Solution - a homogeneous mixture in which a solute (solid, liquid or gas) is dissolved in
a solvent (usually liquid)
- can be coloured or colourless but must be clear/transparent
Aqueous - dissolved in water, i.e., water is the solvent Solute - a substance dissolved in another substance ex Sugar :
-Solvent - a substance capable of dissolving another substance ex: water
Water
- called the universal solvent because it dissolves many solutes
- this is due to: 1. Its abundance and availability
2. I's Polarity- one end is s1.ghtly Positive, and the other end is slightly negative
Dissolving - Separation or a solute in a Solvent
Methods of Dissolving
1. lonic Dissociation only ionic compounds
Á physical process by which the ions in an ionic compound separate, becoming individual ions.
The negative end of water (O) surrounds the positive ions and the positive end of water (H) surrounds the negative ions.
Na.OH(5) + H2
(1)
hydrated /aqueous ions
Hydration - the process in which ions are surrounded by water molecules
The water stabilizes the ions in Solution, Preventing thiem from attracting each other
sodium chloride → sodium cations + chloride anions
When a sodium chloride crystal is placed in water, water molecules are attracted to the sodium cations and chloride anions. These attractions pull the ions away from the crystal. Once in
solution, each ion is surrounded by a layer of water molecules in a process called hydration. .
2. Molecular Dissociation (simple dissolving)
A physical process in which a molecular solute is separated by a solvent to produce molecules in a different phase.
3. Covalent lonization
A chemical process by which molecules react with a solvent to produce free, mobile ions. Only occurs with acids and ammonia
Rate of Dissolving and Solubility
Rate of dissolving is defined as how quickly a solute dissolves in a solvent. It depends on several factors, i.e., temperature, agitation and particle size.
1. Temperature - As temperature increases, rate of dissolving increases energy
- Rise in temperature causes energy of particles to increase-causing particles to collide more
2. Agitation - Shaking, Sirring, mixing
* causes more
Collisions
- This increases rate of dissolving because :t bringo Particles into contact more often to Increasing collisions
3.- Surface Area: -Surface- Area increases rate of dissoluing.
(SA)
- This is because the number of solute particles in direct contact With solvent increases
example: reaction between magnesium metal and hydrochloric acid
Solubility is always temperature dependant
Solubility and Particle Attractions
Solubility is the maximum amount of solute that can dissolve in a fixed amount of solvent at a constant temperature.
Solutes dissolve in solvents of similar polarity.
*LIKE DISSOLVES LIKE*
* Polar Solutes dissolve in polar solvents
* Non-Polar Solutes dissolve in non-Polar Solvents.
Solubility is also affected by pressure and temperature.
Temperature:
The solubility of a substance is different at different temperatures.
Solids: solubility increases with increasing temperature
The greater kinetic energy of the molecules leads to more collisions, which helps the solute dissolve faster..
Liquids: solubility is not affected by temperature
Gases: the solubility of gases decreases with an increase in temperature
Gas particles have lots of kinetic energy and by increasing temperature, the particles gain even more energy and can escape from the solution.
Pressure:
Changes in pressure only affect gases in solution. Solids and liquids are unaffected.
Gases: increasing pressure, increases the solubility of a gas in liquid Gas particles collide more frequently and react at a faster rate.
Miscible - liquids that dissolve in each other ex: ethanol and water (Polar)
Immiscible - ligoids that dont dissolue in eachother
ex:ol and Water
个
non-polar
个
Polar
Solubility Graphs
- a graph that shows the relationship between the solubility of a solute and the temperature of the solvent
Each point along the curve represents the maximum amount of solute that will dissolve at that temperature. The solubility of a substance is different at different temperatures.
- Different Solutes behave differently. at different temperatures
- As temperature increases, the solubility of a gas decreases
Types of Solutions
Saturated Solutions - solution in which no more solute can be dissolved at a fixed
temperature
Unsaturated Solutions - Solution in Which more solute can be dissolved at a fixed temperature
Supersaturated Solutions - Solutions Which contain more dissolved solute
than is normally possible al a fixed temperature
- very unstable
- can Crystalize(out)
Hydrogen Bonding and Water
Hydrogen bonding accounts for many of the unique physical properties of water.
These properties are very significant for life on Earth.
