Calculate the mass of hydrogen that can be added to 5.6 g of ethene.

Hydrogenation of ethylene to ethane.
CH2 = CH2 + H2 => C2H6.
According to the reaction, the number of moles of all substances will be equal.
n (C2H4) = m / Mr = 5.6 g / 28 g / mol = 0.2 mol.
n (H2) = n (C2H4) = 0.2 mol.
The mass of hydrogen required to recover ethylene.
m (H2) = n • Mr = 0.2 mol • 2 g / mol = 0.4 g / mol.

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