Question

Many plants are poisonous because their stems and leaves contain oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4},\) or sodium oxalate, \(\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\) . When ingested, these substances cause swelling of the respiratory tract and suffocation. A standard analysis for determining the amount of oxalate ion, \(\mathrm{C}_{2} \mathrm{O}_{4}^{2-},\) in a sample is to precipitate this species as calcium oxalate, which is insoluble in water. Write the net ionic equation for the reaction between sodium oxalate and calcium chloride, \(\mathrm{CaCl}_{2},\) in aqueous solution.

Short answer

The net ionic equation for the reaction between sodium oxalate (Na2C2O4) and calcium chloride (CaCl2) in aqueous solution is: \(C2O4^{2-} (aq) + Ca^{2+} (aq) \rightarrow CaC2O4 (s)\)

Step-by-step solution

Write the balanced chemical equation

The balanced chemical equation for the reaction between sodium oxalate and calcium chloride is: Na2C2O4 (aq) + CaCl2 (aq) → CaC2O4 (s) + 2 NaCl (aq)

Identify the spectator ions

Spectator ions are ions that remain unchanged during the reaction and do not participate in it. In this case, the spectator ions are sodium (Na⁺) and chloride (Cl⁻) ions.

Write the net ionic equation

To write the net ionic equation, we'll remove the spectator ions from the balanced chemical equation. The net ionic equation is: C2O4²⁻ (aq) + Ca²⁺ (aq) → CaC2O4 (s) This is the net ionic equation for the reaction between sodium oxalate and calcium chloride in aqueous solution.

Key concepts

Oxalate Ion

The oxalate ion, represented as \( \text{C}_2\text{O}_4^{2-} \), is derived from oxalic acid \( \text{H}_2\text{C}_2\text{O}_4 \). It functions primarily as an anion in chemical reactions, which means it carries a negative charge. When substances like oxalic acid or sodium oxalate dissolve in water, they release oxalate ions.

Oxalate ions can be harmful if ingested in large amounts, as they can combine with calcium in the body to form insoluble compounds, potentially leading to health issues such as the formation of kidney stones. This happens because calcium oxalate is insoluble, meaning it does not dissolve well in water, and can accumulate in organs.

In a laboratory analysis, the presence of oxalate ions is often detected by converting them into an insoluble form with a known reagent. For example, in the reaction with calcium chloride, the oxalate ions are precipitated out as calcium oxalate. This precipitation process is helpful in quantifying the amount of oxalate in a sample by isolating it as a solid compound.

Calcium Oxalate

Calcium oxalate \( \text{CaC}_2\text{O}_4 \) is the compound formed when calcium ions \( \text{Ca}^{2+} \) react with oxalate ions \( \text{C}_2\text{O}_4^{2-} \). It forms as an insoluble precipitate in aqueous solutions. This means that it does not readily dissolve.

This precipitation reaction is useful in a variety of analytical procedures. When analyzing samples for oxalate content, calcium chloride is often used because it reacts with oxalate ions to produce a visible solid, calcium oxalate. This allows researchers to filter and weigh the precipitate, thereby determining the amount of oxalate ions present in the original sample.

• Typical reactions involve mixing solutions of a soluble calcium salt, like calcium chloride, with a solution containing oxalate ions.
• The formation of calcium oxalate precipitate is indicative of the presence of oxalate ions and can be used for qualitative identification and quantitative analysis.

Moreover, due to its poor solubility, calcium oxalate also has implications outside of the laboratory. In biology and medicine, calcium oxalate is known for forming kidney stones, a painful condition that can occur when these compounds accumulate in the urinary tract.

Spectator Ions

Spectator ions are ions that exist in the same form on both the reactant and product sides of a chemical equation. In other words, they do not actually participate in the reaction itself. Instead, they remain dissolved in the solution.

In the given reaction between sodium oxalate and calcium chloride, the spectator ions are sodium \( \text{Na}^+ \) and chloride \( \text{Cl}^- \). These ions do not take part in the formation of calcium oxalate and remain in the aqueous solution throughout the reaction.

• Writing net ionic equations involves removing these spectator ions to streamline and highlight the actual chemical change occurring.
• In the mentioned reaction, the net ionic equation is written as \( \text{C}_2\text{O}_4^{2-} (aq) + \text{Ca}^{2+} (aq) \rightarrow \text{CaC}_2\text{O}_4 (s) \), focusing only on the ions that combine to form the precipitate.

Understanding spectator ions is crucial for simplifying chemical equations and concentrating on the core interactions during a chemical reaction. This practice assists in analyzing and predicting the outcomes of reactions, making them more comprehensible even to those new to chemistry.