The number of liter of hydrogen gas that are formed at STP is
15.344 L
calculation
2 Na +2 H₂O → 2NaOH +H₂
calculate the moles of Na
moles =mass/molar mass
from periodic table the molar mass of Na = 23 g/mol
moles = 31.5 g /23 g /mol = 1.37 moles
From equation above the mole ratio of Na: H2 is 2:1
therefore the moles of H2 =1.37 x1/2 =0.685 moles
At STP 1 moles of a gas = 22.4 L
0.685 moles = ? L
by cross multiplication
=[ (0.685 moles x 22.4 L) / 1 mole =15.344 L
The percent yield = 84.77%
calculation
4 Na + O₂ → 2 Na₂O
%yield =actual yield / theoretical yield x 100
Actual yield= 61.8 g
The theoretical yield is calculated as below
Step 1: find the moles of Na
moles = mass /molar mass
from periodic table the molar mass of Na = 23 g/mol
moles = 54.1 g /23 g/mol =2.352 moles
Step 2: use the mole ratio to determine the moles of Na₂O
Na:Na₂O is 4: 2 therefore the moles of Na₂O = 2.352 x 2/4 =1.176 moles
Step 3: find the theoretical mass of Na₂O
mass = moles x molar mass
The molar mass of Na₂O = [(23 x 2 ) + 16] =62 g/mol
mass = 1.176 moles x 62 g/mol = 72.9 g
% yield is therefore = 61.8 g /72.9 x 100 = 84.77%
