Question

Based on the table, answer the following

a) A student claims that the reaction is an oxidation reduction reaction because the oxidation number of carbon changes. Do you agree with the claim?
b) calculate number of moles of NaHCO3 present in the mixture in the test tube before the reaction was initiated

Answer 1

1. No. The oxidation number of C is not changed. This is not a redox reaction since there is no oxidation or reduction.

The balanced equation for the heating of NaHCO₃ is
2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

Sum of each elements' oxidation number = charge of the compound

For NaHCO₃,
Na = +1 H = +1 O = -2 C = a

1 + 1 + a + (-2) x 3 = 0
2 + a - 6 = 0
a = +4

For Na₂CO₃,
Na = +1 O = -2 C = b

1 x 2+ b + (-2) x 3 = 0
2 + b - 6 = 0
b = +4

For CO₂,
O = -2 C = z

z + (-2) x 2 = 0
z - 4 = 0
z = +4

a = b= z = +4

Hence, oxidation number of C is not changed.

2. The reaction is
2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

By drying agent, the produced H₂O is removed by absorbing.

Then mass of produced H₂O = Final mass of drying agent - initial mass
= 2.303 g - 2.134 g
= 0.169 g
Molar mass of H₂O = 18 g/mol

Hence, moles of produced H₂O = 0.169 g / 18 g/mol
= 9.39 x 10⁻³ mol

The stoichiometric ratio between NaHCO₃ and H₂O is 2 : 1

Hence, moles of NaHCO₃ = moles of H₂O x 2
= 9.39 x 10⁻³ mol x 2
= 0.01878 mol

Hence, 0.01878 moles of NaHCO₃ present initially.

(Assume that all NaHCO₃ are heated during 10 minutes)