Question

Mixing an aqueous solution of potassium nitrate with an aqueous solution of sodium chloride does not result in a chemical reaction. Why?

Short answer

Mixing an aqueous solution of potassium nitrate (KNO₃) with an aqueous solution of sodium chloride (NaCl) does not result in a chemical reaction because the possible new compounds formed, potassium chloride (KCl) and sodium nitrate (NaNO₃), are both soluble in water according to solubility rules. No precipitate is formed, indicating that no chemical reaction occurs between the two solutions.

Step-by-step solution

Identify the compounds and their states

The two aqueous solutions being mixed are potassium nitrate (KNO₃) and sodium chloride (NaCl). Both are soluble in water, and their respective ions are present in the solutions. Potassium nitrate dissociates into potassium ions (K⁺) and nitrate ions (NO₃⁻), while sodium chloride dissociates into sodium ions (Na⁺) and chloride ions (Cl⁻).

Understanding solubility rules

There are certain solubility rules that help predict whether a precipitate will form when two solutions are mixed. According to these rules, nitrates (NO₃⁻) and alkali metal ions (Na⁺, K⁺, etc.) are generally soluble in water. This information is important to determine if any new insoluble compounds are formed during the mixing process.

Predict possible new compounds

When we mix these two solutions, possible new compounds could be formed by exchanging the ions, which results in potassium chloride (KCl) and sodium nitrate (NaNO₃). We now need to check if these new compounds are soluble or not.

Check solubility of the possible new compounds

According to the solubility rules mentioned earlier, both potassium chloride (KCl) and sodium nitrate (NaNO₃) are soluble in water. KCl is soluble due to the presence of an alkali metal ion (K⁺), and NaNO₃ is soluble because it contains a nitrate ion (NO₃⁻).

Conclude why no chemical reaction occurs

Since the possible new compounds formed (KCl and NaNO₃) are also soluble in water, there is no precipitate formed when the two solutions are mixed. As no insoluble compound is formed, no chemical reaction takes place. Therefore, mixing these two aqueous solutions (potassium nitrate and sodium chloride) does not result in a chemical reaction.

Key concepts

Solubility Rules

Solubility rules are an essential set of guidelines in chemistry that help predict the outcome when different ionic compounds are mixed in solution. These rules help determine whether a compound will dissolve in water or form a solid precipitate.

• Most nitrates ( ext{NO}_3^{-}) and acetates ( ext{CH}_3 ext{COO}^{-}) are soluble in water.
• Alkali metal ions like sodium ( ext{Na}^+) and potassium ( ext{K}^+) are typically soluble.
• Chlorides ( ext{Cl}^-), bromides ( ext{Br}^-), and iodides ( ext{I}^-) are generally soluble, except when paired with silver ( ext{Ag}^+), lead ( ext{Pb}^{2+}), or mercury ( ext{Hg}^{2+}).

In the case of mixing potassium nitrate and sodium chloride, both compounds contain ions known to be soluble according to these rules, ensuring that they remain dissolved in the solution.

Chemical Reactions

A chemical reaction involves the transformation of one or more substances into new substances with different properties. For a reaction to occur, there must be a change in the chemical composition of the compounds involved. This typically involves new bonds being formed or existing bonds being broken.

In an aqueous solution, ions can be free to mix, but they will only react to form a precipitate, gas, or molecular compound if the new product has limited solubility or stability.

• Chemical reactions often result in observable changes, such as color change, temperature change, gas production, or formation of a precipitate.
• No such changes are observed in the mixture of potassium nitrate and sodium chloride, indicating no chemical reaction occurs.

Precipitation Formation

Precipitation formation occurs when two soluble ions in solution combine to form an insoluble compound. This results in the formation of a solid precipitate that settles out of the solution.

According to the solubility rules, precipitation happens when the product of ion exchange during a reaction forms a less soluble or insoluble compound in water.
In the case of potassium nitrate and sodium chloride, combining them results in the potential formation of potassium chloride and sodium nitrate, both of which are soluble.

• Thus, no precipitate is formed, reinforcing the conclusion that no chemical reaction takes place between the initial solutions.

Dissociation of Compounds

Dissociation in chemistry refers to the process where molecules or ionic compounds separate or split into smaller particles such as ions, atoms, or radicals, typically in a reversible manner.

When ionic compounds dissolve in water, they dissociate into their respective ions.

• For example, potassium nitrate ( ext{KNO}_3) dissociates into potassium ions ( ext{K}^+) and nitrate ions ( ext{NO}_3^-).
• Sodium chloride ( ext{NaCl}) dissociates into sodium ions ( ext{Na}^+) and chloride ions ( ext{Cl}^-).

Each ion remains free to move throughout the solution, but they do not form new insoluble products in the mixture, explaining why no reaction is observed.