Laboratory program

Skills

• • Reading a graduated cylinder at the bottom of the meniscus, at eye level.
• • Recording one estimated digit beyond the finest scale division.
• • Distinguishing accuracy (closeness to true value) from precision (reproducibility).
• • Calculating percent error: |experimental − accepted| / accepted × 100%.

Safety

• • Glassware breakage
• • Unfamiliar chemicals — read the SDS section of the manual

Common mistakes

• • Reporting a digital balance reading with fewer digits than the display shows.
• • Dropping units in the data table and losing points on the post-lab.
• • Estimating zero uncertainty digits on analog glassware.

Skills

• • Water displacement for irregular solids: V = V_final − V_initial.
• • d = m/V, with the answer's sig figs limited by the least precise measurement.
• • Identifying evidence of chemical change: gas evolution, color change, precipitate, heat/light.
• • Using density as a conversion factor between mass and volume.

Safety

• • Sharp metal samples
• • Spilled water on the work surface

Common mistakes

• • Trapping air bubbles under the solid, inflating the displaced volume.
• • Calling a color change automatically chemical without other evidence.

Skills

• • Balancing the equation before doing any calculation.
• • Converting mass → moles → moles → mass through the mole ratio.
• • Identifying the limiting reactant by comparing moles of product each reactant could form.
• • Percent yield = (actual / theoretical) × 100%.
• • Classifying reactions: synthesis, decomposition, single/double replacement, combustion.

Safety

• • Acids and bases — goggles and gloves required
• • Possible gas evolution: ventilate

Common mistakes

• • Using mass ratios instead of mole ratios.
• • Reporting >100% yield and not recognizing it means the product was still wet.

Skills

• • M = mol solute / L solution — volume of SOLUTION, not solvent.
• • Serial dilution with M₁V₁ = M₂V₂.
• • Correct technique: dissolve solid in some solvent, then dilute to the final mark.
• • Beer's law reasoning: color intensity tracks concentration.

Safety

• • Concentrated stock solutions — always add acid to water, never the reverse

Common mistakes

• • Adding the full volume of water to the solid instead of diluting to a final volume.
• • Forgetting to convert mL to L before using M = n/V.

Skills

• • Relating flame color to a characteristic wavelength for each metal ion.
• • E = hc/λ to convert an observed wavelength into photon energy.
• • Explaining emission as an electron relaxing from an excited state to a lower level.
• • Using spectra as a qualitative identification tool for unknowns.

Safety

• • Open flame — tie back hair, no loose sleeves
• • Never look directly at intense sources for long

Common mistakes

• • Failing to convert nm to m before applying E = hc/λ.
• • Contaminated loops carrying over the previous ion's color.

Skills

• • Drawing Lewis structures, then applying VSEPR to get electron and molecular geometry.
• • Determining net dipole by vector-summing bond dipoles.
• • Ranking substances by IMF strength: dispersion < dipole–dipole < hydrogen bonding < ion–dipole.
• • Predicting relative evaporation rate and boiling point from IMF strength.

Safety

• • Volatile organic solvents — ventilate well, keep away from flame

Common mistakes

• • Confusing electron geometry with molecular geometry when lone pairs are present.
• • Calling a molecule polar just because it has polar bonds (CO₂, CCl₄ are not).

Skills

• • Collecting gas over water and correcting for water vapor pressure: P_gas = P_total − P_H₂O.
• • Always converting temperature to Kelvin.
• • PV = nRT with R = 0.08206 L·atm/(mol·K) — match R's units to your measurements.
• • Gas stoichiometry linking volume of gas to mass of reactant.

Safety

• • Pressure buildup — never seal a reaction vessel producing gas

Common mistakes

• • Using °C in PV = nRT.
• • Skipping the water-vapor correction on gas collected over water.

Skills

• • q = mCΔT with ΔT = T_final − T_initial.
• • q_system = −q_surroundings; the sign tells you exothermic vs endothermic.
• • Determining a metal's specific heat capacity by transfer into water.
• • ΔH_rxn per mole = q_rxn / mol limiting reactant.

Safety

• • Hot water and hot metal — use tongs
• • Exothermic dissolutions can get hot fast

Common mistakes

• • Forgetting the negative sign when relating heat lost to heat gained.
• • Using the mass of the metal instead of the mass of the water in q = mCΔT for the water term.