The empirical formula for biomass of an unknown organism is $CH_{1.8}O_{0.5}N_{0.2}$. To grow this organism, ethanol $(C_2H_5OH)$ and ammonia are used as carbon and nitrogen sources, respectively. Assume no product formation other than biomass. To produce $1$ mole of biomass from $1$ mole of ethanol, the number of moles of oxygen required will be __________