Property
Physical or Biological Significance
high melting and boiling points
• permits water to exist as liguid at room temperature
• keeps body fluids liquid over a large range of temperatures
expansion when cooling from
4°C to 0°C
• causes ice to float
• causes water to freeze from the top down, allowing life to continue below it
high surface tension
• pulls water into round droplets
• allows small insects to "walk on water'
ability to exchange thermal energy with little change in temperature
• enables water to absorb a great deal of thermal energy for a small increase in temperature and to release a great deal of energy for a small decrease in temperature
• has a moderating effect on temperature
-changes in organisms and the environment
inability to mix with nopolar compounds
• enables organisms to retain water. because of waterproof coating
• allows organisms to store nopolar substances i.e., fats and oils
Intermolecular Forces - forces of attraction belween molecules
ex: diPole-diPole, hydrogen bonds, ion -diPole
Intramolecular Forces - forces of attraction between atoms or ions
ex: covalent bonds, ionic bonds
Types of Intermolecular Attractions
1. Dipole-Dipole Forces
The attraction between opposite charges on two polar molecules. These are weak attractions.
The oppositely charged ends of the polar molecules attract, whereas the similarly charged ends, repel.
2. Ion-Dipole Attractions
These are the attractive forces between an ion and a polar molecule. The negative end of the dipole attracts cations and the positive end of the dipole attracts anions.
Hydrogen Bonding
The attraction between hydrogen atoms bonded to N, O or F atoms on one molecule to a lone pair of electrons of an N, O or F atom on another molecule.
Hydrogen bonds are only one-tenth as strong as covalent bonds. They are, however, the strongest of the intermolecular bonds
Molar Concentration
Concentration = molarity
The amount or solute (in moles) Per volume or solution (in litres
Dilutions
Solutions have variable composition. This means that different ratios of solute to solvent are possible, i.e., concentrated or dilute.
Concentrated - high ratio of solute to solvent
Dilute - low ratio of solute to solvent
Dilution - the process of reducing the concentration of a solution, usually by adding
more solvent
- the amount of solute stays the same
concentrated solution
Dilution:
Solvent increases but the numbero solute stays the same.
Stock solution:
This is a solution of known concentration of which small amounts are used to make less concentrated solutions as needed. It is used in labs and schools as an efficient and cost effective method to make solutions that are safe. For example, hydrochloric acid comes as a 12mol/L stock solution. This is very dangerous. It is diluted for use.
C1V1 = C2V2
* Must be Same units
c,= Concentration of initial
V,= Volume of initial Solution
solution
C2= Concentraton of riew
V2=Volume or new solution
Percent Concentrations
- express ratios of solute to solution as a whole
- NOT ratios of solute to solvent
1. Concentration as a mass/volume percent (m/v%)
mass/volume percent - the mass of a solute dissolved in a volume of solution, expressed as a percent
e.g. 6%m/v - 6g of every 100mL of solution is solute
M/٧ / =
Mass or solute
× 100
Volume of solution
e.g. A pharmacist adds 2.0mL of water to 1.0g of powdered drug. The volume of the solution is 3.0mL. What is the m/v% of the solution?
Mv% =
1.0
3.0
× 100
= 33.3%
2. Concentration as a mass/mass percent (m/m%)
mass/mass percent - the mass of a solute dissolved in a mass of solution, expressed as a percent
e.g. 5%m/m - 5g of every 100g of solution is solute
mass of solde
m/m/. =
- x 100
mass or solotion
3. Concentration as a volume/volume percent (v/v%)
volume/volume percent - gives the volume of the solute dissolved in a volume of solution, expressed as a percent
- also referred to as the volume percent concentration or percent by volume
- e.g. rubbing alcohol
e.g. 50%v/v - 50mL of every 100mL of solution is solute
4. Concentration in parts per million (ppm), parts per billion (ppb) & parts per trillion (ppt)
ppm, ppb, ppt - describe the mass of solute present in a mass of solution
Solubility and Solubility Rules
Solubility - the maximum amount of solute that will dissolve in a given amount
of solvent at a specific temperature
Soluble - if more than 1.0g will dissolve in 100.0mL of solvent
Insoluble - if less than 0.1g of solute will dissolve in 100.0mL of solvent (W.l not dissolve)
Slightly soluble - if solubility is between 0.1g and 1.0 g per 100.0mL of solvent
Precipitate - an insoluble product formed from the reaction of two aqueous
substances
The solubility of ionic compounds is summarized in a table of solubility rules.
Solubility Rules
-summarize which combinations of positive and negative ions form insoluble compounds, i.e., predict the precipitate(s) in double displacement reactions
• To balance total ionic equatioris, all entities on one side, must be accounted for on the other side. Also, the net charge on both sides must be the same.
lons present on both sides of the equation can be cancelled out, resulting in a net ionic equation.
net ionic equation - Includes the ions that ParticiPate in the reaction
lons that don't participate in the reaction are called spectator ions.