Problem 36 - Chemistry Matter and Change

Question

Aqueous solutions of ammonium phosphate and sodium sulfate are mixed. No precipitate forms and no gas is produced.

Step-by-Step Solution

Answer

No chemical reaction occurs; the mixture remains a solution of ions without any visible change.

Step 1: Identify the chemical formulas

Determine the chemical formulas of the compounds involved. Ammonium phosphate is \( (NH_4)_3PO_4 \) and sodium sulfate is \( Na_2SO_4 \).

Step 2: Write the balanced chemical equation

Write the molecular equation showing the mixing of these solutions: \( (NH_4)_3PO_4 + Na_2SO_4 \rightarrow ? \).

Step 3: Consider possible chemical reactions

Assess the possibility of reacting ions: Ammonium ions (NH₄⁺), phosphate ions (PO₄³⁻), sodium ions (Na⁺), and sulfate ions (SO₄²⁻) do not form any new compounds that are insoluble in water.

Step 4: Assess precipitation potential

Examine solubility rules to check for precipitation. All resulting compounds (if any) formed will remain dissolved as their ions in the solution because both ammonium and sodium salts are soluble in water.

Step 5: Confirm no visible reaction

Conclude that since no precipitate forms and no gas is produced, the chemical equation for this mixture simply represents the ions in solution. Hence, no visible chemical reaction occurs.

Key Concepts

Aqueous Solutions

An aqueous solution is a solution in which the solvent is water. In chemistry, these solutions are quite common because water is known as the "universal solvent" due to its ability to dissolve a wide range of substances. When a solute dissolves in water, it breaks into its individual ions or molecules, depending on the substance, allowing them to interact with water molecules.

For instance, when ammonium phosphate ( (NH_4)_3PO_4 ) and sodium sulfate ( Na_2SO_4 ) are dissolved in water, they dissociate into their respective ions. This process is essential for understanding how ions interact and why no visible reaction occurs when certain solutions are mixed.

• The water molecules surround and separate the ions.
• The solute must be polar or ionic to dissolve in water.

Understanding the behavior of aqueous solutions helps predict how different substances will react or remain unchanged in a solution.

Solubility Rules

Solubility rules provide guidelines for predicting whether an ionic compound will dissolve in water. These rules help chemists understand and foresee whether a compound will remain in solution as ions or form a solid precipitate.

Basic solubility rules include:

• Most salts containing alkali metals (like sodium, potassium) and ammonium remain soluble.
• Compounds containing nitrate ( NO_3^- ), acetate ( CH_3COO^- ), and bicarbonate ( HCO_3^- ) ions are generally soluble.
• Chlorides, bromides, and iodides are usually soluble, with exceptions like silver chloride.

When we mix ammonium phosphate and sodium sulfate in aqueous solutions, these solubility rules help us quickly evaluate that no new insoluble compounds are formed. Thus, no precipitate is seen, and everything remains dissolved in the solution, confirming the absence of a visible chemical reaction.

Ionic Reactions

Ionic reactions occur when ions in aqueous solutions interact to form new products. This often includes the formation of precipitates, gases, or weak electrolytes like water. To predict these reactions, chemists write ionic equations separating soluble strong electrolytes into their constituent ions.

For example, the equation between ammonium phosphate and sodium sulfate does not result in a reaction. Since all ions remain in solution, and no new covalent compounds or insoluble salts form.

• Ammonium ions ( NH_4^+ ) and sodium ions ( Na^+ ) do not form insoluble compounds with sulfate ( SO_4^{2-} ) or phosphate ions ( PO_4^{3-} ).
• All resulting ions remain dissolved, showing no visible reaction.

This demonstrates how ionic reactions allow us to determine the behavior of substances in solution, and in this case, concludes with no significant observable changes in the solutions mixed.