How many grams of hydroxide is formed when 11.5 g of sodium reacts with water?

Let’s write the reaction equation:
2Na + 2H2O = 2NaOH + H2 ↑
Let’s find the amount of sodium substance:
v (Na) = m (Na) / M (Na) = 11.5 / 23 = 0.5 (mol).
According to the reaction equation, 2 mol of NaOH is formed from 2 mol of Na, therefore:
v (NaOH) = v (Na) = 0.5 (mol).
Thus, the mass of the resulting sodium hydroxide:
m (NaOH) = v (NaOH) * M (NaOH) = 0.5 * 40 = 20 (g).
Answer: 20 g.