Question

A compound formed of only phosphorous and oxygen is found to be 56.35% phosphorous. What is the empirical formula of the compound?

Answer 1

A compound formed of only phosphorous and oxygen is found to be 56.35% phosphorous. What is the empirical formula of the compound?

Solution 1

$$\mathrm{P_xO_y}$$ $$x : y = \omega(P)/M(P) : \omega(O)/M(O) = 56.35/31 : (100 - 56.35)/16 = 1.8 : 2.7 = 2 : 3$$ $$\mathrm{P_2O_3}$$

Solution 2

Usually O forms compounds as a O²⁺, so we can assume, that formula of the PₓOᵧ is actually P₂Oᵧ, so

$$\omega(P) = 2*M(P)*100\% / 2*M(P) + y*M(O)$$ $$56.35 = 2*31*100 / 2*31 + y*16$$ $$9.016y = 27.063$$ $$y = 3$$ $$\mathrm{P_2O_3}$$