Question

Aqueous solutions of potassium iodide and silver nitrate are mixed, forming the precipitate silver iodide.

Short answer

The double displacement reaction between potassium iodide (KI) and silver nitrate (AgNO₃) can be represented by the balanced chemical equation: KI (aq) + AgNO₃ (aq) → AgI (s) + KNO₃ (aq). In this reaction, the cations and anions swap partners, resulting in the formation of a precipitate, silver iodide (AgI), which is insoluble in water, and a soluble compound, potassium nitrate (KNO₃), which remains dissolved in the solution.

Step-by-step solution

1. Identify the chemical reaction

Mixing aqueous solutions of potassium iodide (KI) and silver nitrate (AgNO₃) results in a double displacement reaction. In this type of reaction, the cations and anions of the reactants swap partners to form new compounds.

2. Write the unbalanced chemical equation

Following the double displacement reaction pattern, the equation for the reaction of potassium iodide with silver nitrate is: KI (aq) + AgNO₃ (aq) → AgI (s) + KNO₃ (aq)

3. Verify that only silver iodide forms a precipitate

According to the solubility rules, most ionic compounds that contain alkali metal cations, like potassium, are soluble. This means KNO₃ will be soluble. However, ionic compounds containing the iodide anion (I⁻) with a metal other than alkali metals or ammonium ion are mostly insoluble. This means AgI will form a precipitate.

4. Balance the chemical equation

Check for the number of atoms on each side of the equation. In this case, the equation is already balanced as per the Law of Conservation of Mass: 1 K, 1 I, 1 Ag, and 1 NO₃ on the left side; 1 K, 1 I, 1 Ag, and 1 NO₃ on the right side. So the balanced chemical equation is: KI (aq) + AgNO₃ (aq) → AgI (s) + KNO₃ (aq)

5. Discuss the formation of the precipitate

In this double displacement reaction, the cations and anions of the reactants exchanged partners. The silver ion (Ag⁺) reacts with the iodide ion (I⁻) to form an insoluble compound silver iodide (AgI). Its insolubility causes the solid to precipitate from the solution. The remaining ions – potassium ion (K⁺) and nitrate ion (NO₃⁻) – form a soluble compound, potassium nitrate (KNO₃), which stays dissolved in the solution. The balanced chemical equation and the formation of silver iodide precipitate as a result of the reaction between potassium iodide (KI) and silver nitrate (AgNO₃) are now understood.

Key concepts

Chemical Reactions

At the heart of chemistry lies the rich and transformative concept of a chemical reaction, a process in which substances known as reactants undergo changes to form new substances, called products. It's akin to a culinary recipe where ingredients are combined and cooked to create a delicious dish.

The reaction in our example involves aqueous solutions of potassium iodide and silver nitrate. Like chefs swapping ingredients, chemical reactions involve the rearrangement of atoms. Reactions can be simple, involving only a couple of reactants, or they can be complex with multiple participants and products. They're categorized into different types like synthesis, decomposition, single displacement, and double displacement reactions—the latter being the type we're focusing on in our respective exercise.

Precipitation Reaction

Imagine a cloud-heavy with moisture that eventually becomes too saturated, releasing rainfall—a similar concept can be applied when discussing a precipitation reaction. This is a type of chemical reaction where two soluble salts in aqueous solutions react to form one or more insoluble substances known as precipitates.

In our textbook example, the marriage between potassium iodide (KI) and silver nitrate (AgNO₃) result in silver iodide (AgI) as the precipitate. Think of it as a matchmaker suggesting a new partner for the ions; these new pairings can sometimes be incompatible in a watery environment, solidifying their relationship quite literally as a solid precipitate.

Balancing Chemical Equations

Just as in a seesaw where balance is key to a smooth ride, balancing a chemical equation ensures that the atoms in the reactants are equal to the atoms in the products, honoring the Law of Conservation of Mass. Writing a balanced equation is essential for accurately representing the chemical reaction.

For our exercise, balancing was straightforward as each element in the reactants was already equal to its counterpart in the products: one potassium (K), one iodide (I), one silver (Ag), and one nitrate (NO₃) on each side. This balance tells us that no atoms were lost or gained during the reaction, they just swapped dance partners in this molecular ballroom.

Solubility Rules

As if navigating a list of who gets along with whom at a fancy dinner party, solubility rules guide us through predicting whether a compound will dissolve in water – be soluble – or not. According to these rules, most compounds containing alkali metal ions and the ammonium ion are water-friendly and dissolve easily, much like guests who mingle at the party.

In contrast, compounds like our silver iodide (AgI), with certain ions like silver and halides other than fluoride, are more like the introverted guests who stand aside and eventually leave – in a chemical sense, forming solids that do not dissolve. This is why AgI precipitates in our equation, while potassium nitrate (KNO₃) dissolves and remains in the aqueous solution.