Chem 107 Exam 1

What Actually Shows Up on Chem 107 Exam 1

The first midterm in General Chemistry is less about memorizing trends and more about translating between units, counting particles, and not losing points on sig figs. I watched a cohort lose roughly twelve collective points last semester on a single question where the answer was correct but the significant figures were wrong because someone rounded too early. That is the real shape of the exam. The exam typically covers the first five to seven weeks of material. You will see problems on unit conversions, dimensional analysis, atomic structure, isotope mass calculations, mole conversions, empirical and molecular formulas, and basic stoichiometry. Some instructors include solution concentration, but that lands more often on Exam 2. Know which chapters your professor actually tested in the last two years before you go deep into anything else. I prepared wrong for my first version of this course by re-reading the textbook chapters on quantum numbers instead of drilling stoichiometry and mole-mass conversions. The exam had zero quantum number questions and three stoichiometry problems that would have been passable if I had practiced them under time pressure. That mistake cost me a letter grade I did not get back.

The questions are usually a mix of multiple choice and short calculation problems. The multiple choice section tests conceptual traps, like whether density changes with sample size or which statement about isotopes is false. The calculation section demands clean setup work. Partial credit matters, and partial credit dies when your setup is unreadable.

How the problems actually work

Dimensional analysis is the engine for most of the exam. If you can set up a chain of conversion factors correctly, you can solve mass-to-mass stoichiometry, molarity dilutions, and gas law conversions without memorizing ten different formulas. Write the target unit on top, line up your fractions so unwanted units cancel, and check the cancellation before you touch a calculator. Mole conversions show up everywhere. Converting grams to molecules, liters of gas at STP to moles, or particles back to mass requires the same core relationships: Avogadro's number, molar mass, and the molar volume of an ideal gas at standard conditions. If your instructor uses 22.4 L/mol, memorize it. If they use a different reference state, adjust accordingly. A few professors switch to 24.5 L/mol for room temperature and pressure, and students who assume STP get it wrong every time. Isotope mass problems are where people slip. The weighted average formula is straightforward, but the trap is using the mass number instead of the exact isotopic mass when it is provided. Mass number is an integer approximation. Exact isotopic mass includes binding energy effects and is what the problem expects. I once saw someone use 35 and 37 for chlorine instead of 34.969 and 36.966, and the final answer drifted by about two percent. That is enough to miss the closest multiple choice option.

Sig figs are not optional. Your final answer must reflect the precision of the least precise measurement in the problem. If the question gives 2.5 g and 10.0 mL, your result should carry two significant figures, not three. Round only at the end. Rounding intermediate results compounds error and ruins otherwise correct setups. I keep a habit of writing one extra digit through every step and rounding on the final line. It takes two seconds and saves points.

A realistic edge case I ran into

During a practice run, I hit a stoichiometry problem where the balanced equation was not given and you had to write it from scratch. The reactants were an unknown metal carbonate and hydrochloric acid, and the products were a chloride salt, water, and carbon dioxide. I wrote the equation with the wrong stoichiometric ratio because I forgot that carbonate releases two moles of HCl per mole of CO2. The molar ratio between the metal carbonate and HCl is 1:2, not 1:1, and that difference propagated through every subsequent calculation. The workaround was to balance the equation before doing any math, then verify atom counts on both sides. Carbon, oxygen, hydrogen, chlorine, and the metal all had to balance. Once I caught the 1:2 ratio, the rest of the problem resolved cleanly. I learned to treat equation balancing as a hard gate, not a formality. If the equation is wrong, everything downstream is wrong, no matter how clean your arithmetic is.

What to prioritize and what to skip

Focus your study time on dimensional analysis, mole conversions, empirical and molecular formula determination, and stoichiometry with limiting reagents. These topics carry the most weight and appear in every version I have seen. Quantum numbers, electron configuration notation, and periodic trend predictions appear less often on Exam 1 and more on later exams. Nuclear chemistry equations are usually saved for the final. Check your syllabus and past exams to confirm the weighting for your specific instructor. Practice with untimed problems first, then shift to timed practice. The bottleneck on Chem 107 Exam 1 is rarely knowledge. It is speed and accuracy under pressure. When you have twenty minutes left and six problems remaining, you need your conversion chains to run automatically. Timed practice exposes which steps are slow and which assumptions you make carelessly.

A note on what this approach does not fix

Drilling problems will not compensate for weak algebra. If solving for an unknown in a multi-step equation feels uncomfortable, you will lose time and confidence. Basic rearrangement, fraction manipulation, and calculator use are prerequisites. There is no shortcut around that part. If your algebra is shaky, spend an evening on that first, then return to the chemistry problems. Similarly, this guidance assumes a standard General Chemistry sequence. If your course emphasizes thermochemistry, equilibrium, or kinetics on Exam 1, the scope shifts and the priorities change. Read your exam outline and adjust accordingly. No single strategy fits every syllabus.

Practical next steps

Get the practice problem set your instructor posted. Work through it once without notes, then review mistakes. Rewrite each failed problem from scratch until the setup runs cleanly. Track which topics still feel uncertain and drill those specifically. If you can set up and solve ten stoichiometry problems in twenty minutes without looking at examples, you are in a solid position for Chem 107 Exam 1. The exam rewards clean work, not fancy tricks. Write your setup clearly, track units through every step, respect significant figures, and balance equations before calculating. That is how people who know the material avoid losing points to carelessness rather than confusion.