Problem 41 - Chemistry Matter and Change

Question

Mixing hydrochloric acid (HCl) and aqueous calcium hydroxide produces water and aqueous calcium chloride.

Step-by-Step Solution

Answer

The balanced chemical equation for the reaction between hydrochloric acid (HCl) and aqueous calcium hydroxide is: \( 2HCl + Ca(OH)_2 \rightarrow 3H_2O + CaCl_2 \).

Step 1: Write the unbalanced chemical equation

The chemical equation for the reaction between hydrochloric acid and aqueous calcium hydroxide is: HCl + Ca(OH)₂ → H₂O + CaCl₂

Step 2: Balance the elements one by one

Start by balancing the chlorine (Cl) atoms. There are two Cl atoms on the product side, so add a 2 in front of the HCl in the reactant side: 2HCl + Ca(OH)₂ → H₂O + CaCl₂ Now, balance the hydrogen (H) atoms. There are 2 H atoms in each HCl molecule and 2 more H atoms in Ca(OH)₂ on the reactant side, giving a total of 2*2+2=6 H atoms. So, add a 3 in front of the H₂O on the product side: 2HCl + Ca(OH)₂ → 3H₂O + CaCl₂ Lastly, balance the oxygen (O) atoms. There are 2 O atoms in Ca(OH)₂ on the reactant side, so we have the correct number of O atoms on the product side: 2HCl + Ca(OH)₂ → 3H₂O + CaCl₂

Step 3: Verify if the chemical equation is balanced

Check if the number of atoms of each element is equal on both sides of the equation: - H atoms: 2 (in 2HCl) + 2 (in Ca(OH)₂) = 4 + 2 = 6 (in 3H₂O) - Cl atoms: 2 (in 2HCl) = 2 (in CaCl₂) - Ca atoms: 1 (in Ca(OH)₂) = 1 (in CaCl₂) - O atoms: 2 (in Ca(OH)₂) = 2*1 = 2 (in 3H₂O)

Step 4: Write the balanced chemical equation

Since the chemical equation is balanced, the final balanced equation is: 2HCl + Ca(OH)₂ → 3H₂O + CaCl₂

Key Concepts

Chemical Reactions

Chemical reactions are processes where reactants convert into products through breaking and forming of chemical bonds. Fundamental to understanding chemical reactions is recognizing that matter is neither created nor destroyed. Thus, a reaction must have the same number of each type of atom on both sides of the equation. This conservation of mass is what scientists refer to as the Law of Conservation of Mass.

For instance, in the reaction between hydrochloric acid (HCl) and aqueous calcium hydroxide (Ca(OH)₂), reactants undergo a transformation. They start as individual substances and, through the reaction, become water (H₂O) and aqueous calcium chloride (CaCl₂). The initial step in understanding this process is writing out the unbalanced chemical equation, which simply states the reactants and the products without regard to the number of atoms involved. The subsequent steps involve balancing each type of atom to match both sides of the equation.

Stoichiometry

Stoichiometry is the branch of chemistry that relates to measuring the quantitative relationships and making calculations based on the balanced chemical equations. The term stoichiometry derives from the Greek words 'stoicheion' (element) and 'metron' (measure), which quite literally means the measure of elements.

In practicing stoichiometry, we look at the coefficients of each substance in a balanced equation; these numerical values indicate the proportions of reactants and products involved in the reaction. For example, in a balanced equation like
\(2\text{HCl} + \text{Ca(OH)}_2 \rightarrow 3\text{H}_2\text{O} + \text{CaCl}_2\)
, the coefficients show us that for every 2 moles of hydrochloric acid and 1 mole of calcium hydroxide, the reaction produces 3 moles of water and 1 mole of calcium chloride. Understanding stoichiometry is vital for predicting the outcome of reactions and calculating the quantities needed for the reaction to occur.

Acid-Base Neutralization

Acid-base neutralization is a type of chemical reaction where an acid and a base, typically in aqueous solution, react together to produce water and a salt. This is an important concept in stoichiometry and chemistry due to its widespread applications including titrations, wastewater treatment, and the functioning of biological systems.

In the given exercise, hydrochloric acid (an acid) and aqueous calcium hydroxide (a base) react to carry out a neutralization reaction. The key to solving this type of equation is understanding that acids donate protons (H⁺ ions), while bases accept them to form water (H₂O). Salts, like calcium chloride in this case, are ionic compounds that result from the neutralization reaction. The balanced chemical equation for a neutralization reaction helps us to calculate how much acid is needed to neutralize a given amount of base or vice versa, and this is a common task in stoichiometry.