Question

Trisodium phosphate (TSP) is an effective grease remover. Like many cleaners, TSP acts as a base in water. Write a balanced equation to account for this basic behavior.

Short answer

The balanced equation for the basic behavior of trisodium phosphate (TSP) in water is given by: \[ Na3PO4(s) + H2O(l) \rightarrow 3Na^{+}(aq) + HPO^{2-}_4(aq) + OH^{-}(aq) \]

Step-by-step solution

Write the formula for trisodium phosphate

Trisodium phosphate is a chemical compound with the formula Na3PO4.

Dissociation of trisodium phosphate in water

When trisodium phosphate dissolves in water, it dissociates into its ions. The dissociation equation can be written as: \[ Na3PO4(s) \rightarrow 3Na^{+}(aq) + PO^{3-}_4(aq) \]

Reacting with water to form hydroxide ions

By acting as a base, trisodium phosphate can accept protons (H+) from water molecules, resulting in the formation of hydroxide ions (OH-). The phosphate ion (PO4^3-) will accept a proton from water to form hydrogen phosphate (HPO4^2-) and hydroxide (OH-) ions. The balanced equation for this reaction is: \[ PO^{3-}_4(aq) + H2O(l) \rightarrow HPO^{2-}_4(aq) + OH^{-}(aq) \] Putting all the steps together, we have a complete balanced equation to account for the basic behavior of trisodium phosphate in water: \[ Na3PO4(s) + H2O(l) \rightarrow 3Na^{+}(aq) + HPO^{2-}_4(aq) + OH^{-}(aq) \]

Key concepts

Chemical Equation Balancing

Understanding chemical equations is crucial for comprehending various chemical processes. When we speak of balancing chemical equations, we refer to the practice of ensuring the conservation of mass, as required by the Law of Conservation of Mass. In other words, we make sure that the number of atoms for each element involved in a reaction is the same on the reactant side (left side) as it is on the product side (right side).

To illustrate, let's consider the reaction of trisodium phosphate (TSP) dissolving in water which forms sodium ions, hydrogen phosphate, and hydroxide ions. In a balanced chemical equation, the number of atoms of each element must be equal on both sides. For example, in the final balanced equation for TSP behaving as a base in water:
\[ Na3PO4(s) + H2O(l) \rightarrow 3Na^{+}(aq) + HPO^{2-}_4(aq) + OH^{-}(aq) \]
we notice that there are three sodium atoms on both sides, one phosphorus atom, and four oxygen atoms. It's also key to remember that balancing involves coefficients, not subscripts, indicating the number of molecules, formula units, or moles.

Base Dissociation in Water

Bases dissociate in water to yield hydroxide ions and other ions. The process is a cornerstone of acid-base chemistry and crucial in understanding how cleaning agents such as trisodium phosphate work. In a water solution, the dissociation of TSP can be represented as follows:
\[ Na3PO4(s) \rightarrow 3Na^{+}(aq) + PO^{3-}_4(aq) \]
The solid trisodium phosphate dissolves, leading to the formation of sodium ions and phosphate ions. This change allows TSP to interact with water molecules further.

Dissociation is a reversible reaction, but for strong bases like TSP, the reverse reaction is negligible, leading to almost complete dissociation in water. This is important because the strength of a base is often associated with its ability to dissociate completely in an aqueous solution and influence the pH.

Hydroxide Ion Formation

The presence of hydroxide ions is what generally characterizes a solution as basic. Bases increase the concentration of hydroxide ions when dissolved in water, impacting the pH and making the solution more alkaline. In the case of TSP, hydroxide ions form when the dissociated phosphate ion reacts with water:
\[ PO^{3-}_4(aq) + H2O(l) \rightarrow HPO^{2-}_4(aq) + OH^{-}(aq) \]
The reaction involves the phosphate ion accepting a proton from the water molecule, thus producing a hydrogen phosphate ion and a hydroxide ion. It is this generation of hydroxide ions that gives TSP its cleaning power, as it enables the substance to act as a base and thereby emulsify greases and remove stains.

Being able to identify the formation of hydroxide ions in chemical reactions is fundamental for students to understand the concept of basicity and the properties that make substances like TSP effective in practical applications such as cleaning.