Question

Using the equation: 2K + 2H2O ---> 2KOH + H2

If 2.5 g of K reacts in 250 ml of water, what mass of H2 is evolved and what is the concentration in g/L of the resultant potassium hydroxide solution?

Answer 1

2K + 2H₂O ---> 2KOH + H₂

Atomic weight of K = 39.098 g/mol

Molecular weight of KOH = 56.10 g/mol

2 moles of K reacts with 2 moles of water to give one mole of H₂

78.196 g of K reacts with 36g of water to give 2g of H₂ or 22.4L of H₂

The mass of H₂ evolved is 2g.

250 mL of water conatins 112.2g of KOH (2 moles of KOH = 2 x 56.10= 112.2g)

1000mL (1L) of water contain 112.2 g x 4 = 448.8g

The concentration in g/L of the resultant potassium hydroxide solution is 448.8g/L