TASC Chemistry Level 4 cheat sheet

Atomic number equals the number of protons; in a neutral atom it also equals the number of electrons, so mass number = protons + neutrons.

Main-group elements: the group number (IA–VIIIA) gives the number of valence electrons; the period number gives the number of occupied electron shells.

Moles n = m / M, where m is mass in grams and M is molar mass in g/mol; 1 mol contains 6.022 × 10²³ particles.

Molarity M = moles of solute ÷ liters of solution; dilution follows M₁V₁ = M₂V₂.

Ideal gas law PV = nRT with R = 0.08206 L·atm/(mol·K); temperature must be in kelvin (K = °C + 273).

Balance equations by changing coefficients only, never subscripts, until each element's atom count is equal on both sides.

pH = −log[H₃O⁺]; pH below 7 is acidic, 7 is neutral, above 7 is basic at 25 °C, and each unit is a tenfold change in [H₃O⁺].

Le Chatelier's principle: adding a reactant shifts the system right; increasing pressure shifts toward fewer gas moles; raising temperature favors the endothermic direction.

Oxidation is loss of electrons (oxidation number rises); reduction is gain of electrons (oxidation number falls).

Independent variable: the factor the experimenter deliberately changes; dependent variable: the factor measured in response.

A control group receives no treatment or a placebo and provides the baseline for judging the effect of the independent variable.

Significant figures: for multiplication and division keep the least number of significant figures; for addition and subtraction keep the least number of decimal places.

Percent error = |experimental − accepted| ÷ accepted × 100%; percent yield = actual yield ÷ theoretical yield × 100%.

Read a meniscus at eye level at the bottom of the curve for water, recording all certain digits plus one estimated digit.

Separation methods: filtration (insoluble solid from liquid), distillation (boiling-point difference), chromatography (differential attraction to a stationary phase).

Calorimetry: q = mcΔT, with c = 4.18 J/(g·°C) for water; q is positive when heat is absorbed and negative when released.

Titration: deliver a standard solution from a burette into a measured volume of analyte until the indicator changes color at the endpoint.

Safety rules: wear goggles, waft vapors toward the nose, add acid to water when diluting, and keep flames away from flammable solvents.

IUPAC naming: find the longest carbon chain, number to give the lowest locants, and use -ane, -ene, or -yne for single, double, and triple bonds.

State symbols: (s) solid, (l) liquid, (g) gas, (aq) dissolved in water; Δ or a temperature written above the arrow indicates heating.

A net ionic equation shows only the species that change; spectator ions appear identically on both sides and are cancelled.

Scientific notation writes a value as a × 10ⁿ with 1 ≤ |a| < 10; exponents add during multiplication and subtract during division.

SI units used in chemistry include mol (amount), L or m³ (volume), K (temperature), g/mol (molar mass), J (energy), and mol/L (concentration).

Graphs place the independent variable on the x-axis and the dependent variable on the y-axis, each labeled with quantity and unit, plus a line of best fit.

Lewis structures use dots for valence electrons; atoms share electron pairs until they reach an octet (a duet for hydrogen).

Report values with correct units and significant figures, for example 0.100 M rather than 0.1 M when three figures are justified.

Greenhouse gases such as CO₂, CH₄, N₂O, and water vapor absorb infrared radiation emitted by Earth, trapping heat in the atmosphere.

Catalytic converters oxidize CO and unburned hydrocarbons to CO₂ and reduce NOₓ to N₂ using platinum, palladium, and rhodium catalysts.

Complete combustion of a hydrocarbon yields CO₂ and H₂O; incomplete combustion also produces CO and soot (carbon).

Hard water contains dissolved Ca²⁺ and Mg²⁺ ions; it is softened by ion exchange or by precipitation of carbonates.

Acid rain has a pH below about 5.6 and forms mainly when SO₂ and NOₓ emissions react with water and oxygen in the air.

Galvanic (voltaic) cells convert chemical energy into electrical energy; electrolytic cells use electrical energy to drive nonspontaneous reactions.

Recycling aluminum requires about 95% less energy than producing the metal from bauxite ore by electrolysis.

Municipal water treatment typically includes coagulation and flocculation, sedimentation, filtration, and chlorination or UV disinfection.

Thermoplastics can be remelted and reshaped, whereas thermosets cure permanently and cannot be remelted.