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7/28/2019 [Notes]CHEM15.1 - Fundamentals of Chemistry: Laboratory
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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the curved surface of the water iscalled the meniscus
to read the volume of a liquid, keepyour eye on the same level with thelowest point of the meniscus
decantation is a process of separating a liquid from a denseinsoluble substance by pouring off the liquid
the liquid that is poured off during decantation is called the supernatant liquid
the separation of a solid from a liquid by passing the liquid through a
membrane is called filtration the liquid that passes the membrane is called the filtrate while the remaining
solid is called the residue
trailing zeros (zeros at the end after the decimal point) are significant
captive zeros (zeros within non-zeros) are significant
leading zeros before a decimal point are not significant but significant after the decimal point
final zeros that denote exact numbers are significant; not significant if the
number is only an approximation an exact number has an infinite number of significant figures
add or subtract decimals then round it off to the nearest least number of digits
multiply or divide decimals and reduce it to the least number of significantfigures in one of the dividend/divisor/factor
Measurements
quantitative observation
to be meaningful it must consist of a number and a scale expands by what our senses can perceive
SI System of Measurement
organized to standard systems of measurement in the world
made to avoid confusion created by the existence of metric and Englishsystem
SI Prefixes Common to Chemistry
Prefix Unit Abbr. Exponent
kilo 103
deci
10
-1
centi 10-2
milli 10-3
micro 10-6
Metric conversions – conversions in
Note: Graduated glassware canonly accurately measure liquids of
10% to 100% of its volume.Note: Use the forefinger in using apipette.
Note: A parallel-oriented plug givesa voltage of 220V while a straightplug gives a voltage of 110V.
Physical Quantity Unit
Length meter ()
Mass kilogram ()
Time second (
)
Temperature Kelvin ()
Luminous intensity candela ()
Electric current Ampere ( )
Amount of substance mole ()
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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the metric system are merely a matter of moving a decimal point. The “base unit”means that you have a quantity without a prefix.
Uncertainty in measurements
a digit that must be estimated is called uncertain
a measurement always has some degree of uncertainty
calibration is the difference among the smallest division
Precision and Accuracy
accuracy refers to the agreement of the measured value with the true value
expressed in % error
% =measured-true
true× 100%
a lower value means greater accuracy depends on the capacity of the instrument and its calibration as well as on
the person determining the instrument
precision is the agreement among values
expressed in terms of average deviation
measured-average
a lower value means greater precision
depends on the person making the measurement
Importance of the following steps addition of water – to dissolve the water-soluble component in the mixture
boiling the water – to further dissolve the water-soluble component
filtration – to separate the residue (water-insoluble component) from the filtrate(water-soluble component)
washing the residue with hot water – to ensure that all water-solublecomponent will be separated from the residue and transferred to the filtrate
evaporation – as water evaporates, the residue (water-soluble component) isleft behind, returns to its original state and thus capable of being weighed for subsequent calculations
Reminders during the experiment
use low blue flame when evaporating
to avoid splattering which could result to loss in mass of water-solublecomponent
further consequence is lower percentage of water-soluble component
weigh evaporating dish only when it is already cooled at room temperature
weighing while hot results in lower mass of water-soluble component
Errors in the experiment
low sensitivity of some instruments resulting in probable inaccuratemeasurements
basic assumptions like all water-soluble component are soluble and water-insoluble component remains insoluble in water
errors due to splattering and weighing of evaporating dish while hot
human errors
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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Graphs
quick way to represent data visually in a compact and convincing way especially useful in analyzing huge amounts of data
can be pie, linear, bar, cone, etc.
Reminders in making a good graph1] figure titles
should be appropriate with the data it represents
located below the graph
should have a period at the end
order of graphs is usually indicated by a number 2] labels of axes
-axis goes with the independent variable
-axis goes with the dependent variable
units of variables are also included and are enclosed in parentheses3] proper scaling observation
scales within each axis should be consistent; if differences in scaling is 5units, then use 5 all throughout, not 10 nor 2 in some parts of the axis
start your scale with a number slightly lower than the smallest data;similarly, end your scale with a number slightly higher than the largest data
use the lightning-like figure in axis when dealing with data that areenormously large; this will save up space and will make scaling relatively
easy4] best-fit curve
this is the line that goes through almost all data points
an advantage of using this line is that it excludes the errors of the data
Slope
∆ ∆
indicates the relative steepness of the line
the larger the slope value, the steeper the line
Interpolation process of locating points within the graph
usually the dependent variable is the one missing or to be calculated
only reliable if data projects a trend or set of data has minimum errors
starting from the -axis, a broken line is written until it reaches the line graph
and then projected into the -axis
the data on the -axis is the corresponding data for the -value in question
On preparing the graph1] indent the axes from the edge of the graphing paper 2] write the appropriate figure number and title of the graph below it3] identify the independent and dependent variables4] label each axis and indicate the units used5] choose an appropriate scale6] plot the points in the graph7] draw the (best-fit) curve
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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Matter is anything that occupies space and has mass.
