Not 100% sure, but I'd have to say this:
When rounding for sig figs, you look at the other numbers in your calculation and see which one has the least amount of sig figs. This number is 2.70. (3 sig figs). So, you round to 3 significant figures in your calculation.
Hope this helped!
The volume of CO₂ at STP = 2.8 L
<h3>Further explanation</h3>
Given
21 gram of sodium hydrogen carbonate-NaHCO₃
Required
Volume of CO₂
Solution
The decomposition of sodium bicarbonate into sodium carbonate, carbon dioxide, and water :
<em>
2 NaHCO₃(s) → Na₂CO₃(s) + CO₂(g) + H₂O(g)</em>
mol of NaHCO₃ :
= mass : MW NaHCO₃
= 21 g : 84 g/mol
= 0.25
From the equation, mol ratio of NaHCO₃(s) :CO₂(g) = 2 : 1, so mol CO₂ :
= 1/2 x mol NaHCO₃
= 1/2 x 0.25
= 0.125
At STP, 1 mol gas = 22.4 L, so for 0.125 mol :
= 0.125 x 22.4 L
= 2.8 L
