the above equation

X mole of H₂O = 1 mole x 0.680 mole

X mole of H₂O =  0.680 moles