1. Stoichiometry and balancing chemical equations: Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. Many students struggle with understanding the concept of balancing chemical equations and performing calculations based on stoichiometry. To prepare for this topic, students should: a. Review the basics of chemical reactions, including the law of conservation of mass. b. Practice balancing chemical equations by identifying the correct coefficients for each reactant and product. c. Understand the concept of mole ratios and how to use them in stoichiometric calculations. d. Work through practice problems involving mass-to-mass, mass-to-volume, and volume-to-volume stoichiometry.2. Acid-base chemistry and pH calculations: Acid-base chemistry is another area where students often struggle, particularly when it comes to understanding the concepts of pH, pOH, and the relationship between them. To prepare for this topic, students should: a. Review the definitions of acids and bases, as well as the concept of conjugate acid-base pairs. b. Understand the pH scale and how it relates to the concentration of hydrogen ions H+ and hydroxide ions OH- in a solution. c. Learn how to calculate pH, pOH, and the concentrations of H+ and OH- using logarithmic equations. d. Practice solving problems involving titrations, buffer solutions, and the Henderson-Hasselbalch equation.3. Thermodynamics and enthalpy: Thermodynamics is the study of energy changes in chemical reactions, and enthalpy is a measure of the heat absorbed or released during a reaction. Students often find these concepts challenging and struggle with related calculations. To prepare for this topic, students should: a. Review the laws of thermodynamics and the concepts of internal energy, heat, and work. b. Understand the difference between exothermic and endothermic reactions, and how to represent these changes using enthalpy diagrams. c. Learn how to calculate enthalpy changes using Hess's Law and standard enthalpies of formation. d. Practice solving problems involving calorimetry, heat capacity, and specific heat.In summary, to adequately prepare for these commonly missed topics, students should review the fundamental concepts, work through practice problems, and seek additional resources or assistance if needed. This will help them build a strong foundation in chemistry and improve their performance on exams.