Solutions and Concentrations

What is a solution?

A homogenous (uniform througout) mixture of 2 or more substances

What is a solvent? (2)

• Any substance that has other substances dissolved in it

• This is the substance present in the largest amount

What is a solute?

The smaller component dissolved in the solvent

What is a variable composition?

• Solutions have variable composition

• The ratio of components can change

What is fixed composition?

• Pure substances have fixed composition

• The ratio of components is constant

  • Components are always present in the same ratio

What does aqueous solution mean?

A solution that is dissolved in water (water is the solvent)

What does miscible mean?

Liquids that dissolve readily in each other in any proportion (they mix)

What does immiscible mean?

Liquids that do not dissolve readily into each other (they do not mix)

e.g. oil and water

What are alloys? (2)

• Solutions containing metals

• Adding and mixing another element with a metal changes its proporties

What is solubility of a solute?

The amount of solute that dissolves in a given quantity of solvent at a certain temperature

What is a saturated solution?

Formed when no more solute will dissolve in the solution, excess solute is (visibly) present

What is an unsaturated solution?

A solution that is not yet saturated, therefore, it can dissolve more solute.

What is the rate of dissolving?

How quickly a solute dissolves in a solvent

What are the 4 factors that affect the rate of dissolving?

temperature, agitation, particle size, and intermolecular forces

How does temperature affect the rate of dissolving? (2)

• The rate of dissolving is greater at higher temperatures in solid solutes

• At higher temperatures, the solvent molecules have greater kinetic energy and collide with the solute more frequently, increasing the rate of dissolving

How does agitation affect the rate of dissolving? (2)

• Agitating a mixture by stirring or shaking the container increases the rate of dissolving

• Agitation brings fresh solvent into contact with undissolved solutes

How does particle size affect the rate of dissolving? (2)

• Decreasing the size of the particles increase the rate of dissolving

• When a larger mass is broken into smaller masses it increases surface area and allowing the solute to have more contact with the solvent

How do intermolecular forces affect the rate of dissolving? (3)

• The force of attraction between the solvent and solute plays a role

• When the force of attraction between different particles in a mixture is stronger than the force of attraction between like particles a solution is formed

• The strength of each attraction influences solubility

Explain Ion-dipole attractions (3)

• Ion-dipole attraction is the force of attraction between an ion and a polar molecule

• Ionic crystals consist of a repeating pattern of oppositely charged ions

• When an ionic compound is submerged in water (polar), the negative end of the dipole on some of the water molecules is attracted to the cations on the surface of the ionic crystal (and vice versa)

• If the ion-dipole attraction can replace the ionic bond between the cations and anions, the ionic compound will dissolve

• However, compounds with strong ionic bonds tend to be less soluble in water

What are electrolytes?

A solute with the ability to conduct electricity

Explain the solubility of covalent compounds (3)

• Most covalent compounds do not contain a negative and positive charge, thus they are insoluble in H₂O

• However, covalent compound that have polar bonds are extremely soluble and form hydrogen bonds with water

• But they are non-electrolytes

What are non-electrocytes?

Solutes that cannot conduct electricity since they remain neutral after dissolved

What are the 3 factors effecting solubility?

molecule size, temperature, and pressure

How does molecule size affect solubility?

Small molecules are more soluble then big molecules

How does temperature affect solubility? (5)

• Energy is needed to break the strong bonds between particles in the solid

  • At higher temperatures, more energy is present, and the solubility of most solids increases

• In liquids, the bond isnt as strong, thus the solubility is not greatly affected by temperature

• When a gas dissolves in a liquid, it loses some kinetic energy

  • At high temperatures, the dissolved gas gains energy again and comes out of the solution and is less soluble

How does pressure affect solubility? (2)

• Hardly affects solids and liquids

• The solubility of gases is directly proportional to the pressure above the liquid in which the gas is submerged inside

What is concentration?

The amount of solute quantity per solvent

Mass/ volume percent (m/v %)

m/v % = mass of solute (g)/ volume of solution (mL) x 100%

Mass/ mass percent (m/m%)

m/m% = mass of solute (g)/ mass of solution (g) x 100%

Volume/ volume percent (v/v%)

v/v% = volume of solute (mL)/ volume of solution (mL) x 100%

Parts per million (ppm) (2)

ppm = mass of solute/ mass of solution x 10⁶

mass of solute/ mass of solution = x g/ 10⁶ g of solution

Parts per billion (ppb) (2)

ppb = mass of solute/ mass of solution x 10⁹

mass of solute/ mass of solution = x g/ 10⁹ g of solution

Molar concentration (molarity) (3)

Molar concentration (molarity) is the number of moles of solute in 1 L of solution

Molar concentration = amount of solute (mol)/ volume of solution (L)

• C = n/v

What are dilutions? (5)

• Dilutions occur when there is more solute in a solution

• Be wary of the grammar in dilution questions!

• In a dilution, the moles of the solute are not changing, so:

• C₁V₁ = C₂V₂

• Do not use this equation in stoichiometry or titrations