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 and calcium chloride in aqueous solution is: \(C2O4^{2-}(aq) + Ca^{2+}(aq) \rightarrow CaC2O4(s)\).

Step-by-step solution

Write the balanced chemical equation for the reaction

First, we will write the balanced chemical equation for the reaction between sodium oxalate (Na2C2O4) and calcium chloride (CaCl2). Remember that the products of a double displacement reaction are formed by exchanging the cations and anions of the reactants. Na2C2O4 (aq) + CaCl2 (aq) -> CaC2O4 (s) + 2NaCl (aq)

Write the complete ionic equation

Now, we will write the complete ionic equation by breaking down the soluble ionic compounds (sodium oxalate and calcium chloride) into their respective cations and anions. 2Na⁺(aq) + C2O4²⁻(aq) + Ca²⁺(aq) + 2Cl⁻(aq) -> CaC2O4(s) + 2Na⁺(aq) + 2Cl⁻(aq)

Write the net ionic equation

Finally, we will write the net ionic equation by canceling out the spectator ions, which are the ions that do not participate in the reaction. In this case, the spectator ions are 2Na⁺(aq) and 2Cl⁻(aq). C2O4²⁻(aq) + Ca²⁺(aq) -> CaC2O4(s) So the net ionic equation for the reaction between sodium oxalate and calcium chloride in aqueous solution is: C2O4²⁻(aq) + Ca²⁺(aq) -> CaC2O4(s)

Key concepts

Understanding Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They depict the substances involved and their transformations during the reaction. In a chemical equation, the substances that start the reaction, called reactants, are listed on the left, while the substances formed, called products, appear on the right.
The arrow (\( \rightarrow \)) is used to show the direction of the reaction. Chemical equations must be balanced, meaning they should have the same number of each type of atom on both sides. This reflects the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.
To balance an equation:

• Identify the number of atoms of each element in reactants and products.
• Use coefficients to adjust the numbers of molecules of each substance as needed to balance the atoms.
• Ensure the total charge is the same on both sides if the reaction involves ions.

Writing balanced chemical equations is essential for accurately representing and predicting the outcomes of chemical reactions.

Exploring Double Displacement Reactions

Double displacement reactions, also known as double replacement reactions or metathesis reactions, involve the exchange of ions between two reacting compounds. This type of reaction typically produces a precipitate, water, or a gas as a product.
In a double displacement reaction:

• Two ionic compounds react to form two new compounds.
• The cations (positive ions) and anions (negative ions) swap partners.
• They generally occur in aqueous solutions, where the ions are free to move.

Consider the reaction of sodium oxalate with calcium chloride:\[\text{Na}_2\text{C}_2\text{O}_4 \text{(aq)} + \text{CaCl}_2 \text{(aq)} \rightarrow \text{CaC}_2\text{O}_4 \text{(s)} + 2 \text{NaCl} \text{(aq)}\]Here, sodium (Na⁺) exchanges partners with calcium (Ca²⁺), forming the insoluble calcium oxalate precipitate and soluble sodium chloride.
Understanding these reactions is key when predicting the formation of precipitates and understanding solution chemistry.

Identifying Spectator Ions

Spectator ions are ions present in a reaction mixture that do not participate in the actual chemical change. They exist in the same form on both sides of a chemical equation.
When writing net ionic equations, spectator ions are excluded because they do not affect the overall reaction. This simplification focuses only on the ions and molecules directly involved in forming the products. Let's take a look at the example reaction:

• Complete ionic equation: \[2\text{Na}^+ \text{(aq)} + \text{C}_2\text{O}_4^{2-} \text{(aq)} + \text{Ca}^{2+} \text{(aq)} + 2\text{Cl}^- \text{(aq)} \rightarrow \text{CaC}_2\text{O}_4 \text{(s)} + 2\text{Na}^+ \text{(aq)} + 2\text{Cl}^- \text{(aq)}\]
• Net ionic equation (after removing spectator ions): \[\text{C}_2\text{O}_4^{2-} \text{(aq)} + \text{Ca}^{2+} \text{(aq)} \rightarrow \text{CaC}_2\text{O}_4 \text{(s)}\]

In this example, sodium ions (Na⁺) and chloride ions (Cl⁻) are the spectator ions. They remain unchanged and are not directly involved in forming the solid calcium oxalate. Identifying and eliminating spectator ions simplifies the chemical equation, making it easier to understand the essential reaction taking place.