Oxygen with a mass of 10 g and hydrogen with a mass of 0.2 g were mixed and the resulting mixture was set on fire

Oxygen with a mass of 10 g and hydrogen with a mass of 0.2 g were mixed and the resulting mixture was set on fire. Find the number of water molecules formed.

Given:
m (O2) = 10 g
m (H2) = 0.2 g
To find:
N (H2O) -?
Decision:
1) Write the equation of a chemical reaction:
O2 + 2H2 => 2H2O;
2) Calculate the amount of substance O2:
n (O2) = m (O2) / M (O2) = 10/32 = 0.31 mol;
3) Calculate the amount of substance H2:
n (H2) = m (H2) / M (H2) = 0.2 / 2 = 0.1 mol;
4) Determine the amount of substance H2O:
n (H2O) = n (H2) = 0.1 mol;
5) Calculate the number of H2O molecules:
N (H2O) = n (H2O) * NA = 0.1 * 6.02 * 10 ^ 23 = 6.02 * 10 ^ 22.
Answer: The number of H2O molecules is 6.02 * 10 ^ 22.