Unit 3
Sig-digs
digits in a number that contributes to the precision
there are sig-dig laws that determine the result
non zero digits
numbers 1-9 are significant
leading zeros
any 0 before a significant number doesn’t matter
captive zeros
any 0 in between significant numbers matter
trailing zeros
any 0 that trail a significant number but around a decimal point, matters
exact numbers
numbers that are counted or have a defined quantity, have an infinite amount of sig-digs
Formulas
exothermic = E bond breaking < E bond forming = E required < E released
endothermic = E bond breaking > E bond forming = E required > E released
%mass=mass solute/mass solution x 100%
ppm=mass of solute/mass of solution x 10^6
n=m/M
C=n/V
C1V1=C2V2
Kw (1.0 × 10^-14 (mol/L)²) = [H3O+(aq)][OH-(aq)]
[H3O+(aq)] = 10^-pH
[H3O+(aq)] = Kw/[OH-(aq)]
pH = -log[H3O+(aq)]
[OH-(aq)] = 10^-pOH
[OH-(aq)] = Kw/[H3O+(aq)]
pOH = -log[OH-(aq)]
pH + pOH = 14.00
Solutions
Matter
Anything with mass and volume
Mixture
combinations of matter that can be physically separated
Does not have a definite composition
Types of mixtures
Heterogenous Mixture (Mechanical Mixture)
Different components of the mixture are visible
Composition is variable throughout the mixture
Homogenous Mixture (Solution)
Different components are not visible
Composition is constant throughout the mixture
Pure Substances
A matter with a definite composition
Types of pure substances
Element
cannot be chemically broken down into simpler substances
Compound
two or more elements that are chemically combined
Solutions
A solution is a type of a homogenous mixture
solvent
a solvent is the dissolver where a substance dissolves in the solvent and is usually has the largest quantity of substance (could be in mass, volume or amount)
solute
a solute is the substance what dissolves within the solvent
Aqueous solution
any solution that has water as its solvent
Electrolytes (ionic compounds)
aqueous solutions that conduct electricity
All soluble ionic compounds will form electrolyte solutions when dissolved in water
Non-electrolytes (molecular compounds)
aqueous solutions that do not conduct electricity
Molecular compounds that are able to dissolve in water will produce a non-electrolytic solution
Most molecular compounds do not dissolve in water
The process of dissolving
dissolving is a physical change not a chemical change
When dissolving occurs, the intermolecular bonds between the solute particles break apart. Some of the intermolecular bonds between solvent particles must also break
When individual solute become attracted to solvent particles, they form new intermolecular bonds between the solute and solvent
Changes caused by dissolving
Physical changes
the breaking down and formation of intermolecular bonds
Chemical changes
the breaking down and formation of intramolecular bonds
Breaking
as a solute dissolves, it requires energy to break bonds
An endothermic reaction is caused as energy is being used to break the bonds, absorbing heat from the surroundings as there is a greater amount of energy from bond breaking than bond forming
Forming
as a solute dissolves, it releases energy from forming bonds
An exothermic reaction is caused as energy is being used to form bonds, losing heat to the surroundings as there is a greater amount of energy from bond forming than bond breaking
Dissociation reactions
reactions that show how a soluble ionic compound breaks apart into its ions when dissolved in water
Solubility
solubility
the solubility of a solute is the amount of a solute that can dissolve in a given quantity/amount of a solvent at a given temperature
types of solubility
Unsaturated solution
a solution that does not have the maximum amount of solute dissolved in it
Saturated solution
a solution that contains the maximum amount of dissolved solution at a given temperature
Supersaturated solution
a solution that contains more dissolved solute than its solubility value at a given temperature
Solubility value
the solubility value of a solute is the concentration of a saturated solution. A concentration value indicates how much solute (usually in moles) is dissolved in a certain amount of solvent (usually in litres)
Chemical solubility
dissolving
compound to elements, decomposition
crystallization
elements to compound, formation
Equilibrium
If the dissolving rate is taking place at the same rate as the crystallization, the saturated solution is said to be at equilibrium
Both dissolving and crystallization take place at the same rate
temperature with solubility
solid dissolves in a liquid
solubility of the solid increases with temperature increasing
liquid dissolves in liquid
solubility of the liquid is not affected by temperature
gas dissolves in a liquid
gas particles need to lose enough kinetic energy so that they can slow down to be allowed to dissolve into the liquid
solubility of the gas decreases with temperature increases
pressure
pressure can affect the solubility of gases
as pressure increases, the solubility of gases increases
the solubility of solids and liquids are not affected by pressure
Concentration
concentration
concentration is defined as the amount/quality of solute relative to the amount/quantity of solvent
dilution
a solution is considered dilute when there are relatively small amounts of solute dissolved in a large amount of solvent
concentrated
a solution is considered concentrated when there is a large amounts of solute dissolved in a large amount of solvent
percent by mass
a concentration that compares the mass of a solute to solvent, expressed as a percentage
%mass = mass solute/mass solution x 100%
parts per million (ppm)
the concentration of a solute in a million parts of a solution or used to measure small amounts of concentration
ppm = mass of solute/mass of solution x 10^6
conversions
