Question

How many grams of O2 will completely react with 49.0 g PH3?

Answer 1

2PH₃ + 4O₂ → P₂O₅ + 3H₂O

M(PH₃) = 40 g/mol

M(O₂) = 32 g/mol

n = m/M

n(PH₃) = 49/40 = 1.225 mole

n(O₂) = 2n(PH₃) $= 2\times 1.225 = 2.45 \; mol$

$m = n\times M$

m(O₂) $= 2.45 \times 32 = 78.4 \;g$