Question

Read the given equation. 2Na + 2H2O → 2NaOH + H2

Answer 1

Answer:

B) 12.9 grams.

Explanation:

How many moles of molecules in that 6.30 L of H₂?

The volume of one mole of an ideal gas at STP (0 °C, 1 atm) is 22.4 liters.

(The volume of that one mole of gas at STP will be 22.7 liters if STP is defined as 0 °C and 10⁵ Pa).

$\displaystyle n(\text{H}_2) = \frac{6.30\;\text{L}}{22.4\;\text{L}\cdot\text{mol}^{-1}} = 0.28125\;\text{mol}$.

How many moles of Na will be needed?

The coefficient in front of Na in the equation is twice the coefficient in front of H₂. It takes two moles of Na to produce one mole of H₂.

$n(\text{Na}) = 2\;n(\text{H}_2) = 2\times 0.28125= 0.5625\;\text{mol}$.

What's the mass of that many Na atoms?

Refer to a modern periodic table. The molar mass of ₁₁Na is 22.990. The mass of one mole of Na atoms is 22.990 gram. The mass of 0.5625 moles of Na atoms will be

$m = n\cdot M = 0.5625 \times 22.990 = 12.9\;\text{g}$.

(2 sig. fig. as in the volume of the H₂ gas.)