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CHEM 112 Notes (1-13-16)
Clicker Question: Calculate the molarity of a 12.0% sulfuric acid solution (H2SO4; 98.08 g/mol) having a density of 1.080 g/mL.
12g H2SO4 (per 100g of solution)
98.08 ��/������= 0.122 ���������� ��2����4
100�� ���������������� ×1��
1.080 ����= 92.59���� = 0.09259��
Remember: Theory guides, but experiment decides
If you want to learn more check out Define homeostasis.
-Chemistry is an experimental science. Actually doing the experiment will yield more accurate solutions than theory
Principles of Solubility:
∙ Dynamic—able to change it
o Temperature can change the dynamic process
∙ Why this happens:
o Enthalpy (ΔH):
▪ Heat given off or absorbed (endothermic/exothermic)
▪ Usually a spontaneous reaction is exothermic and gives off heat, but some spontaneous solutions are endothermic
∙ Types of Interactions:
∙ The Solution Process:
o First need to undo solvent and solute (requires energy)
o Separation of solute and of solvent is endothermic
o Bringing the two together is exothermic
o See “Enthalpy of Solution” figure in lab manual
ΔHsolution = ΔH1st step + ΔH2nd step + ΔH3rd step
o 1st step:
▪ Absorbs energy to separate solute We also discuss several other topics like How did the atomic bomb affect society?
o 2nd step:
▪ Absorbs energy to separate solvent
o 3rd step:
▪ Releases energy to combine both
o Solid < Liquid < Gas (least spontaneity to most spontaneity)
∙ Spontaneity and Solubility:
o What causes a solute to be dissolved?
▪ Like dissolves like
∙ Intermolecular Forces:
▪ Polar molecules
o London Dispersion Forces
▪ Everything has it, but it’s the only force nonpolar
molecules have, so it’s typically associated with
o Hydrogen Bonding
▪ Molecule must be polar and have H-F, H-O, or H-N
▪ Strongest = covalent bonds
∙ All intermolecular forces are significantly
weaker than covalent bonds If you want to learn more check out Who is henry brackenridge?
▪ Weak = hydrogen bonds
▪ Very weak = dipole-dipole
▪ VERY very weak = London dispersion forces
∙ Relative Solubility:
o Ex: hexane and water
C C H H
▪ Won’t dissolve—not alike
∙ London dispersion forces holding hexane won’t break for water
∙ Water has hydrogen bonds
∙ Water is polar, and hexane is nonpolar
o Will iodine dissolve better in hexane or water?
I I If you want to learn more check out What is the first american constitution?
▪ Iodine has London dispersion forces, but no hydrogen bonds We also discuss several other topics like What is a major cell nutrient produced during photosynthesis, a raw material for other molecules?
▪ Answer: Hexane We also discuss several other topics like Why do companies go into advertising their products?
o What about methanol (CH2OH)?
▪ Answer: H2O
o NOTE: If it’s not an ionic salt or doesn’t have hydrogen bonds, it won’t dissolve in water
∙ Why is water a universal solvent?
o For an ionic compound to dissolve, ions have to separate and solvent (water) has to separate
o Next step: hydration
▪ Water molecules separate ions
Ionic Compound Water
Ions Separate Water Separates
∙ Gas can be a solute
o Pressure will have a big impact in this case
o Henry’s Law:
▪ C = KD (directly proportional)
▪ C—concentration (could be molarity-M, molality-m, or partial pressure PA)
▪ K-value gets smaller as temperature increases
▪ As temperature increases, solubility increases (trend)
o Example of Henry’s Law worked out:
∙ H2O at 20°C
∙ Partial pressure = 8.00 torr
∙ K = 3.91 x 10-2 molal/atm
∙ 1atm = 760torr
o ���� =8.0�������� ×1������
∙ �� = 3.91 × 10−2 ����������
∙ �� = 4.12 × 10−4����������
o A + B C + heat (exothermic—releases heat)
o A + B + heat C (endothermic—absorbs heat
▪ If you increase the temperature of an exothermic reaction (-ΔH), you’re adding more product, so it will go in the other direction to reach equilibrium
o ↑T of exothermic reaction (-ΔH)—equilibrium shifts to reactants (decreases solubility because you are shoving solute out of the solution)
o ↑T of endothermic reaction (ΔH)—equilibrium shifts to products (increase solubility because you are helping the solute dissolve)