• solvation is the process of decomposition of a molecule due to its intermolecular interactions with other molecules
• solvent is any substance capable of solvation
• solute is any substance undergoing solvation
• solution is the mixture created by dissolving a solute in a solvent

Molecule movement in a solution

• molecules in a solution orient themselves so that the charged particles (or dipoles) attract one another
• polar solvents dissolve polar molecules
  • the molecules of solvent attack the molecules of solute and rip them appart forming micelle-like structures around the ions of the compound

Describing mixtures

Mass percent/fraction $w$

• it is the ratio of the mass of the solute to the mass of the solution

$$w=\cfrac{m_i}{m}$$

Molarity $c$

• molarity represents the number of moles of the solute in a volume of the solution
• it can be used to describe solutions which are hard to weigh
• it is prefered in most cases
• the base unit is $mol\cdot{dm^{-3}}$
  • it is usually written as just $M$

$$c=\cfrac{n_i}{V}$$

Molality $b$

• molality is the reation of the number of moles of the solute to the mass of the solvent
• it is widely used in biochemistry
• the base unit is $mol\cdot{kg^{-1}}$
  • is is usually written as just $m$

$$b=\cfrac{n_i}{m_s}$$

Concentrating/Diluting a solution

• mass percent equilibrium

$$m_{i1}=m_{i2}$$ $$w_1m_1=w_2m_2$$

• molarity/molality equilibrium

$$n_{i1}=n_{i2}$$ $$c_1V_1=c_2V_2$$ $$b_1m_{s1}=b_2m_{s2}$$

Dissociation and reaction schemes

• dissociation is a chemical reaction in which a molecule is broken up into its individual parts
• chemical reactions can be represented in rection schemes
  • rection scheme of a dissolution in water: $AB(s)\overset{H_2O}{\longrightarrow}Na^+(aq)+Cl^-(aq)$
  • the state of the compounds can be represented using letters in brackets behind the formula
    • $(s)$ - solid
    • $(l)$ - liquid
    • $(g)$ - gas
    • $(aq)$ - aqeous solution
  • the substance that causes the reaction to happen (reactant) is often placed above the arrow
  • the substance that is produced during the reaction but is unimportant for further continuation of the reaction is often placed under the arrow
• when no more substance can be disolved, we call it the point of saturation

Electrolytes

• electrolyte is a substance the solution in a polar solvent of which conducts electricity
  • oposite is nonelectrolyte
  • strong electrolyte dissolves fully and easily in a polar solvent
    • an example is sodium chloride $NaCl$
    • they are formed by strong acids and strong bases
    • dissolution of sodium chloride in water:
      $$NaCl(s)\overset{H_2O}{\longrightarrow}Na^+(aq)+Cl^-(aq)$$
  • weak electrolyte doesn’t dissolve properly or in its entirety in a polar solvent
    • an example is sodium fluoride $NaF$
    • they are formed by weak acid and strong base, strong acid and weak base or weak acid and weak base
    • they alter the pH of the solution
    • dissolution of sodium fluoride in water $$NaF(s)\overset{H_2O}{\longrightarrow}Na^+(aq)+HF(aq)+OH^-(aq)$$

Effects on solubility

• the amount of disolved salts rises with the rising temperature
  • the increasing temeprature weakens the bonds in the solute, thus making it more susceptable to dissolution
  • higher speeds of molecules of the solvent make it easier to break up crystal lattices
• the amount of disolved gas decreases with the rising temperature
  • the higher speed of the molecules of the solute make it easier to break from the attractive forces of the solvent

Separation methods

Evaporation

• a solution is heated up and the solvent is boiled of leaving the solute in a crystallizzed form
• should there be more solutes, the result will be the mix of them
• should the solute be thermically unstable, evaporation should not be used
• it is usually done under low pressure to lower the boiling point of the solvent

Crystallization

• a solvent is heated up and the solute is then added to the point of saturation; the mixture is left to cool and is left to cool down
• it is primarily used as a purification step
  • products can be very pure
• it is primarily used in organic chemistry to purify water soluble substances

Filtration

• a solution is passed through a porous barrier (filter) which removes any hard solids from a solution
• it is primarily used as a purification step, but can also be used as a separation technique
• permeate (filtrate) is the substances which goes through the filter (usually the goal)
• retenate (residue) is the substance which stays on the filter (usually the waste)

Chromatography

• it is a method of analysing a solution
• an absorber solid (stationary phase) with a sample (a drop of ink for example) is sunk into a solution (mobile phase)
• the solution will rise up due to the capillary action and the individual constituents will slow down based on their polarity
• the drop of ink will spread and show many colors as the different constituents stop at different places of the stationary phase

Distillation

• a solution is heated; as the liquids with different boiling points boil, they are liquified again in a condenser and seperated into a different conatiner
• if there are more liquids to be seperated, we call them fractions
  • the process is then called fractional distillation
    • it is primarily used in petrochemistry and making alcohol
• the vapor is liquified by cooling it down using cold water in most cases