Composition refers to parts or components of a sample of matter and their relative proportions. Composition is seen through the models, properties,similarity among elements/compounds) and differences amongelements/compounds.
Properties refer to qualities or attributes that can be used to distinguish onesample of matter from the other. This is usually established visually.
Physical Property is a property that a sample displays without changing itscomposition. Physical change refers to the change of physical appearance of asubstance. Some of the physical properties of a sample of a matter may change,but its composition remains unchanged. Phase change is also an example of
physical change.Chemical property refers to the ability (or inability) of a sample of a matter to
undergo a change in composition. Chemical change happens when a sample of matter is converted into a new sample with different composition. It can occur even without addition of a chemical or a reagent. Indications of chemical changeinclude evolution of gas, increase in temperature, change in color, and formationof precipitates.
Elements are homogenous pure substances that are made up of only oneatom. They cannot be broken down into simpler substances.
Compounds are homogenous pure substances that are made up of two or
more atoms. They can be broken down into simpler substances throughappropriate chemical means.
Homogenous pure substances have uniform composition and propertiesthroughout a given sample.
Homogenous mixtures have uniform composition ad properties throughout agiven sample, but the composition and properties may vary from one sample toanother.
Heterogeneous mixtures have components that are separated into distinctregions, making the composition and property vary from one mixture to another.
Homogenous substances cannot be easily identified as a mixture andtherefore needs a device like a microscope. Mixtures can be separated into itscomponents by appropriate chemical changes.
Boiling point
temperature at which the vapor pressure equals the standard atmosphericpressure
temperature at which liquid converts to a gas
the boiling point of pure substances is constant and straight; the boiling pointof mixtures varies across time
Intensive properties are independent of the quantity of matter under observation. Extensive properties are, by contrast, dependent of the quantity of matter
Electrons
located outside the nucleus and has a negative charge
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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discovered by Eugene Goldstein
can probably be located 90% of the time in one of the orbitals
Quantum numbers
describe the orbitals
have discrete quantities (either an integer or half-integer
has four kinds
principal quantum number,
refers to the main energy levels which describes the probable distance of the electron from the nucleus
can take positive integer values starting from 0
angular momentum / azimuthal quantum number,
refers to the shape of the orbitals which is the surface that contains 90%of the total electron probability
can take positive integer values from 0 to − 1 o the orbital has a spherical shape centered around the origin of the three
axes in spaceo there are three dumbbell-shaped orbitals in each energy level above
= 1, each assigned to its own axis in spaceo things get a bit more complicated with the five orbitals that are found in
the sublevels beginning with = 3
magnetic quantum number, refers to the spatial orientation of the electrons
can take integer values from −ℓ to ℓ, including 0 spin quantum number,
refers to the electron spin which describes the behavior of an electronwithin a magnetic field
can take either + 12 or −1
2
An orbital is a region in the atomic space where the electron is most likely tobe found. It is characterized by a set of quantum numbers.
Pauli’s Exclusion Principle states that in a given atom, no two electrons can
have the same set of four quantum numbers.Aufbau Principle states that electrons would most likely occupy the lower
energy orbitals first before continuing to the next orbitals. Identifying the lower level orbitals is determined by the ( + ) rule, which states that the lower the
( + ℓ) value, the lower the energy of the orbital. In case of equal + ℓ, theorbital with the lower has the lower the energy.
Hund’s Rule states that every orbital in a subshell is singly occupied with oneelectron before any orbital is doubly occupied, and all electrons in degenerateorbitals have the same spin.
To get the valence electron configuration of an atom, identify the
corresponding orbitals of a given principal quantum number. Only thecorresponding orbitals of the last principal quantum number will be used for thevalence electron configuration.
To get the noble gas configuration of an atom, identify the electronconfiguration of the highest possible noble gas that is lower than the given atom.Then replace that part of the configuration found in the electron configuration of the atom with the chemical symbol of the noble gas enclosed in braces.
