Solutions Chemistry Mrs. Nunez
Solution - homogeneous mixture Solute - substance being dissolved Solvent - present in greater amount
Solvation • the process of dissolving solute particles are surrounded by solvent particles First... solute particles are separated and pulled into solution Then...
- + - - + + acetic acid salt sugar Non- Electrolyte Weak Electrolyte Strong Electrolyte solute exists as ions and molecules solute exists as ions only solute exists as molecules only DISSOCIATION IONIZATION
Dissociation separation of an ionic solid into aqueous ions NaCl(s) Na+(aq) + Cl–(aq)
Ionization breaking apart of some polar molecules into aqueous ions HNO3(aq) + H2O(l) H3O+(aq) + NO3–(aq)
Molecular Solvation moleculesstay intact C6H12O6(s) C6H12O6(aq)
NONPOLAR NONPOLAR POLAR POLAR “Like Dissolves Like”
Soap/Detergent • polar “head” with long nonpolar “tail” • dissolves nonpolar grease in polar water C. Johannesson
UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form Solubility concentration
Solubility • maximum grams of solute that will dissolve in 100 g of solvent at a given temperature • varies with temp • based on a saturated soln • Factors determiningrate of solution... • stirring (agitation) • surface area the dissolving particles • temperature
C. Solubility • Solids are more soluble at... • high temperatures. • Gases are more soluble at... • low temperatures & • high pressures (Henry’s Law). • EX: nitrogen narcosis, the “bends,” soda C. Johannesson
Solubility • Solubility Curve • shows the dependence of solubility on temperature
Solids tend to dissolve best when: • They are heated • They are stirred • Crushed into smaller particles Gases tend to dissolve best when: • The solution is cold • The pressure is high
Liquids • Miscible means that two liquids can dissolve in each other • water and antifreeze • water and ethanol • Partially miscible- slightly • water and ether • Immiscible means they can’t • oil and vinegar
Gases in liquids... • Henry’s Law - says the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid • think of a bottle of soda pop, removing the lid releases pressure • Equation: S1 S2 P1 P2 Sample 16.1, page 477 =
Concentration • The amount of solute in a solution. • Describing Concentration • % by mass - medicated creams • % by volume - rubbing alcohol • ppm, ppb - water contaminants • molarity - used by chemists • molality- used by chemists
CONCENTRATED DILUTE Concentrated vs. Dilute Notice how dark the solutions appears. Notice how light the solution appears. Small amount of solute in a large amount of solvent. Lots of solute, in a small amount of solvent.
substance being dissolved total combined volume A. Molarity • Concentration of a solution.
Molarity 2M HCl What does this mean?
M = Molarity Calculations • Find the molarity of a 250 mL solution containing 10.0 g of NaF. 10.0 g 1 mol 41.99 g = 0.238 mol NaF 0.238 mol 0.25 L = 0.95MNaF
mass of solvent only 1 kg water = 1 L water B. Molality
Molality • Find the molality of a solution containing 75 g of MgCl2 in 250mL of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2
C. Dilution • Preparation of a desired solution by adding water to a concentrate. • Moles of solute remain the same.
Dilution • What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution? GIVEN: M1 = 15.8M V1 = ? M2 = 6.0M V2 = 250 mL WORK: M1 V1 = M2 V2 (15.8M)V1 = (6.0M)(250mL) V1 = 95 mL of 15.8M HNO3
500 mL of 1.54M NaCl 500 mLwater 500 mL volumetric flask 500 mL mark 45.0 gNaCl Preparing Solutions • 1.54mNaCl in 0.500 kg of water • mass 45.0 g of NaCl • add water until total volume is 500 mL • mass 45.0 g of NaCl • add 0.500 kg of water
95 mL of15.8M HNO3 250 mL mark water for safety Preparing Solutions • 250 mL of 6.0M HNO3by dilution • measure 95 mL of 15.8M HNO3 • combine with water until total volume is 250 mL • Safety: “Do as you oughtta, add the acid to the watta!”
Percent solutions can be expressed by a) volume or b) mass • Percent means parts per 100, so • Percent by volume: = Volume of solute x 100% Volume of solution • indicated %(v/v) • Sample Problem 16.5, page 485
Percent solutions • Another way to do mass percentage is as mass/mass: • Percent by mass: = Mass of solute(g) x 100% Mass of solution (g) • Indicated %(m/m)
ColligativeProperty • property that depends on the concentration of solute particles, not their identity
Types • Freezing Point Depression (tf) • f.p. of a solution is lower than f.p. of the pure solvent • Boiling Point Elevation (tb) • b.p. of a solution is higher than b.p. of the pure solvent • Vapor pressure lowering
Some particles in solution will IONIZE (or split), while others may not. - Page 488 Colligative Properties CaCl2 will have three particles in solution for each one particle it starts with. Glucose will only have one particle in solution for each one particle it starts with. NaCl will have two particles in solution for each one particle it starts with.
Boiling Point Elevation Solute particles weaken IMF in the solvent.
- Page 494 The addition of a solute would allow a LONGER temperature range, since freezing point is lowered and boiling point is elevated.
Applications • salting icy roads • making ice cream • antifreeze • cars (-64°C to 136°C)