Respuesta :
molar concentration of Na⁺ ions = 3 M
molar concentration of CO₃⁻ ions = 1.5 M
First the water will solvate the sodium carbonate (Na₂CO₃).
Second the 80 mL of water added will dilute the first solution.
Explanation:
When you dissolve the Na₂CO₃ in water, the following solvation process takes place:
Na₂CO₃ (s) + H₂O (l) → 2 Na⁺ (aq) + CO₃⁻ (aq)
To find the final concentration of Na₂CO₃ solution we use the following formula:
concentration (1) × volume (1) = concentration (2) × volume (2)
concentration (2) = concentration (1) × volume (1) / volume (2)
concentration of Na₂CO₃ solution = 2.5 M × 120 mL / 200 mL
concentration of Na₂CO₃ solution = 1.5 M
molar concentration = number of moles / volume (L)
number of moles = molar concentration × volume (L)
number of moles of Na₂CO₃ = 1.5 M × 0.2 L = 0.3 moles
Knowing the solvation process we devise the following reasoning:
if 1 mole of Na₂CO₃ produces 2 moles of Na⁺ ions and 1 mole of CO₃⁻ ions
then 0.3 moles of Na₂CO₃ produces X moles of Na⁺ ions and Y mole of CO₃⁻ ions
X = (0.3 × 2) / 1 = 0.6 moles of Na⁺ ions
Y = (0.3 × 1) / 1 = 0.3 moles of CO₃⁻ ions
molar concentration = number of moles / volume (L)
molar concentration of Na⁺ ions = 0.6 / 0.2 = 3 M
molar concentration of CO₃⁻ ions = 0.3 / 0.2 = 1.5 M
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