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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The effective nuclear charge, denoted as Zeff , is the net positive chargeexperienced by an electron in a many-electron atom. = − where is the
shielding constant exerted by the electrons.
* doesn’t applywith noble gases
Rules for namingbinary
compounds:
1] identify the elements present in the compound given by the chemical formula 2] change the suffix of the less metallic element to –ide* 3] use the prefix corresponding to the number of atoms present in the compound
* In accordance with established practice, the elements in a covalent compoundare placed and named first in the sequence: Rn – Xe – Kr – Si – Sb – B – As – P – H – Te – At – Se – C – I – Br – N – Cl – O – F
Rules for writing chemical formulas of binary compounds:1] represent each kind of element in a compound
2] indicate by a subscript the number of atoms of each element in a molecule of that compound3] write the symbol of the more metallic element first (H is an exception)
Rules for naming ionic compounds:1] write the name of the cation first, followed by the name of the anion2] write the suffix of the cation depending on the charge (refer to a table) and
replace the suffix of the anion with –ide
Rules for writing chemical formulas of ionic compounds:1] write the symbol of the cation followed by the symbol of the anion
2] balance the charge of the ions to have a net charge of 0 by adding or removing instances of ions
3] for hydrates, follow the chemical formula with a central dot and the correctamount of water molecules
Rules for naming binary acids
if a binary acid, fill the prefix of the anion to hydro_____ic
if an oxyacid…
if the anion ends in –ate, fill the prefix of the anion to _____ic acid
if the anion ends in –ite, fill the prefix of the anion to _____ous acid
A mole is a quantity that contains approximately 6.02×1023
particles. It isdefined as the quantity of a substance that contains the same number of particlesas are contained in precisely 12.00g of a particular isotope of Carbon, 12C.
Atomic Property Trends
Greater at lower-left Greater at upper-right
Atomic Size First Ionization Energy
Cation Formation Tendency* Anion Formation Tendency*
Electron Affinity*
Electronegativity
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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= =
no.of particles
Boyle’s Law states that at constant temperature, the pressure of a givenamount of gas is inversely proportional to its volume. The product of pressure
and volume is equal to a constant. = 1 Charles’ Law states that at constant pressure, the volume of a given amount
of gas is directly proportional to its absolute or Kelvin temperature. The ratio of
volume to the temperature is equal to a constant. = 2
Avogadro’s Law states that at a give temperature and pressure, the volumeof gas is directly proportional to the quantity of gas, in moles. The ratio of volume
to the amount of gas in moles is equal to a constant. = 3 Using all three laws, the result can be expressed in the terms of = ,
which is the ideal gas law, where is the pressure of gas (in atm), is the
volume of gas (in L), is the number of moles of gas, is the temperature (in
Kelvin), and is the ideal gas constant, which is equal to 0.0821∙∙.
In 1916, Gilbert Newton Lewis represented the structure of elements andcompounds by using the symbol of the elements, and dots representing valenceelectrons. This is later on referred to as the Lewis structure.
The Lewis structure of ionic compounds usually has the cation permanentlytransferring electrons to the anion, instead of atoms bonding.
The Lewis structure of covalent compounds usually has bonds that hold theatoms together in a molecule which are called covalent bonds, unlike in ioniccompounds.
The octet rule states that an atom other than hydrogen tends to form bond/suntil it is surrounded by eight valence electrons.General guidelines for writing Lewis structure of simple molecules
determine the number of valence electrons to be distributed in the Lewis
structure write a skeletal structure for the molecule indicating the arrangement of the
atoms and which ones are bonded to one another
place one pair of electrons between each bonded atom to make a single bondbetween each pair of bonded atoms
use the remaining electrons, place lone pair around the terminal atoms tosatisfy the octet rule
if there are still remaining electrons, place them around the central atom aslone pairs
move the electrons to form double or triple bonds in order to satisfy the octet
rule for the central atom
Resonance structures are Lewis structures of the same molecule that aresame in structure but have different electron and bond placement.
