Chemistry Final

**Why are no two emission spectra for different elements ever the same?

** Because each element has a unique arrangement of electrons and energy levels

**Why does each salt have its own distinctive flame test color?

** Because different metal ions have unique electron transitions that emit characteristic wavelengths of light when excited.

**Volume of NaOH used in each trial

** Final buret reading − Initial buret reading.

**Molarity of the acid in each trial

** (Molarity of NaOH × Volume of NaOH) ÷ Volume of acid.

**Average molarity of the acid

** (Trial 1 molarity + Trial 2 molarity) ÷ 2.

**Relative average deviation

** (|Trial 1 − Avg| + |Trial 2 − Avg|) ÷ 2 ÷ Avg × 100%.

**What sorts of transitions give rise to emissions in the ultraviolet and infrared regions?

** UV: transitions ending at n=1; IR: transitions ending at higher n levels such as n=3 or more.

**How can you tell whether a chemical reaction has taken place when Cu(NO₃)₂ is added to Zn?

** A visible reaction like bubbling or solid formation occurs; Zn(s) + Cu(NO₃)₂(aq) → Zn(NO₃)₂(aq) + Cu(s).

**Energy of photon for electron transition from n=6 to n=3 in hydrogen

** ΔE = 2.18 × 10⁻¹⁸ × [(1/n₁²) − (1/n₂²)] J.

**Limiting reactant between Al and KOH

** Convert grams to moles and compare mole ratios from balanced equation.

**Mass of alum produced from aluminum

** Moles of Al × molar mass of alum (474.39 g/mol).

**Percent yield from actual and theoretical yield

** (Actual yield ÷ Theoretical yield) × 100%.

**In the recycling of aluminum experiment

what species is formed after KOH is added?

**What is the purpose of an ice-water bath in the alum experiment?

** To cool the solution and promote alum crystal formation.

**Purpose of washing alum crystals with cold ethanol-water mixture?

** To remove impurities without dissolving alum.

**What happens when a hydrate cools on a lab bench instead of a desiccator?

** It reabsorbs moisture from the air

**Purpose of lab setup and label the six apparatuses?

** To heat and collect gas; Labels: Ring stand

**Geometry around central atom in model a?

** Tetrahedral.

**Geometry around central atom in model b?

** Trigonal planar.

**Mass of water driven off from a hydrate sample

** Mass of hydrate − Mass of anhydrous residue.

**Percent water in hydrate

** (Mass of water ÷ Mass of hydrate) × 100%.

**Why determine heat capacity of a calorimeter?

** To account for the heat absorbed by the calorimeter so total heat is accurate.

**Density of an unknown liquid from pipetted volume and mass

** Density = (Mass of beaker + liquid − Mass of empty beaker) ÷ Volume.

**ΔH for neutralization of 50.0 mL of 1.0 M acid and base with ΔT = 3°C

** q = mcΔT; ΔH = −q ÷ moles of limiting reagent.

**Was the neutralization reaction exothermic or endothermic?

** Exothermic; temperature increased.

**Will heat released increase if 100.0 mL acid and base used instead of 50.0?

** Yes

**Will final temperature increase if 100.0 mL of acid and base are used?

** No

**Volume in graduated cylinder (image)

** Read from image to correct number of significant figures.

**Beer’s Law equation and definitions

** A = εbc; A = absorbance

**How to determine molar absorptivity from Beer’s Law plot?

** From the slope of absorbance vs. concentration graph.

**Label volumes in three beakers to correct sig figs (image)

** Based on each beaker’s precision (e.g.

**Combined volume from three beakers to correct sig figs

** Use value with lowest precision (e.g.

**Wavelength of photon for electron drop from n=5 to n=2 in hydrogen

** 1/λ = R(1/n₁² − 1/n₂²); λ = 1 ÷ result.