Question

determining the decomposition of nahco₃
conclusion
initial mass: 7.53 g
final mass 2.8 g
reaction i:
theoretical yield = 3.59g
nahco₃(s) → naoh(s) + co₂(g)
reaction ii:
theoretical yield = 2.78 g
2nahco₃(s) → na₂o(s) + 2co₂(g) + h₂o(g)
reaction iii:
theoretical yield = 4.75 g
2nahco₃(s) → na₂co₃(s) + co₂(g) + h₂o(g)
assuming the reaction went to completion, which of the three reactions correctly identifies the decomposition of the sodium bicarbonate under high heat?
2nahco₃(s) → na₂co₃(s) + co₂(g) + h₂o(g)
nahco₃(s) → naoh(s) + co₂(g)
2nahco₃(s) → na₂o(s) + 2co₂(g) + h₂o(g)

Explanation:

To determine the correct reaction, we compare the final mass (2.8 g) with the theoretical yields of each reaction:

• Reaction I (NaHCO₃ → NaOH + CO₂) has a theoretical yield of 3.59 g, which is not close to 2.8 g.
• Reaction II (2NaHCO₃ → Na₂O + 2CO₂ + H₂O) has a theoretical yield of 2.78 g, very close to 2.8 g.
• Reaction III (2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O) has a theoretical yield of 4.75 g, not close to 2.8 g.

The reaction with a theoretical yield matching the final mass (2.8 g) is Reaction II: \( \boldsymbol{2\text{NaHCO}_3(\text{s})
ightarrow \text{Na}_2\text{O}(\text{s}) + 2\text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{g})} \) (though the option label for Reaction II’s equation is miswritten as “2NaHCO₃(s) → Na₂O(s) + 2CO₂(g) + H₂O(g)” in the choices, this matches the theoretical yield).

Answer:

The correct reaction is the one with the equation \( 2\text{NaHCO}_3(\text{s})
ightarrow \text{Na}_2\text{O}(\text{s}) + 2\text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{g}) \) (the middle option in the list, labeled as the second choice: “\( \text{NaHCO}_3(\text{s})
ightarrow \text{NaOH}(\text{s}) + \text{CO}_2(\text{g}) \)” is incorrect; the correct one is the second option’s equation (despite the label mismatch) or the third option? Wait, recheck:

Wait, the final mass is 2.8 g. Reaction II (the second reaction listed on the left) has a theoretical yield of 2.78 g, which is closest to 2.8 g. The left side lists:

• Reaction I: \( \text{NaHCO}_3

ightarrow \text{NaOH} + \text{CO}_2 \), yield 3.59 g.

• Reaction II: \( 2\text{NaHCO}_3

ightarrow \text{Na}_2\text{O} + 2\text{CO}_2 + \text{H}_2\text{O} \), yield 2.78 g.

• Reaction III: \( 2\text{NaHCO}_3

ightarrow \text{Na}_2\text{CO}_3 + \text{CO}_2 + \text{H}_2\text{O} \), yield 4.75 g.

The right-side options are:

1. \( 2\text{NaHCO}_3(\text{s})

ightarrow \text{Na}_2\text{CO}_3(\text{s}) + \text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{g}) \) (Reaction III’s equation, yield 4.75 g, no).

1. \( \text{NaHCO}_3(\text{s})

ightarrow \text{NaOH}(\text{s}) + \text{CO}_2(\text{g}) \) (Reaction I’s equation, yield 3.59 g, no).

1. \( 2\text{NaHCO}_3(\text{s})

ightarrow \text{Na}_2\text{O}(\text{s}) + 2\text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{g}) \) (Reaction II’s equation, yield 2.78 g, matches 2.8 g).

So the correct option is the third one: \( 2\text{NaHCO}_3(\text{s})
ightarrow \text{Na}_2\text{O}(\text{s}) + 2\text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{g}) \) (the bottom option in the list).