General Chemistry PHARM-101: Stoichiometry Quiz

General Chemistry for Pharmaceutical Sciences (PHARM-101)

• Course presented by Dr. Azza H. Rageh, Associate Professor of Pharmaceutical Analytical Chemistry at Taibah University
• Course covers Stoichiometry, Solution Concentration, and Chemical Reactions.

Stoichiometry

• Stoichiometry involves calculating the amounts of reactants and products in a chemical reaction
• It allows predicting product amounts based on reactant amounts
• It determines the necessary reactants to create a specific amount of product.
• Coefficients in balanced chemical equations represent relative mole amounts of substances.

Reaction Stoichiometry

• Example: 2 C₈H₁₈(l) + 25 O₂(g) → 16 CO₂(g) + 18 H₂O(g)
  • 2 moles of C₈H₁₈ react with 25 moles of O₂ to form 16 moles of CO₂ and 18 moles of H₂O.
• This example demonstrates the stoichiometric ratio between reactants and products. Stoichiometric ratios are used to calculate product amounts (or needed quantities of reactants).

Concentration of Solutions

• Concentration measures the amount of solute in a solution
• Units for concentration include percentage by weight, percentage by volume, parts per million, parts per billion, molarity, formality, normality and molality.
• Molarity (M) is a measure of concentration.
  • Molarity (M) = moles of solute / liters of solution

Molarity Calculations

• Example 1: Find the molarity of a solution with 25.5 g KBr dissolved in 1.75 L of solution.

  • Molarity (M) = 0.122 M

• Example 2: Calculate the liters of 0.125 M NaOH solution containing 0.255 mol NaOH.

  • Liters (L) = 2.04 L

Types of Aqueous Solutions and Solubility

• Familiar examples include salt water (NaCl & H₂O) and sugar water (C₁₂H₂₂O₁₁ & H₂O).
• These solutions are homogeneous mixtures.
• Solids like salt and sugar dissolve in water because of attractive forces between solute and solvent particles.

Dissolving of Ionic Compounds

• Each ion in the compound is attracted to surrounding water molecules.
• The water molecules pull the ions away from the crystal

Dissolving of Molecular Compounds

• Molecules of the compound mix homogeneously with water molecules.

Electrolytes and Nonelectrolytes

• Electrolytes dissolve in water to form solutions that conduct electricity (ions formed).
• Nonelectrolytes do not form ions when dissolved in water.
  • Strong Electrolytes: completely ionize
  • Weak Electrolytes: partially ionize

Types of Chemical Reactions (A Summary)

• Synthesis, Decomposition, Single Replacement, Double Replacement

Basic Types of Chemical Reactions

• Synthesis: Two or more reactants combine to form one product. (A + B → AB)
• Decomposition: A complex substance breaks down into simpler substances. (AB → A + B)
• Replacement (Single): One element replaces another in a compound. (A + BC → AC + B)
• Replacement (Double): The cations and anions of two ionic compounds switch places. (AB + CD → AD + CB)

Chemical Reactions Between Ions

• Ions react through water formation, weak electrolytes, precipitates, gases, and complex ion formation

Formation of Water: Acid-Base Reactions

• Metal hydroxides (including ammonium hydroxide) react with acids to form water.
  • Example: NaOH + HCl → NaCl + H₂O

Formation of Weak Electrolytes

• A strong acid with a salt that contains the anion of a weak acid forms the weak acid.
• Example: HCl + CH₃COONa → NaCl + CH₃COOH (weak acid)

Formation of a Precipitate

• Precipitation occurs when the concentration of dissolved ions exceeds the solubility limit forming an insoluble salt in a solution. Precipitate is solid.
• Example: AgNO₃ + NaCl → AgCl_(s) + NaNO₃

Formation of Gas

• Formation of a gas results from the product being gaseous or the product decomposing to form gas.
• Example: 2H⁺ + S^2- → H₂S_(g) -Example: Acid forms unstable acids (H₂CO₃, H₂SO₃, H₂S₂O₃, HNO₂)

Formation of Complex Ions

• A complexation reaction involves a Lewis acid (metal) and a Lewis base (ligand).
• Ligands form coordinate bonds to the metal to form a complex.
• Example: Cu²⁺ + 4 NH₃ → [Cu(NH₃)₄]²⁺

Reactions Involving Oxidation-Reduction (Redox)

• Redox reactions involve electron transfer.
• Oxidation is a loss of electrons, reduction is a gain of electrons.
• Oxidation and reduction reactions must always occur together.
• Example: 2 Na(s) + Cl₂(g) → 2 NaCl(s)

Oxidizing and Reducing Agents

• Oxidizing agent (oxidant) causes oxidation, and is reduced itself.
• Reducing agent (reductant) causes reduction and is oxidized itself.
• Example: 2C₈H₁₈(l) + 25 O₂(g) → 16CO₂(g) + 18 H₂O(g)

Assessment Questions

• Various assessment questions are provided related to the topics covered, including identifying products of reactions, classifying reaction types, calculating oxidation numbers, identifying oxidizing and reducing agents, and defining chemical reactions.

Test your knowledge of stoichiometry as it applies to chemical reactions in the context of pharmaceutical sciences. This quiz covers the calculation of reactants and products, as well as the interpretation of balanced chemical equations. Prepare to apply your understanding of chemical relationships in practical scenarios.