Question

Precipitate Formation The addition of hydrochloric acid to beakers containing solutions of either sodium chloride (NaCl) or silver nitrate \((KNO _{3} )\) causes a white precipitate in one of the beakers. a. Which beaker contains a precipitate? b. What is the precipitate? c. Write a chemical equation showing the reaction. d. Classify the reaction.

Short answer

a. The beaker containing silver nitrate (AgNO3) solution forms the precipitate when hydrochloric acid (HCl) is added. b. The precipitate formed is silver chloride (AgCl), which is a white solid. c. The chemical equation for the reaction is: \(AgNO_3 (aq) + HCl (aq) \rightarrow AgCl (s) + HNO_3 (aq)\) d. The reaction is classified as a precipitation and double displacement (or metathesis) reaction.

Step-by-step solution

Identify the possible reactions

When hydrochloric acid (HCl) is added to a solution of sodium chloride (NaCl) or silver nitrate (AgNO3), it can form the following chemical reactions: 1. NaCl (aq) + HCl (aq) → NaCl (aq) + HCl (aq) 2. AgNO3 (aq) + HCl (aq) → AgCl (s) + HNO3 (aq)

Analyze the products of the reactions

The first reaction between sodium chloride and hydrochloric acid does not result in the formation of any new compounds. They remain as ions in the solution. Thus, no precipitate will be formed. In the second reaction between silver nitrate and hydrochloric acid, silver chloride (AgCl) is formed, which is a white solid. As this is a solid product that forms in the aqueous solution, it is a precipitate.

Answer the questions

a. Based on our analysis, the beaker containing silver nitrate (AgNO3) solution forms the precipitate when hydrochloric acid (HCl) is added. b. The precipitate formed is silver chloride (AgCl), which is a white solid. c. The chemical equation showing the reaction is: AgNO3 (aq) + HCl (aq) → AgCl (s) + HNO3 (aq)

Classify the reaction

The reaction between silver nitrate and hydrochloric acid can be classified as a precipitation reaction and also as a double displacement (or metathesis) reaction. In this type of reaction, the cations and anions of two compounds exchange places to form two new compounds. In this case, the cation of silver nitrate (Ag+) and the anion of hydrochloric acid (Cl-) swap places, forming silver chloride (AgCl) and nitric acid (HNO3).

Key concepts

Double Displacement Reactions

A staple in chemical reactions, double displacement reactions involve two compounds swapping partners to form two new chemical entities. Think of it as a molecular dance where each participant ends up with a new partner. To visualize a double displacement reaction, imagine two ionic compounds in solution: compound A comprising cations A+ and anions B-, and compound B with cations C+ and anions D-. When they react, A+ pairs up with D- and C+ with B-, leading to products AC and BD.

These reactions often occur in aqueous solutions and can result in the formation of a precipitate, a gas, or a weak electrolyte. Precipitate formation, as in our exercise involving silver nitrate and hydrochloric acid, is a prime example where the ion exchange leads to an insoluble salt, AgCl, that falls out of solution.

Chemical Equation Writing

Writing a chemical equation is akin to creating a recipe for a chemical reaction. It's essential for clear communication of what happens when substances interact chemically. The equation provides a blueprint, showing the reactants transforming into products, conserving mass and charge in the process.

Steps for Writing:

• Identify the reactants and products.
• Write their chemical formulas.
• Ensure the number of atoms for each element is balanced on both sides.
• Indicate the states of matter using (s) for solids, (l) for liquids, (aq) for aqueous solutions, and (g) for gases.
• Include physical conditions, such as temperature, if relevant.

Following these guidelines would yield the equation from our example: AgNO3 (aq) + HCl (aq) → AgCl (s) + HNO3 (aq).

Silver Chloride Formation

Silver chloride formation is a classic illustration of a precipitation reaction, manifesting as a white solid emerging from an otherwise clear solution. It's a consequence of the limited solubility of silver chloride in water. When solutions of silver nitrate and hydrochloric acid mix, silver ions (Ag+) find chloride ions (Cl-) and form a bond to become AgCl, the compound precipitating out.

Even without intricate apparatus, the identification of a precipitate is a clear indicator of chemical change. The insoluble nature of AgCl distinguishes it from many other salts, making it an excellent subject for experiments in chemical education to visually demonstrate precipitation reactions.