Question

multiple choice 1 point
for the reaction represented by the equation ( 2na + 2h_2o \to 2naoh + h_2 ), how many grams of hydrogen are produced if 120. g of sodium and 80. g of water are available?

1. g

200 g
4.5 g

Explanation:

Step1: Calculate moles of Na and H₂O

Molar mass of Na is \(23\ g/mol\), moles of \(Na=\frac{120\ g}{23\ g/mol}\approx5.22\ mol\).
Molar mass of \(H_2O\) is \(18\ g/mol\), moles of \(H_2O=\frac{80\ g}{18\ g/mol}\approx4.44\ mol\).
From the equation \(2Na + 2H_2O
ightarrow2NaOH + H_2\), the mole ratio of \(Na:H_2O = 1:1\). So \(Na\) is in excess.

Step2: Calculate moles of H₂ using H₂O

From the equation, mole ratio of \(H_2O:H_2 = 2:1\).
Moles of \(H_2=\frac{1}{2}\times\) moles of \(H_2O=\frac{1}{2}\times4.44\ mol = 2.22\ mol\).

Step3: Calculate mass of H₂

Molar mass of \(H_2\) is \(2\ g/mol\), mass of \(H_2=2.22\ mol\times2\ g/mol = 4.44\ g\approx4.5\ g\).

Answer:

4.5 g