CH120 – Chemistry: Molecular
Science
CH130 – Chemistry: The World
of the Molecule
Dr. Stan Von Euw
School of Biological and Chemical Sciences
stanislas.voneuw@universityofgalway.ie
Timetable
Syllabus
P. Flowers et al., Chemistry 2e, OpenStax , 2019
• Chapter 4: Stoichiometry of Chemical Reactions
Course Outline
Understanding Chemical Reactions in Aqueous Media:
Acids, Bases, Redox Systems, Precipitation, Solubility, and Quantitative Analysis
Lecture 1: Introduction
Lecture 2: Chemical Compounds I / Chemical Compounds Classified by their Nature
Lecture 3: Chemical Compounds II / Chemical Compounds Classified by their Functions
Lecture 4: Dissolution Reactions
Lecture 5: Precipitation Reactions
Lecture 6: Acid-Base Reactions
Lecture 7: Redox Reactions I
Lecture 8: Redox Reactions II
Lecture 9: Stoichiometry and Reacting Masses in Chemical Equations
Lecture 10: Limiting Reactants and their Impact on Chemical Reactions
Lecture 5
Precipitation Reactions
Precipitation reactions reveal the hidden artistry of
chemistry, where dissolved ions unite to create solid,
crystalline wonders
What Are Precipitation Reactions? Lecture 5
• Definition: A precipitation reaction occurs when two aqueous solutions react to form an
insoluble solid, known as a precipitate, that separates from the solution.
o General Formula: AB(aq) + CD(aq) AD(s) + CB(aq)
Reactants are aqueous (dissolved in water), and at least one product is a solid precipitate.
o Example: Silver chloride precipitating in water: AgNO3(aq) + NaCl(aq) AgCl(s) + AgNO3(aq)
Here, AgCl is the precipitate (an insoluble solid).
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• How to Predict Precipitation Reactions:
1. Break it Down: Identify the ions in the reactants (e.g., Ag⁺, NO₃⁻, Na⁺, Cl⁻).
2. Mix & Match: Swap cations and anions to predict products.
3. Use Solubility Rules: Determine if a product is insoluble (forms a precipitate).
A Quick Reminder: Solubility Rules in Water Lecture 5
Salts of:
• Group I elements (Li+, Na+, K+, Cs+, Rb+) are soluble except for Li₃PO₄
• NH4+ are soluble.
• Nitrate ions (NO3-) are generally soluble.
• Cl-, Br- and I- are soluble. Exceptions: Ag+ and Pb2+
• Most sulphates (SO42-) are soluble. Exceptions: Ba2+, Ca2+, Pb2+ and Ag+
• Most hydroxide (OH-) salts are only slightly soluble. Exceptions: Li⁺, Na⁺& K⁺ and NH₄⁺
which are soluble.
• Most carbonates (CO32-) salts are insoluble. Exceptions: Group I and NH₄⁺
• Most phosphates (PO43-) salts are insoluble. Exceptions: Na⁺& K⁺ and NH₄⁺
Applications of Precipitation Reactions Lecture 5
1. Water Treatment
• Purpose: Removal of toxic heavy metals from wastewater.
• Example: Lead ions Pb2+ are precipitated as lead sulphate
• The insoluble precipitate (PbSO4) is filtered out.
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2. Medical Use
• Purpose: Barium sulphate (BaSO4) is used as a contrast agent for X-ray imaging of the digestive
system because it is insoluble and non-toxic.
• Example: Formation of barium sulphate:
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3. Chemical Analysis
• Purpose: Precipitation titrations are used to determine the concentration of specific ions (e.g.,
chloride ions) in a solution.
• Example: Determination of chloride ions using silver nitrate
• The formation of the white precipitate (AgCl) indicates the presence of chloride ions.
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4. Industrial Use
• Purpose: Precipitation reactions are key in the production of pigments for paints and coatings.
• Example: Formation of lead chromate (PbCrO4), a yellow pigment:
Three Different Ways to Write Chemical Equations Lecture 5
1. Molecular Equation
• Represents all reactants and products as neutral compounds.
• Example:
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2. Complete Ionic Equation
• Shows all soluble compounds as dissociated ions.
• Example:
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3. Net Ionic Equation
• Focuses on the ions that participate in forming the precipitate (removes
spectator ions).
• Example:
Precipitation of Calcium Carbonate Lecture 5
Question 5.
Session ID 106-327-992
Precipitation of Calcium Carbonate Lecture 5
Question 6.
Session ID 106-327-992
Precipitation of Calcium Carbonate Lecture 5
Question 7.
Session ID 106-327-992
Precipitation of Calcium Carbonate Lecture 5
Question 8.
Session ID 106-327-992
Precipitation of Calcium Carbonate Lecture 5
Question 9.
Session ID 106-327-992
Precipitation of Calcium Carbonate Lecture 5
Question 10.
Session ID 106-327-992
