Aldehyde with a mass of 23.2 can react with 8.96 liters of hydrogen, determine the formula for the aldehyde.

The reaction equation for the reduction of aldehyde in general form:

RCOH + H2 (cat.) = RCH2OH, where R is a hydrocarbon radical

Let’s find the amount of substance hydrogen:

v (H2) = V (H2) / Vm = 8.96 / 22.4 = 0.4 (mol)

According to the reaction equation, 1 mol of H2 is consumed per 1 mol of RCOH,

therefore v (H2) = v (RCOH) = 0.4 (mol).

Let’s find the molecular weight of the unknown aldehyde:

M (RCOH) = m (RCOH) / v (RCOH) = 23.2 / 0.4 = 58 (amu)

Therefore, the molecular weight of the radical is:

M (R) = M (RCOH) – M (COH) = 58 – 29 = 29 (amu),

which corresponds to ethyl (-C2H5).

Then the formula for the aldehyde is C2H5COH (propanal).