AP Chemistry · Handsworth Secondary 2026–27
Unit 0 · Study Guide
Dr. Ras Mulinta
Chemistry 11 Refresher
Self-check before Day 1
A one-page map of the prerequisite skills AP Chemistry assumes on day one. This is a checklist, not a re-teach, if a line does not click, go back to that section of the Unit 0 notes package. Be honest with yourself here in September; it is far cheaper than discovering the gap in February.
Must be able to do
- A Count significant figures, apply the ×÷ rule and the +− rule, and write any number in scientific notation.
- B Convert any unit to any other by the factor-label method, cancelling units on the page.
- C Move between mass, moles and particles in either direction: n = m/M, N = n·N_A.
- D Percent composition → empirical formula → molecular formula, given a molar mass.
- E Write and balance a reaction, and name its type on sight.
- F Run a full stoichiometry calculation, identify the limiting reactant, and compute percent yield.
- G Molarity, dilution by c₁V₁ = c₂V₂, and ion concentrations from a dissociation equation.
- H Ground-state electron configurations of atoms and ions; explain the four periodic trends.
- I Lewis structure → electron domains → molecular shape → polarity.
- J Rearrange any of the course formulas, and read a slope with its units.
The big idea that ties it together
Units are the check. Almost every prerequisite skill above is really one habit: carry the units through every line of work, and let them tell you whether the setup is right. A number without a unit is not an answer, and a unit that does not cancel is a setup error you can catch before you ever reach for a calculator.
Traps that cost marks
Rounding too early: round once, at the end. Rounding intermediate values drifts the final digit and AP will mark it wrong.
Balancing by changing subscripts: changing H₂O to H₂O₂ is a different substance. Only coefficients may change.
Ignoring the subscript in ion concentrations: 0.100 M Na₂SO₄ is 0.200 M in Na⁺ not 0.100 M. Write the dissociation equation first, every time.
Picking the limiting reactant by mass: the smaller mass is not the limiting reactant. Convert to moles and divide by the coefficient.
Confusing a polar bond with a polar molecule: CO₂ has two polar bonds and is non-polar, because the geometry cancels them. Check the shape before you answer.
Removing d electrons before s: transition-metal cations lose the outer s electrons first. Fe³⁺ is [Ar]3d⁵.
Reporting a bare slope: a slope carries units, and in chemistry those units usually identify what the slope is.
Quick self-check (work them, then check against the paper key)
- How many significant figures in 0.0304, and in 4500.?
- Convert 2.5 g/cm³ to kg/m³.
- Moles in 44.0 g of CO₂ and how many molecules is that?
- Empirical formula of a compound 40.0% S, 60.0% O by mass.
- Balance: C₂H₆ + O₂ → CO₂ + H₂O
- 8.0 g of H₂ and 32.0 g of O₂ react to form water. Which is limiting?
- What volume of 6.0 M NaOH makes 250.0 mL of 0.50 M NaOH?
- Electron configuration of Cl⁻.
- Shape and polarity of CH₂O (carbon is the central atom).
- Solve c = n/V for n, then find n when c = 0.25 M and V = 40.0 mL.
If you want to go further
Work the paper Prerequisite Refresher handed out in class and mark it against the key at the back wall. Anything you miss twice, bring to me in the first two weeks, that is exactly what the early September classes are for.