Question

Many plants are poisonous because their stems and leaves contain oxalic acid $\left({\mathrm{H}}_2{\mathrm{C}}_2{\mathrm{O}}_4\right)$ or sodium oxalate $\left({\mathrm{Na}}_2{\mathrm{C}}_2{\mathrm{O}}_4\right)$; when ingested, these substances cause swelling of the respiratory tract and suffocation. A standard analysis for determining the amount of oxalate ion $\left({\mathrm{C}}_2{\mathrm{O}}_4{}^{2-}\right)$ 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 $\left({\mathrm{CaCl}}_2\right)$ in aqueous solution.

Short answer

The net ionic equation for the reaction between sodium oxalate and calcium chloride in aqueous solution is: $2C_2{O}_4^{2-}(aq)+C{a}^{2+}(aq)\to Ca{C}_2{O}_4(s)$

Step-by-step solution

Write the balanced chemical equation

First, we need to write down the balanced chemical equation for the reaction between sodium oxalate and calcium chloride in aqueous solution. Sodium oxalate is a salt of sodium (Na^+) and oxalate ion (C2O4^2-), and calcium chloride is a salt of calcium (Ca^2+) and chloride ion (Cl^-). In this reaction, calcium (Ca^2+) will replace sodium (Na^+) in sodium oxalate, forming calcium oxalate (which is insoluble in water) and sodium chloride (a soluble salt). The balanced chemical equation for this reaction is: $N{a}_2{C}_2{O}_4+CaC{l}_2\to Ca{C}_2{O}_4\downarrow +2NaCl$

Convert the balanced chemical equation into a net ionic equation

Now, we need to convert the balanced chemical equation into a net ionic equation by removing the spectator ions. Spectator ions are ions that do not participate in the reaction and remain unchanged in the products. In this reaction, sodium (Na^+) and chloride (Cl^-) ions are the spectator ions, as they do not participate in the formation of the solid precipitate, calcium oxalate. The net ionic equation will only show the ions that participate in the reaction: $2C_2{O}_4^{2-}+C{a}^{2+}\to Ca{C}_2{O}_4\downarrow$

Write the net ionic equation for the reaction

Finally, having removed the spectator ions, we can now write down the net ionic equation for the reaction between sodium oxalate and calcium chloride in aqueous solution as follows: $2C_2{O}_4^{2-}(aq)+C{a}^{2+}(aq)\to Ca{C}_2{O}_4(s)$

Key concepts

Oxalate Ion Determination

Oxalate ion determination is an important procedure in chemistry, especially when assessing the levels of potentially toxic compounds in plants or biological samples. The oxalate ion ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$, commonly found in both oxalic acid and sodium oxalate, can form insoluble precipitates with calcium ions. This property is utilized in analytical chemistry to measure the concentration of oxalate ions in a given sample, ensuring safety in food products and pharmaceutical preparations.A common process for determining oxalate concentration involves the precipitation of calcium oxalate. By adding a reagent containing calcium ions, such as calcium chloride, to a sample solution, the oxalate ions form a precipitate. The resulting solid, calcium oxalate, can then be filtered out, dried, and weighed to determine the oxalate concentration. This method is both precise and reliable.The analysis often requires careful control of conditions such as pH and temperature to ensure complete precipitation. Additionally, the knowledge of the solubility product of calcium oxalate is crucial as it allows quantitative conversion of soluble oxalate ions into a measurable solid precipitate.

Precipitation Reaction

Precipitation reactions occur when two aqueous solutions react to form an insoluble solid, or precipitate. This is a double displacement reaction where the cations and anions swap places, resulting in the formation of an insoluble compound in solution. For instance, when sodium oxalate $({\mathrm{Na}}_2{\mathrm{C}}_2{\mathrm{O}}_4)$ is mixed with calcium chloride $({\mathrm{CaCl}}_2)$, the calcium ions ${\mathrm{Ca}}^{2+}$ and oxalate ions ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$ react to form calcium oxalate $({\mathrm{CaC}}_2{\mathrm{O}}_4)$.Using the previously discussed example, the occurrence of a precipitation reaction can be summarized as follows:

• Mix two soluble salts in water, such as sodium oxalate and calcium chloride.
• Observe the formation of a solid precipitate, calcium oxalate, which is insoluble.
• Remove and quantify the precipitate to analyze the initial components.

This focused approach provides an efficient way to separate and quantify specific ions in solution, making precipitation reactions a cornerstone of analytical procedures in chemistry.

Spectator Ions

In many chemical reactions, especially in aqueous solutions, not all ions directly participate in the formation of the final product. These non-participating ions are known as spectator ions. They remain unaltered in solution before and after the reaction, merely "watching" the actual chemical change occur without contributing.For example, in the reaction between sodium oxalate and calcium chloride, the sodium ions ${\mathrm{Na}}^{+}$ and chloride ions ${\mathrm{Cl}}^{-}$ remain in solution as spectator ions. The net ionic equation is simplified to reflect only the species that change, specifically:$$2{\mathrm{C}}_2{\mathrm{O}}_4^{2-}(aq)+{\mathrm{Ca}}^{2+}(aq)\to {\mathrm{CaC}}_2{\mathrm{O}}_4(s)$$This equation excludes sodium and chloride ions because they are unaltered in the reaction.Understanding spectator ions is important because it helps simplify chemical reactions to focus on the changes that directly impact the formation of products. By removing unchanging ions, chemists can better understand the reactivity and stoichiometry of the essential parts of the reaction.

Insoluble Compounds

Insoluble compounds do not dissolve in solvents like water, often resulting in the formation of precipitates. These compounds are crucial in various fields of chemistry and practical applications. The concept of solubility is governed by molecular interactions and the thermodynamic properties of the compounds involved.An example is calcium oxalate ${\mathrm{CaC}}_2{\mathrm{O}}_4$, a compound resulting from the reaction between oxalate ions and calcium ions. Due to its low solubility in water, calcium oxalate forms a solid precipitate when its constituent ions meet in solution.Several factors affect the solubility of compounds, including:

• Temperature: Generally, higher temperatures increase solubility for most substances.
• Presence of complexing agents: These can increase solubility by forming soluble complexes.
• Solvent: The choice of solvent impacts the extent to which a compound will dissolve.

Knowing which compounds are insoluble is essential in predicting the outcomes of chemical reactions, especially in analytical and preparative processes. This understanding is also vital in fields like pharmacology, where compound solubility affects drug delivery and efficacy.