1 kg = 1000 g = 1000000 mg
1 L = 1000 ml
1 g = 1 ml
molar concentration
molar concentration or molarity indicates the number of moles of solute dissolved in one liter of solvent
concentration = number of moles of solute / volume of solvent in litres (C=n/V)
molarity
another term for concentration
Standard Solution
a solution with a known concentration is called a standard solution
there are ways to make a solution of a known substance
dissolve a measured amount of pure solute in a certain volume of solvent
dilute a standard solution to a desired concentration
Dilutions
dilutions occur when the concentration of a solution is decreased by adding more solvent
the intensity of the colour can be used to compare the concentration of solutions, where the more intense the colour, the more intense the concentration of the solution
the way to compare is by comparing the initial concentration and volume solution to the final concentration and volume
Flasks
Erlenmeyer
conical shape with a flat bottom
ideal for mixing and heating as it has a narrow neck to minimize evaporation
Volumetric
long neck and flat bottoms, with specific marked measurements
used for precise dilutions and preparation of standard solutions
Boiling/Florence
round bottom and a narrow neck
used for boiling as it distributes heat evenly
Beaker
cylindrical with a flat bottom
not a flask but is commonly used, suitable for mixing and heating but not for measurements
Meniscus (not a flask)
this is the surface tension of a solution that dips down (if concave, up if convex) when in a flasks neck, this can be used to measure the amount of solution in a flask
Pipette (not a flask)
long and narrow instrument
used to make precise measurements, measure liquids and transferring liquids
Historical definitions of acids and bases
Humphrey Davy: first stated that the presence of hydrogen gave a compound acidic properties (wrong)
Justus von Liebig: stated that acids are ionic compounds in which a hydrogen ion (H+) replaced a cation
Savante Arrhenius: stated that acids are substances that ionize in aqueous solutions to form hydrogen ions and bases are substances that disassociate to form hydroxide ions in aqueous solutions
Paul Giguère: discovered that hydrogen ions are unlikely to exist in solution- instead it is more likely that they are attracted to and combine with water to form a hydronium ion
Modern definition: the hydronium ion is responsible for acidic properties and hydroxide ions are responsible for basic properties
Self-ionization
when molecules collide, a hydrogen ion (proton) is transferred from one water molecules to another, resulting in the production of a hydroxide ion and a hydronium ion - a solvated proton
Self-ionization of water occurs for about 1 water molecule in every 500 million - the majority of water remains as H2O
H2O[l] + H2O[l] —> H3O+[aq] + OH-[aq]
Determining Acid and Base solutions
pH meter
a pH meter measures a small voltage produced by a solution containing hydronium ions and converts the electrical measurement into a pH reading
acidic solution: [H3O+(aq)] > 1.0×10^-7 mol/L = pH < 7
basic solution: [H3O+(aq)] < 1.0×10^-7 mol/L = pH > 7
if the concentration of the hydrogen ion increases, then the concentration of the hydroxide ion decreases, and vis versa
How to solve problems using Kw
write a balanced dissociation equation
if concentration is not given, determine the concentration of at least one substance
do a mole-mole ratio to determine the ion concentration of either the hydronium ion or the hydroxide ion
solve using Kw
pH and H3O+(aq), hydronium ion concentration
pH stands for the power of hydrogen and ranges from 0 (very acidic) to 14 (very basic)
each pH change is is equal to a change in the hydronium ion concentration of 10
If [H3O+(aq)] goes up, then pH goes down; solution becomes more acidic
If [H3O+(aq)] goes down, then pH goes up; solution becomes more basic
with hydronium ion concentration and pH, the number of decimal places in the pH is equal to the number of significant digits for the hydronium ion concentration, and vis versa
pOH and Hydroxide ion concentration
while pH is more common, hydroxide ion concentration or a pOH can be more convenient or practical to describe
if [OH-(aq)] goes up, then pOH goes down and solution becomes more basic
if [OH-(aq)] goes down, then pOH goes up and solution becomes less basic and more acidic
pH Scale
measures the H3O+ of a solution
everything above 7 and to 15 = base
everything below 7 and to -1 = acid
7 = neutral
each change in pH is equal to a change in hydronium ion concentration of 10
pOH Scale
measures the OH- of a solution
everything above 7 and to 15 = acid
everything below 7 and to -1 = base
7 = neutral
each change in pOH is equal to a change in hydroxide ion concentration of 10
Arrhenius Theory
old definition
ionic compounds dissociate into separate cations and anions when they dissolve to form a solution
acids are substances that ionize in aqueous solutions to form hydrogen ions
bases are substances that dissociate to form hydroxide ions in aqueous solutions
modernized definition
acids are substances that react with water to produce hydronium ions
bases are substances that react with water o produce hydroxide ions
what the theory was updated
collisions of dissolved substances with water molecules
the nature of the hydrogen ion
due to collisions between water molecules, hydrogen will ionize to form a hydronium ion and hydroxide ion
How to write equations using Modified Arrhenius Theory
Idk bro
Neutralization Reactions
a neutralization reaction is a reaction between a hydronium and a hydroxide ion to produce water
Acids
empirical properties
weak acids
strong acids
polyprotic acids
Bases
empirical properties
weak bases
strong bases
polyprotic/polybasic bases
monophonic bases/monobasic bases