Calculate the mass of oxygen formed during the decomposition of 180 g of water.

Given:

m (H2O) = 180 g;

To find:

m (O2) -?

Solution:

1) We compose the reaction equation corresponding to the condition of the given problem:

2H2O – (electric current) -> 2H2 + O2;

2) Find the amount of water contained in 180 grams of liquid:

n (H2O) = m: M = 180 g: 18 g / mol = 10 mol;

3) We compose logical equality:

if 2 mol H2O gives 1 mol O2,

then 10 mol H2O will give x mol O2,

then x = 5 mol.

4) Find the mass of oxygen released as a gas as a result of the reaction:

m (O2) = n * M = 5 mol * 32 g / mol = 160 g.

Answer: m (O2) = 160 g.