Question

When heated, NaOH decomposes according to the following equation. If all of the water is produced as water vapor, what is the expected mass loss for a 7.95 gram sample of NaOH? Report your answer with three significant figures.

2 NaOH (s) → Na₂O (s) + H₂O (g)

Answer 1

Solution : As we know that

No. Of moles = mass /molar mass

Therefore

No. Of moles of NaOH = 7.95 g/ 40g mol-1​​​​​​

= 0.198 mol

Now

Given reaction is

2 NaOH (s) Na2O (s) +H2O (g)

From the reaction we see that

2 mol of NaOH gives 1 mol of H2O

Therefore

No. Of moles of H​​​​​​2O =1/2 * No. Of moles of NaOH

No. Of moles of H2O = 0.198/2

= 0.099 mol

Therefore

Mass of H2O formed = 0.099 mol * 18.0 g mol-1​​​​​​

= 1.78 g

Thus

Mass of NaOH loss = mass of H2O formed

=1.78 g