Problem 31 - Chemistry

Question

A few drops of concentrated ammonia solution added to a calcium bicarbonate solution cause a white precipitate to form. Write a balanced equation for the reaction.

Step-by-Step Solution

Answer

The balanced chemical equation for the reaction is: 2NH3 + Ca(HCO3)2 -> 2NH4HCO3 + Ca(OH)2.

Step 1: Identify reactants and products

The initial reactants of this chemical reaction are concentrated ammonia (NH3) and calcium bicarbonate (Ca(HCO3)2). Ammonia reacts with calcium bicarbonate to form a white precipitate. Since the white precipitate in a reaction with ammonia usually represents formation of ammonium compounds, it's reasonable to assume that the white precipitate that forms as a result of this reaction is ammonium bicarbonate (NH4HCO3). Besides, the reaction condition suggests that some insoluble calcium compound forms as well, hence it could be calcium hydroxide (Ca(OH)2). Thus, the chemical reaction can be schematically represented as follows: NH3 + Ca(HCO3)2 -> NH4HCO3 + Ca(OH)2.

Step 2: Write an unbalanced chemical equation

Before proceeding to balancing, let's initially write the chemical equation with our reactants and products: NH3 + Ca(HCO3)2 -> NH4HCO3 + Ca(OH)2.

Step 3: Balance the chemical equation

In balancing this equation, it is important to note that each type of atom must be the same on both sides of the equation. Inspecting the reactants and products, it's clear that the equation is not yet balanced. To balance it, put '2' in front of NH3 and NH4HCO3. Now the equation is balanced: 2NH3 + Ca(HCO3)2 -> 2NH4HCO3 + Ca(OH)2

Key Concepts

Understanding Chemical Reactions

At the heart of chemistry lies the study of chemical reactions, which are processes where substances, called reactants, transform into new substances, known as products. A reaction can involve complex molecules or more simple substances, and can result in various effects such as color change, temperature change, or precipitation — which is the formation of a solid from a solution.

When calcium bicarbonate meets concentrated ammonia, a chemical reaction occurs, leading to the creation of a white precipitate. This observable change signifies that a new substance has formed, which is a classic indicator of a chemical reaction taking place. To visually represent this process, we write a chemical equation that must be balanced to reflect the conservation of mass, pointing out that atoms are neither created nor destroyed in the course of a chemical reaction.

Precipitation Reactions Demystified

Precipitation reactions are a type of chemical reaction where two solutions combine and form a solid, known as a precipitate. This solid is often insoluble in the reaction mixture and thus separates out, which can be used to remove unwanted ions from a solution, or in qualitative analysis to test for the presence of certain ions.

In the given exercise, the reaction between concentrated ammonia and calcium bicarbonate yields a solid precipitate, identified as ammonium bicarbonate and calcium hydroxide. The formation of this white precipitate is a key diagnostic feature and is central to understanding how ions combine to form new compounds. Precipitation reactions are not only important in academic exercises but also have practical applications in water treatment, medicine, and various industrial processes.

Stoichiometry: The Art of Balancing Equations

Stoichiometry is a branch of chemistry that involves quantifying relationships between reactants and products in a chemical reaction. In everyday language, it’s the recipe for a chemical process, dictating the precise amounts of all substances involved. The cornerstone of stoichiometry is the balanced chemical equation, which ensures that the number of atoms for each element is the same on both sides.

Balancing chemical equations, as seen in the given solution, follows the law of conservation of mass. Students often start by listing the number of atoms for each element before and after the reaction, then add coefficients to balance these numbers. In the ammonium-calcium reaction, adjusting the coefficients before ammonia and ammonium bicarbonate to '2' retains the balance between reactants and products, reflecting the stoichiometric relationship that must exist within a chemical equation.