Determine the mass of hydrogen released by the reaction of 7.8 g of potassium with 50 g of water.

1. Let’s write the equation of interaction of potassium with water:

2K + 2H2O = 2KOH + H2 ↑;

2.Calculate the chemical amount of potassium:

n (K) = m (K): M (K) = 7.8: 39 = 0.2 mol;

3. calculate the chemical amount of water:

n (H2O) = m (H2O): M (H2O) = 50: 18 = 2.78 mol;

4.the lack of potassium is taken, according to it we determine the amount of released hydrogen:

n (H2) = n (K): 2 = 0.2: 2 = 0.1 mol;

5. find the mass of hydrogen:

m (H2) = n (H2) * M (H2) = 0.1 * 2 = 0.2 g.

Answer: 0.2 g.