Solutions

Mixtures Atoms can combine in one of two ways:  Chemical Reaction  Mixture Mixture:  Combination of at least two substances  Can be physically isolated (separation techniques)  No breaking of chemical bonds

Mixtures Heterogeneous mixture: Components can be distinguished Homogeneous mixture: Components cannot be distinguished Solutions are a type of homogeneous mixture. Examples of solutions:  Water  Air Components:  Solute: The one who dissolves in the “solvent” (e.g. Coffee)  Solvent: The one in which the “solute” dissolves (e.g. Milk)

Solutions Properties of solutions:  Solubility  Concentration  Electrical Conductivity  pH Aqueous solutions: Solutions in which Water acts as the solvent  The polarity of Water makes it possible to dissolve ionic compounds (e.g. Salt) or molecules with a certain polarity (Sugar).  Non-polar substances (e.g. oil) do not dissolve well in Water.

Solutions Solubility: Maximum amount of solute that can be dissolved in a certain volume of solvent. Solubility depends on:  Nature of solvent  Nature of solute  Temperature  Pressure

Solutions Concentration: Amount of solute in a given amount of solution. NormalLessMore

Solutions

Concentration ChangeEffect on Concentration Dilution (Add Solvent)Decreases Dissolution (Add Solute)Increases Evaporation (Reduce Solvent)Increases

Solutions

Electrical Conductivity  Pure water does not conduct electricity  Certain substances dissolved in water (solvent) are the ones responsible for electrical conductivity (Electrolytes)  Electrical conductivity of a given solution is a measure of its ability to allow an electrical current to flow through it  Nonelectrolytes: substances that dissolve but do not conduct electricity  Maximum amount of solute that can be dissolved in a certain volume of solvent Electrolytic solutions: Solutions that contain an electrolyte (application: batteries) Electrolytes play a key role in animal’s adaptation. Electrolytes are the reason why ocean and rivers are different. (some fish would not survive in fresh water whereas others thrive in a lake)

Solutions Electrolytic Dissociation: Separation of a dissolved compound (Electrolyte) into two ions of opposite charge. NaCl (s) + H 2 O Na + (aq) + Cl - (aq)  Physical change: No change of the nature of the solute.  The movement of the ions formed is what allows an electric current to flow.  Nonelectrolytes do not produce ions when dissolved. C 12 H 22 O 11 (s) + H 2 O C 12 H 22 O 11 (aq)

Solutions Strength of electrolytes: Degree to which the electrolyte dissolves into its ions. The higher the degree, the stronger the electrolyte. (See Fig 2.25 on page 56)  Light bulb produces a bright light. Strong electrolyte  Light bulb produces a dim light. Weak electrolyte  Light bulb does not light. Nonelectrolyte Strong electrolyte: NaCl (s) + H 2 O Na + (aq) + Cl - (aq) 100 molecules 100 ions100 ions Weak electrolyte: HF (l) + H 2 O H + (aq) + F - (aq) 100 molecules 10 ions10 ions Nonelectrolyte: C 12 H 22 O 11 (s + H 2 O C 12 H 22 O 11 (aq) 100 molecules

Solutions Types of electrolytes: 1-Acids  Fruit juices, soft drinks, gastric juices  Sour taste  Litmus paper turns Red  Acids release H + when dissolved in Water HF (l) + H 2 O H + (aq) + F - (aq) H 2 SO 4 (l) + H 2 O 2H + (aq) + SO 4 2- (aq) HI (l) + H 2 O H + (aq) + I - (aq)

Solutions Types of electrolytes: 2-Bases  Cleaning products, some heartburn medication  Bitter taste  Feel slippery (react with oil in skin forming a kind of soap)  Litmus paper turns Blue  Bases release OH - when dissolved in Water NaOH (s) + H 2 O Na + (aq) + OH - (aq) Mg(OH) 2 (s) + H 2 O Mg 2+ (aq) + 2OH - (aq) NH 4 OH (l) + H 2 O NH 4 + (aq) + OH - (aq)

Solutions Types of electrolytes: 3-Salts  Table salt, Human diet (enhance food taste)  Made of a metal ion and a non-metal ion  Not all salts dissolve in water  Humans need salts (ions: Mg 2+, Ca 2+ ) for daily diet  Plats need salts (ions) that they get from the fertilizers NaCl (s) + H 2 O Na + (aq) + Cl - (aq) CaCl 2 (s) + H 2 O Ca 2+ (aq) + 2Cl - (aq) AgNO 3 (s) + H 2 O Ag + (aq) + NO 3 - (aq)

Solutions pH  Property that distinguishes acidic, basic and neutral solutions  Can be measured in different ways (indicator, pH paper, pH meter)  pH scale: 0 – 14  pH < 7 (Acidic)  pH = 7 (Neutral)  pH > 7 (Basic) pH = - log c(H + )  Log makes differences of one unit, to be ten times different (more or less)  Example: A (pH 3), B(pH1), C(pH9), D(pH10),  Therefore A is 100 times less acidic than B  And D is 10 times more basic than C  See Table 2.30 for values of c(H + ) and pH values