Question

Challenge Aqueous potassium iodide reacts with lead nitrate in solution, forming solid lead iodide.

Short answer

The balanced chemical equation for the reaction between aqueous potassium iodide (KI) and lead nitrate [Pb(NO3)2] forming solid lead iodide (PbI2) is: \(2 KI\ (aq) + Pb(NO_3)_2\ (aq) \rightarrow PbI_2\ (s) + 2 KNO_3\ (aq)\)

Step-by-step solution

Write the unbalanced chemical equation

First, let's write down the unbalanced chemical equation based on the information provided. The reactants are aqueous potassium iodide (KI) and lead nitrate [Pb(NO3)2]. The product formed is solid lead iodide (PbI2). The unbalanced chemical equation is as follows: KI (aq) + Pb(NO3)2 (aq) → PbI2 (s)

Determine the number of atoms for each element on both sides

Count the number of atoms of each element on both sides of the equation: Left side (Reactants): - K: 1 - I: 1 - Pb: 1 - N: 2 - O: 6 Right side (Products): - Pb: 1 - I: 2

Balance the chemical equation

We need to balance the equation by adjusting the coefficients in front of the chemical formulas, so that the number of atoms for each element is the same on both sides. First, we balance iodine (I) atoms: 2 KI (aq) + Pb(NO3)2 (aq) → PbI2 (s) Now, the number of I atoms on both sides is equal (2). Check the other elements: Left side (Reactants): - K: 2 - I: 2 - Pb: 1 - N: 2 - O: 6 Right side (Products): - Pb: 1 - I: 2 Now all the elements are balanced except for potassium (K). Since no other substance in this reaction contains potassium, we need to find a product that contains potassium. In the reaction, potassium (K) and nitrate (NO3) ions are also present in the solution but do not participate directly in forming the solid product. They are spectator ions, and their combination forms the remaining product, which is aqueous potassium nitrate (KNO3). The balanced chemical equation is: 2 KI (aq) + Pb(NO3)2 (aq) → PbI2 (s) + 2 KNO3 (aq) Now we have a balanced equation: Left side (Reactants): - K: 2 - I: 2 - Pb: 1 - N: 2 - O: 6 Right side (Products): - Pb: 1 - I: 2 - K: 2 - N: 2 - O: 6 The chemical equation is now balanced.

Key concepts

Balancing Chemical Equations

Balancing chemical equations is like ensuring both sides of a seesaw have equal weight. In a chemical equation, the reactants are substances you start with, and the products are what you end up with, after the reaction occurs. The goal is to ensure that the number of atoms for each element is the same on both the reactant and product sides of the equation. This maintains the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

To balance a chemical equation, start by writing out the unbalanced equation using the correct chemical formulas for each reactant and product. Next, tally up the number of each type of atom on both sides. Identify elements that appear in more than one reactant or product and balance them first where possible. Typically, it's easiest to begin by balancing elements that appear in only one reactant and one product.

You achieve balance by adjusting the coefficients, which are the large numbers you place in front of the chemical formulas in the equation. It's crucial to change only the coefficients, never the subscripts within the chemical formulas, because changing subscripts would change the compounds themselves.

Precipitation Reactions

Precipitation reactions are fascinating chemical processes where two solutions mix and an insoluble solid forms. This solid is called a precipitate. In the given reaction, aqueous potassium iodide and lead nitrate solutions combine to form solid lead iodide and aqueous potassium nitrate.

Here's how it works:

• The reactants are both aqueous, meaning they are dissolved in water.
• When these solutions mix, ions from each reactant meet. If they form a compound that doesn't dissolve well in water, that compound precipitates out of the solution as a solid.
• For the lead iodide reaction, Pb(NO3)_2 supplies lead ions (Pb^{2+}), and KI supplies iodide ions (I^-). Together, they form the insoluble PbI_2.

Precipitation reactions are crucial in various industrial processes and can also help in environmental applications like removing pollutants from water.

Stoichiometry

Stoichiometry is the study of the quantitative relationships in chemical reactions. It allows us to predict the amounts of products and reactants involved in a chemical reaction based on the balanced equation.

Understanding stoichiometry begins with the balanced chemical equation, where coefficients indicate the ratio of molecules or moles. Using this information, you can convert between different units, such as grams, moles, or liters, for the reactants and products.

For example, in the balanced reaction of 2 KI + Pb(NO3)2 → PbI2 + 2 KNO3, we can infer the stoichiometric relationships. Two moles of KI react with one mole of Pb(NO3)2 to produce one mole of PbI2 and two moles of KNO3. If you were given 10 grams of KI, you could use stoichiometry to determine how much PbI2 will form or how much Pb(NO3)2 is needed by converting grams to moles, using molar masses, then applying the mole ratios from the equation.

Stoichiometry is essential not only for experimental chemistry but also for industrial applications, where correct proportions are crucial for efficient production. It helps ensure that resources are used optimally and environmentally in chemical processes.

Spectator Ions

In many chemical reactions, particularly those in solution, some ions do not participate in the actual chemical change and remain unchanged in solution. These are known as spectator ions. They are present on both the reactant and product sides of the equation in the same form.

For the reaction involving KI and Pb(NO3)2, potassium ions (K^+) and nitrate ions (NO3^-) continue to exist in the solution even after lead iodide has precipitated. They do not form a new substance with other ions. In the balanced equation, you notice that potassium and nitrate ions appear on both sides and do not change states or bonding partners.

Spectator ions can be "cancelled" from the total ionic equation to form the net ionic equation, which is a simplified version that only shows the ions and molecules directly involved in the chemical reaction. Understanding spectator ions is important for simplifying complex reactions and focusing on the chemistry that affects the outcome of the reaction.