Unit 3 Part 2

3.7 Solutions and Mixtures, 3.8 Representations of Solutions, 3.9 Separation of Solutions and Mixtures, 3.10 Solubility, 3.11 Spectroscopy and the Electromagnetic Spectrum, 3.12 Properties of Photons, 3.13 Beer-Lambert Law

solution

homogeneous mixture containing a solute and solvent

solute

what is being dissolved, substance there is less of

solvent

the dissolving agent (usually water), substance there is more of

how to make a solution

1. weigh solute, put it in volumetric flask

2. add solvent until the volume line

volumetric flask

precisely measures one volume

molarity

concentration of a solution, moles / liters

dilution

M₁V₁ = M₂V₂

how to dilute a solution

1. measure out solution using a buret (or graduated cylinder if there’s no buret)

2. pour solution into the volumetric flask

3. fill volumetric flask with water until you reach the line

how to find the concentration of an ion within a solution

apply a “mole ratio,” e.g. if there’s 2 OH^- within the compound, multiply the concentration by 2

what happens when you add an ionic compound to water

ionic compound dissociates into its ions, water surrounds cation with oxygen facing in, water surrounds anion with hydrogens facing in

miscible

liquids able to mix

immiscible

liquids cannot mix; one sits on top of the other

solubility product (K_sp)

indicates how soluble a substance is

higher K_sp means

substance is more soluble

what must occur thermodynamically for a solute to dissolve?

both the solute and solvent must break apart (endothermic), then the solute and solvent condense and mix together (exothermic)

what generally happens to the solubility when temperature increases?

increases

filtration

separates liquid and solid/precipitate

distillation

heat to separate solution by BP

evaporation

same as distillation but you don’t collect the solvent

fractional distillation

separate miscible liquids by BP

solvent extraction

separates immiscible liquids via a valve

chromatography

separates mixture by polarity

components of chromatography

stationary phase (paper/fixed component), mobile phase (solvent mixture)

Rf value

distance travelled by component / distance travelled by solvent, ratio showing how far the substances moved up the paper

column chromatography

collect parts of the solution/mixture

gas chromatography

turns sample into a gas and gives a read-out of the components

electromagnetic spectrum (from long to short wavelength)

radio, micro, infrared, visible, UV, x-ray, gamma

relationship between wavelength and frequency

inversely proportional

relationship between frequency and energy

directly proportional

relationship between wavelength and energy

inversely proportional

c

speed of light, 3 × 10⁸ m/s

λ

wavelength (in meters)

v

frequency (in Hz or s^-1)

h

planck’s constant, 6.626 × 10^-34 J*s

E

energy in joules

combined energy equation

E = hc/λ

UV/visible light

electron transitions

electron transitions

1. electron in ground state absorbs energy

2. electron jumps up to excited state - unstable

3. electron release energy as light and returns to ground state

radio waves

identifies position of atoms within a molecule

microwaves

identifies molecular rotations, determines IMFs

infrared waves

identifies molecular vibrations, determines functional groups

x-rays

identifies electron configuration (PES)

beer’s law

A = εbc

A

absorbance (no units)

ε

molar absorptivity coefficient (M^-1cm^-1)

b

pathlength (cm), assume 1

c

concentration (M)

photospectrometer

device that measures the absorbance of a solution

relationship of absorbance and concentration

direct

what happens if water droplets are left in the cuvette

absorbance will decrease

what happens if you don’t wipe the cuvette

absorbance will increase (fingerprints absorb more light)

what happens if the wavelength is set away from the absorption maximum (wavelength of optimal absorbance)

absorbance decreases

how to find the absorption maximum

on an absorbance vs. wavelength graph, highest point (peak)