Solutions

solutions (homogenous mixtures)

  • homogenous mixtures in which one substance is dissolved in another, but the articles are too small to be seen and do not settle out (dissolve)

  • ex. saltwater, sugar water

parts of a solution

  • solute: the component that is being dissolved (ex. the salt in salt water)

  • solvent: the component that does the dissolving (ex. water in salt water)

  • aqueous: water is the solvent of the solution

  • tincture: alcohol is the solvent of the solution

SOLVENT + SOLUTE = SOLUTION

solvation: the process of dissolving

  1. solute particles separate from surface of solid solute

  2. solvent molecules move apart so solute molecules can enter liquid

  3. solute molecules are attracted to the solvent molecules

  4. the keeps occurring until solute is completely dissolved in solvent

aqueous solution: a solution with water as the solvent

  • electrolytes are present in aqueous solutions

  • electrolytes dissociate completely into ions, they also conduct electricity (ex. HCl, MgCl2, and NaCl are strong electrolytes)

  • nonelectrolytes: compounds that dissolve in water but do not conduct electricity (ex. sugar, ethanol, ethylene glycol)

ionic compounds-compounds in aqueous solution

  • many reactions involve ionic compounds, esp reactions in water

  • dissociation: the separation of an ionic solid into aqueous ions (+/-) ex. NaCl(s) —> Na^+(aq) + Cl^- (aq)

covalent compounds

  • molecular compound solvation

  • dispersion: molecules stay intact. they do not separate (ex. C6H12O6 (s) —> C6H12O6 (aq)

solvation

  • “like dissolves like”

  • soluble: can dissolve in a liquid

  • insoluble: cannot dissolve in a liquid

  • two substances with similar intermolecular forces are likely to be soluble in each other

  • non-polar molecules are soluble in non-polar solvents (ex. CCL4 in C6H6)

  • polar molecules are soluble in polar solvents (ex. C2H5OH in H2O)

  • ionic compounds are more soluble in polar solvents (ex. NaCl in H2O or NH3)

  • (review): polar molecules have an unequal distribution of charges ex. H2O, NH3, etc.

  • (review): nonpolar molecules have an equal distribution of charges ex. O2, N2, CO2, etc.

solubility

  • solubility: the measure of how much a solute can be dissolved in each amount of solvent under certain conditions

  • factors that can affect solubility are:

  • the size of the solute crystals (surface area)

  • the pressure and duration of stirring

  • nature of solute and solvent

  • temperature

  • pressure

  • surface area

  • agitation

  • you can increase the rate of solution (how fast its dissolving) by:

  • stirring: increases the collisions between molecules

  • powder the solid solute: increases surface area

  • heat solution: makes particles move faster

solubility rules

  1. salts containing Group 1 elements are soluble (Li+, Na+, K+, Cs+, Rb+) salts containing the ammonium ion (NH4+) are also soluble

  2. salts containing nitrate ion (NO3-) are mainly soluble

  3. salts containing Cl-, Br-, I- are mainly soluble (important exceptions to this rule are salts of Ag+, Pb2+, and Hg2²+ so therefore AgCl, PbBr2, and Hg2Cl2 are all insoluble

  4. most silver salts are insoluble (AgNO3 and Ag(C2H3O2) are common soluble salts of silver; anything else is insoluble

  5. most sulfate salts are soluble (exceptions to this rule are BaSO4, PbSO4, Ag2SO4, and SrSO4)

  6. hydroxide salts of group 1 elements are soluble. hydroxide salts of group 2 elements (Ca, Sr, Ba) are slightly soluble

  7. hydroxide salts of transition metals and Al3+ are insoluble, therefore Fe(OH)3, Al(Oh3), and Co(OH)2 are not soluble

  8. most sulfides of transition metals plus Al3+ are insoluble but Fe(OH)3, Al(OH)3, and Co(OH)2 are not soluble

  9. carbonates are mainly insoluble. group 2 carbonates like Ca2+, Sr2+, and Ba2+ are insoluble (other insoluble carbonates are FeCO3 and PbCO3)

  10. chromates are mainly insoluble (ex. PbCrO4, BaCrO4)

  11. phosphates are mainly insoluble (ex. Ca3 (PO4)2, Ag3PO4)

  12. fluorides are mainly insoluble (ex. BaF2, MgF2, Pb21F2)

electrolytes vs nonelectrolytes

  • electrolyte: a substance that dissolves in water to give a solution that conducts electric current

  • nonelectrolyte: a substance that dissolves in water to give a solution that does not conduct an electric current

  • solutions of electrolytes can conduct electric current thus:

  • the positive ions and the negative ions disassociate (separate) in solution. the mobile ions (freely moving ions) can move a charge from one point in the solution to another point

  • solutions of nonelectrolytes cannot conduct electric current thus:

  • when a nonelectrolyte dissolves in water, there are no charged particles in the solution

  • solid ionic compounds cannot conduct electric current thus:

  • ions are present but they are not mobile

conductivity

  • ions must be present to conduct electricity and make the solution a good conductor therefore ionic compounds are good conductors

liquid solutions

  • miscible: two liquid that dissolve in each other (like dissolves like)

  • immiscible: two liquids that do not dissolve in each other (ex. water and oil)

solid solutions

  • alloys: a metallic substance created by combining two or more metals (ex. brass and bronze)

concentration of solutions

  • concentration: the amount of solute dissolved in a certain amount of solvent

  • concentrated: solute is present in a large amount relative to the solvent

  • diluted: solute is present in a small amount relative to the solvent

  • saturated: the point at which a solution can dissolve no more of the solute (no more solute dissolves)

  • unsaturated: a solution is still able to dissolve more of the solute (more solute dissolves)

  • supersaturated: a solution contains more of the solute than can be dissolved by the solvent in normal circumstances (becomes unstable, crystals form)

molarity

  • molarity (M): the number of moles of solute dissolved per liter of solution

  • the concentration of solutions — dilute vs. concentrated — depend upon molarity

molarity (M)= moles solute/liters of solution

OR

moles of solute = liters of solution (L) x molarity (M)

diluting solutions

  • dilution: adding solvent to the solution to decrease the concentration

  • the moles of solute before dilution stays the same amount of moles after dilution because the amount of solvent didnt change

  • moles of solute = molarity x volume of solution

  • M1 x V1 = M2 x V2

  • M1 x V1: initial solutions molarity and volume (aka stock or concentrated)

  • M2 x V2: final solutions molarity and volume (aka prepared of diluted)