In this stoichiometry problem, determine the theoretical yield:

Excess aqueous copper(II) nitrate reacts with aqueous sodium sulfide to produce aqueous sodium nitrate and copper(II) sulfide as a precipitate. In this reaction 469 grams of copper(II) nitrate were combined with 156 grams of sodium sulfide to produce 272 grams of sodium nitrate.

Respuesta :

yield = 80 %

Explanation:

We have the following chemical reaction:

Cu(NO₃)₂ (aq) + Na₂S (aq) → 2 NaNO₃ (aq) + CuS (s)

where:

(aq) - aqueous

(s) - solid

number of moles = mass / molecular weight

number of moles of Cu(NO₃)₂ = 469 / 187.5 = 2.5 moles

number of moles of Na₂S = 156 / 78 = 2 moles

number of moles of NaNO₃ = 272/ 85 = 3.2 moles (practical)

We see that from the chemical reaction 1 mole of Cu(NO₃)₂ will react with 1 mole of Na₂S. Because we have 2.5 moles of Cu(NO₃)₂ and 2 moles of Na₂S, the limiting reactant will be Na₂S.

Taking this into account, we devise the following reasoning:

if        1 mole of Na₂S produces 2 moles of NaNO₃

then  2 moles of Na₂S produces X moles of NaNO₃

X = (2 × 2) / 1 = 4 moles of NaNO₃ (theoretical)

The yield of the reaction will be:

yield = (practical quantity / theoretical quantity) × 100

yield = (3.2 / 4) × 100 = 80 %

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