Find the volume of hydrogen released by the interaction of 3.9 g of potassium with hydrobromic acid.

Let’s write down the reaction equation, arrange the coefficients:
2K + 2HBr = 2KBr + H2 – redox reaction, hydrogen is released;
M (K) = 39.1 g / mol;
M (H2) = 2 g / mol;
Determine the amount of potassium moles if the mass is known:
Y (K) = m / M = 3.9 / 39 = 0.09 mol;
Let’s make a proportion according to the equation:
0.09 mol (K) – X mol (H2);
-2 mol -1 mol hence, X mol (H2) = 0.09 * 1/2 = 0.049 mol;
Let’s calculate the volume of hydrogen:
V (H2) = 0.049 * 22.4 = 1.09 liters.
Answer: during the reaction, 1.09 liters of hydrogen is released.