Intro

• A solution: a homogeneous (alike, no visibly different parts) mixture of 2 or more substances

• Mixable substances: “miscible” ☞ can be mixed in any proportion

• Some mixtures appear to be solutions when they're not (eg dusty air, milk)

• Solutions can be solids (teeth filling, alloys), liquids (rubbing alcohol, hand sanitizer), or gases (air tanks, or just air in general)

• Solutions are homogeneous mixtures of a solute (which is the substance in a lesser quantity) and a solvent (which is the substance in a greater quantity)

• In a 5% alcohol Coors beer, the alcohol is the solute and water is the solvent - there is less alcohol (5%) thus making it the solute

• The relative quantity of solute in a solution determines whether it is deemed to be concentrated or dilute

Concentrated  ←–––––––––––→  Dilute

• When water is the solvent, the solution is called “aqueous”

• These are common solutions & have many applications in chemistry

• Many molecules & ionic compounds can dissolve in water

• Water is a unique solvent because of its structure and shape, which makes it very polar

• The polarity of water is what attracts it to ions (both positive and negative) and other polar molecules

• Ionic compounds dissociate in water & the ions become hydrated (surrounded by water molecules). Dissociation equation shows the solid breaking into ions

e.g.

NaCl (s) → Na⁺ (aq) + Cl⁻ (aq)

• Molecules that are polar will also be attracted to water

• They also become surrounded by water molecules when dissolving

• Atoms of oxygen & hydrogen are often present in very polar molecules

• Oil does not dissolve in water, because it is not polar

• Oil can, however, dissolve other solutes that aren't polar (eg turpentine)

• Polar & nonpolar compounds can mix, if there is a compound that is attracted to both

• These surfactants like soaps & detergents have both polar and nonpolar parts on the same molecule

• Therefore, the soap will be attracted to both the oily food and water, which helps in cleaning

Solubility and Saturation

• The solubility of a substance is the MAXIMUM amount that can dissolve in a given solvent (usually 100g water)

• When this maximum has been reached ☞ solution is said to be saturated

• Excess solute will sit at the bottom of the container, regardless of how much its stirred or how long it sits

• Unsaturated solutions have LESS than the max amount of solvent dissolved

• Supersaturated solutions are formed under conditions that allow more solute to dissolve than is usually possible at a given temperature

• The solubility of a compound changes with temperature

• Solids usually become more soluble in water at higher temperatures since the added heat helps to break more bonds

• Gas solubility usually decreases as temperature increases, due to the energy given off while dissolving the gas particles, since there are no bonds requiring energy to break

• Added pressure will increase the solubility of gases, but has very little effect on liquids & solids

You can determine the saturation concentration of a solution by using the solubility graph

• If above the line ☞ supersaturated solution

• If on the line ☞ saturated solution

• If below the line ☞ unsaturated solution

• When there is excess solute in a solution, it will form a solid called a precipitate

• You can also determine if a precipitate will form from a solubility curve

Go from original temperature to new temperature. The precipitate is the difference (subtract) between how much is dissolved and the saturation point at that temperature

Solution Concentrations

• Solution concentrations are usually quantified, in units of solute dissolved per units of solution

• The most common are moles of solute per litre of solution ☞ this is called MOLARITY ((capital) M)

  M = Moles of solute

       **Litres of solution**

• The concentration of a solution can be used just like any other conversion factor

(If you're given g, then you can use molar mass to get to moles)

• Very small concentrations are often expressed in ppm (parts per million) or ppb (parts per billion) using either mass or volume

• 10⁶ for ppm, 10⁹ for ppb

ppm (m/m) = Mass of solute   x 10⁶

                  **Mass of solution**

ppm (v/v) = Volume of solute       x 10⁶

                **Volume of solution**

ppb (m/v) =   Mass of solute         x 10⁹

               **Volume of solution**

• Note: you could use 10⁹ for ppb in any formula and 10⁶ for ppm

• Concentrations can also be expressed as percentages, by mass and/or volume of solute in a solution

Percentage (m/v) =    Mass of solute         x 100

                             **Volume of solution**

• Alloys are solid mixtures

• Their concentrations are often expressed as a percentage by mass

Percentage (m/m) =  Mass of solute  x 100

                                **Mass of solution**

Formulas

Molarity:      Molarity  =   Moles/Litres

Ppm/ppb (m/m):       Mass of solute     x 10⁶ for ppm OR x 10⁹ for ppb

                                Mass of solution

Ppm/ppb (v/v):       Volume of solute     x 10⁶ for ppm OR x 10⁹ for ppb

                           Volume of solution

Ppm/ppb (m/v):       Mass of solute     x 10⁶ for ppm OR x 10⁹ for ppb

                          Volume of solution

Dilution and Mixing Solutions

• Dilution = when more solvent is added to a solution which lowers the concentration

• The new concentration can be determined by using the formula: C₁V₁ = C₂V₂

• Adding solvent doesn't change the moles of the solute that's been dissolved

• Since the concentration multiplied by the volume is the moles of a solute, they will be equal before and after ⇒ Molarity is a representation of concentration, but the moles themselves aren't going to change

• You need to rearrange the formula to find what you're looking for to solve dilution problems

• If 2 solutions with the same solute & solvent are mixed they will dilute each other - the moles of a solute can be added together as they are both in the final mixture

• Mixing solutions formula:  C₁V₁ + C₂V₂ = C₃V₃

Acidic and Basic Solutions

• Acids = substances that ionize to produce H+ ions in solution

• Bases = substances that dissociate to produce OH- in solution

• H+ ions are protons

• The strength of acids is the result of how completely the acid donates protons to the solution, making hydronium ions, H₃O+

• The degree to which an acid ionizes can be expressed as a percentage

• Strong acids, like HCl and H₂SO₄ ionize 100%

• Weak acids,  like CH₃COOH & other organic acids have a much lower ionization percentage.

Find Ionization percentage:

% ionization =      [H⁺]       x 100

                         \[acid\]

• The square brackets represent concentration in a formula!

• The pH and pOH are a measure related to the concentration of H+ or OH- ions in solution

• Each increment on the scale is a 10x difference in concentration

Formulas related to pH & pOH

• pH = - log [H+]

• [H+] = 10 - pH

• pOH = - log [OH-]