Chem Lab 1A Final (Got 50/50) UCR

Experiment #1 & #2

density of water w/ pipet, buret, graduated cylinder

Density: mass/volume

Density depends on temperature

Volume often incre w/ temp

Measure volume & density of a solid by water displacement

Rydberg Equation

1/𝜆 = Rh(nₗ⁻² - nₕ⁻²)

𝑅h = 1.097E7 𝑚⁻¹

Energy/Wavelength/Frequency/Plancks Constant/Speed of Light Relationship

E = hv

C = 𝜆v

h = 6.626E−34 𝐽⋅𝑠

c = 3.00E8 m/s

Change of Energy Equation

ΔE = hv/𝜆 = 2.18E-18(nₗ⁻² - nₕ⁻²)

Lyman series

nₗ = 1, ultraviolet region

Blamer series

nₗ = 2, visible region

Paschen series

nₗ = 3, infrared region

Calibrating Spectroscope

w/ Helium to measure Hydrogens wavelength

Scale reading vs Wavelength

Flame Test

heat promote electrons to excited states → return → color

BaCl₂

CuCl₂

KCl

LiCl

NaCl

SrCl₂

Clean w/ HCl

Ionization energy

energy needed take an electron from most stable state to a state infinitely far from nucleus

Components of mixtures favor either

mobile (solvent) or stationary phase (paper)

Ratio to Front

Rf = distance component moved/distance solvent moved

Components that interact strongly with the mobile (liquid) phase

travel at a faster rate than components that interact more with stationary (paper) phase.

Chromatography Dyes & Solvent

Red, green, yellow, blue

0.1% NaCl solution

Chromatography Metal Ions & Solvent

Co²⁺ Ni²⁺ Cu²⁺ Unknown

acetone (C3H6O) & 6M HCl

Experiment #5

Draw Lewis Structure-Isomers

Calculate formal charges

Hybridization/Shape/Polarity/Stability of Molecules

Stability: stable-obeys octet

Solid Compound exposed to atmosphere

contain some water

Ionic Salts

have larger amounts of water bound to the crystal (cation of salt) called water of hydration

Dehydration Reaction

solid structure & color may change

Efflorescence

hydrate loses water to the atmosphere upon standing, the amount lost depends on humidity. High humidity, hydrate will lose less/none. Dry atmosphere, hydrate will lose more

Hygroscopic

absorb water from air/sources

Desiccant

hygroscopic used to dry liquids/gases

Deliquescence

take up so much water from the air they dissolve in the water absorbed

Organic Compounds/Carbohydrates

not hydrates, water is formed by decomposition of the compound. Are not reversible (caramel color)

The number of moles of water per mole of ionic compound is

an integer or multiple of ½

Hydrate

formula includes a number of water molecules, undergoing reversible dehydration, water soluble

PART A. Hygroscopicity, Deliquescence, and Efflorescence

Compounds

Na₂CO₃ ⋅10H₂O

KAl(SO₄)₂ ⋅12H₂O

CaCl₂

CoCl₂ ⋅ 6H₂O

Weight, wait 1 hour, weigh again/ Classify as deliquescent, hygroscopic, efflorescent, or neither

PART B. Percentage of Water in a Hydrate

Weight crucible + cover

Weight crucible + cover + unknown

Heat 10 mins

Weight crucible + cover + residue

Heat & weigh

Add water—water soluble?

PART C. Reversibility of Hydration

Heat CuSO₄ ⋅ 5H₂O till color change (deep blue → pale blue), add water (deep blue), heat (pale blue), let sit, doesn't reabsorb water

PART D. Identification of Hydrates

Compounds

NiCl₂

KCl

CaCO₃

BaCl₂

In test tubes, heat ea (Water?), add water (soluble)?

Types of Waves Low to High Energy

Radio Wave, Microwaves, IR, Visible (red, violet), UV, X-rays, Gamma-rays

Absorption in IR

vibrates

Absorptions in Microwave

rotate

Absorption in Visible/UV

electron move to higher energy levels

The color of a solution perceived by eyes is

the complement of the light/color absorbed by the solution

absorption spectrum

graph, amt of light absorbed (wavelength vs absorbance)

Fraction of Light Absorbed Depends on

Type of species, wavelength, concentration, length of light path

Intensity of Color

Concentration of the solution (higher concentration = more light absorbed)

Beers Law

A = 𝜖𝑏C

A = solution's absorbance,

𝐴 = log(Iₒ/I) = -log(T) = log(1/T) = -log(T%/100)

b = path length of solution (cm)

C = concentration of solution (mole/liter aka M)

𝜖 (epsilon) = Molar absorptivity of substance at the wavelength at which the measurement is made (L/mol-cm) (proportionality constant)

Compound, Concentration, Path Length are fixed

Absorbance vs Wavelength = Absorption spectrum of compound

Compound, Wavelength, Path Length fixed

A vs C, straight line thru origin

%T is ___ proportional to the absorbance and the concentration of the sample

indirectly

PART A. Absorption Spectrum of a Food Coloring Dye:

Blank—water, dye (yellow, red, blue)

PART B. Analysis of the Copper Content of a Penny

Weight penny 1981 or earlier

Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂(g) + 2H₂O

Prep Standard Solutions

- Blank of HNO₃

- Cu²⁺ solution

- 3 test tubes w/ different ratios of Cu²⁺ to HNO₃

- unknown

[Graph of molarity vs absorbance]

Equation of Dilution

M₂V₂ = M₁V₁

Linear

SN = 2, 0LP

SN = 5, 3LP

SN = 6, 4LP

180°

sp

Trigonal Planar

SN = 3, 0LP

120°

sp^2

Tetrahedral

SN = 4, 0LP

109.5°

sp^3

Trigonal Bipyramidal

SN = 5, 0LP

3 in equatorial

2 in axial

120° & 90°

sp^3d

Octahedral

SN = 6, 0LP

90°

sp^3d^2

Bend

SN = 3 w/ 1LP <120°

SN = 4 w/ 2LP <109.5°

Trigonal Pyramidal

SN = 4 w/ 1LP

<109.5°

Seesaw

SN = 5, 1LP in equatorial

<90° & <120° & 180°

Square Pyramidal

SN = 6, 1LP

<90°

Polarity

Nonpolar [0, 0.4]

Polar [0.5, 2]

Ionic (2, 999]