Question

Solid sodium reacts violently with water, producing heat, hydrogen gas, and sodium hydroxide. How many molecules of hydrogen gas are formed when 48.7 g of sodium are added to water? Write a balanced equation and then solve.

Answer 1

Balanced reaction is:

2Na + 2H₂O ------>  2NaOH + H₂

Assume the sodium is limiting reagent:

number of moles of sodium = mass / molar mass

= 48.7 g / 23.0 g/mol

= 2.12 moles Na

According to above chemical reaction,

From 2 mol Na, 1 mol H₂ is produced.

So, From 1 mol Na = 1 mol H₂/2 mol Na

From 2.12 mol Na = 2.12 mol Na *1 mol H₂/2 mol Na

= 1.06 mol H₂

Now, 1 mol H₂=6.023*10²³ molecules

1.06 mol H₂= 1.06 *6.023*10²³ molecules H₂

= 6.384*10²³ molecules H₂