If you reacted 450 g of trimethylgallium with 300 g of arsine, what mass of GaAs could you make?

556.88 g.

Explanation:

Firstly, we need to write the balanced chemical reaction:

(CH₃) ₃Ga + AsH₃ → GaAs + 3 CH₄

It is now a stichiometric oriented problem; 1.0 mole of trimethyl gallium ((CH₃) ₃Ga) reacts with 1.0 mole of arsine (AsH₃) to produce 1.0 mole of gallium arsenide (GaAs) and 3.0 moles of methane (CH₄). Now, we need to calculate the number of moles (n) of the reacting 450.0 g of trimethyl gallium with 300.0 g of arsine using the relation:

n = mass / molar mass,

Molar mass of trimethyl gallium ((CH₃) ₃Ga) = 114.827 g/mol and molar mass of arsine (AsH₃) = 77.95 g/mole. n of trimethyl gallium ((CH₃) ₃Ga) = mass / molar mass = (450.0 g) / (114.827 g/mole) = 3.92 mole. n of arsine (AsH₃) = mass / molar mass = (300.0 g) / (77.95 g/mole) = 3.85 mole. The limiting reactant here is arsine (AsH₃) that it has the lower number of moles. From the stichiometry; 1.0 mole of trimethyl gallium ((CH₃) ₃Ga) reacts with 1.0 mole of arsine (AsH₃) to produce 1.0 mole of gallium arsenide GaAs. Thus, 3.85 mole of arsine (AsH₃) reaacts with 3.92 mole of trimethyl gallium ((CH₃) ₃Ga) (which is slightly excess) to produce 3.85 mole of gallium arsenide (GaAs). Now, we can calculate the mass of the produced gallium arsinate from the relation: mass = n x molar mass. Molar mass of gallium arsenide (GaAs) = 144.645 g/mol. Mass of gallium arsenide (GaAs) = (3.85 mole) (144.645 g/mol) = 556.88 g.