What is the net ionic equation of 2H+ + SO42- + Ca2+ + 2I- -> CaSO4 + 2H+ + 2I-?
The correct answer and explanation is:
Net Ionic Equation:
The given reaction is:
2H⁺ + SO₄²⁻ + Ca²⁺ + 2I⁻ → CaSO₄ + 2H⁺ + 2I⁻
Step 1: Cancel Spectator Ions
On both sides of the equation, we see 2H⁺ and 2I⁻. These ions appear unchanged and do not participate in the actual chemical change. These are spectator ions and can be canceled out from both sides of the equation.
This simplifies the reaction to:
SO₄²⁻ + Ca²⁺ → CaSO₄ (s)
✅ Correct Net Ionic Equation:
Ca2+(aq)+SO42−(aq)→CaSO4(s)\boxed{\text{Ca}^{2+} (aq) + \text{SO}_4^{2-} (aq) \rightarrow \text{CaSO}_4 (s)}
Explanation (Approx. 300 Words):
A net ionic equation shows only the chemical species involved in the actual chemical change, excluding spectator ions that remain unchanged during the reaction.
In this reaction:
- Calcium ion (Ca²⁺) and sulfate ion (SO₄²⁻) combine to form calcium sulfate (CaSO₄), a precipitate (solid).
- The other ions present, H⁺ and I⁻, are present on both sides of the equation and remain in aqueous form, not participating in the formation of the precipitate. Thus, they are considered spectator ions.
The key concept here is precipitation. When two aqueous solutions are mixed, if the product is an insoluble salt, it will precipitate out of solution. According to solubility rules, most sulfates are soluble, but calcium sulfate is only slightly soluble and can precipitate under the right conditions.
The original reaction likely takes place in an aqueous solution where soluble ionic compounds dissociate into their respective ions. When Ca²⁺ and SO₄²⁻ meet, they form a solid CaSO₄, removing them from the solution. This is the driving force behind the reaction.
By writing the net ionic equation, we focus on what actually changes in the reaction. The result highlights the formation of a new substance, CaSO₄, while ignoring unchanged ions. This simplification helps chemists understand the core chemical change and is especially useful when predicting the outcomes of double displacement or precipitation reactions.