Three exceptions to the octet rule
incomplete octet have less than eight electrons surrounding the central atom
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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expanded octet have more than eight electrons surrounding the atom (byusing the d orbitals)
odd electron species or free radicals are species that have an unpairedelectron
The formal charges of atoms are apparent charges on atoms in a Lewisstructure. It is calculated using this:
formalcharge
=
number of valence electronsin the free atom
− number of
non-bondedelectrons
−
½ of the totalnumber of bondingelectrons
There are guidelines in selecting the most plausible resonance structure usingthe formal charges:
for neutral molecules, the Lewis structure with atoms bearing the lowest formalcharges (closest to zero) is most preferred
the most electronegative atoms in a Lewis structure should bear negativeformal charges while the least electronegative atoms should bear positiveformal charges
adjacent atoms in a Lewis structure should not have formal charges of thesame sign
Molecules are stable units formed by sharing electrons through intermolecular
bonding. They don’t exist in metals, ionic compounds or covalent networksubstances.
Intermolecular Forces of Attraction
forces causing aggregation of compounds of a substance to form a liquid or solid
occurs between rather than within molecules
responsible for changes in physical states
affects boiling point, vapor pressure, viscosity, and surface tension
Types of IMFA
London dispersion forces are weak and short-lived forces of attraction thatexists in all molecules
Dipole-dipole interaction exists in polar molecules which exhibit dipolemoment
Hydrogen bonding
strong dipole-dipole forces
seen in molecules where it is covalently bound to any of highlyelectronegative elements N, O, or F
objects are electrically charged by rubbing
electrical charges of opposite signs attract each other
Surface tension is a property possessed by liquid surface whereby theyappear to be covered by a thin elastic membrane in a state of tension.
For a given volume of a substance, the shape with the least surface area is asphere.
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Solids are substances that have definite volume and shape. Pure solid
substances are classified into four different types: metallic substances
ionic solid
covalent molecular
covalent network
Electrical conductivity
ability to conduct electric current which requires movement of chargedparticles
differences in conductivity lie mainly on
the kind of particles present
forces of attraction existing between particles
Metals
structural unit is composed of positive ions, metal atoms, surrounded by sea of delocalized electrons
force of attraction that holds the metal atoms together is the metallic bonding, joined by extreme delocalized bonds
metals conduct electricity in their solid and molten state but in aqueous state,which are insoluble except for some which react
electron sea model is composed of…
cations – particles which form the crystal lattice; occupy fixed positions in alattice or array
sea of electrons – electrons list by metal atoms; electrons move freely in thelattice
The introduction of an electric field to the metal in its solid or molten statescauses these electrons to flow, producing electric current.
Ionic substances
structural unit is composed of ions bound by ionic bonding
ionic substances conduct electricity in their molten and aqueous state but not
in solid state electrolytic conduction occurs in ionic substances in the molten or aqueous
state.
Covalent molecular compounds
structural unit is composed of atoms or molecules bonded by covalent bondingand interacts using IMFA
covalent molecular substances do not conduct electricity in any state exceptfor some when dissolved in water
molecular compounds do not conduct electricity unless they react with H2O
(ex. HCl) to form ions; the molecules are electrically neutral and there are nocharged carriers
Covalent Network
structural unit is composed of atoms joined together by covalent bonding
covalent network substances do not conduct electricity in any state and areinsoluble in water
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CHEM 15.1 Notes by F5XS Fundamentals of Chemistry: Laboratory
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graphite is an exception as each carbon is bonded to three other carbon andone electron is delocalized; diamond does not conduct electricity since each
carbon atom is bonded to four other carbon atoms
Energy is the capacity to do work.The law of conservation of energy states that energy can be converted from
one form to another but can neither be created nor destroyed.Potential energy is the energy due to the position or composition of the
substance while kinetic energy is the energy due to motion.Temperature is a property of substances that reflects the random motion of
particles in a particular substance while heat is the transfer of energy betweentwo objects due to temperature difference. Temperature reflects the intensity of
the random kinetic energy in matter while heat is the amount of energy availablefor heat flows depends on quantity of matter at a given temperature.
A cooling curve is a graphical representation of the changes of states withuniform removal of heat from a substance.
At 0 to 1, as heat is removed from the gas, the average kinetic energy of theparticles of the gas decreases and the temperature drops until the temperature is
reached at 1 where the gas starts to liquefy. The temperature at which the gasand liquid coexist is the liquefaction or condensation point of the substance. Theliquefaction point and the boiling point of a substance are, therefore, equivalent.
At 1 to 2, also known as the liquefaction/condensation point, there is nochange in the average kinetic energy of the particles and so the temperature of the substance stays constant. The heat removed is, therefore, compensated for by the release of the stored potential energy, decreasing the potential energy of the substance. The amount of gas naturally decreases and the amount of liquid
increases. Eventually, at 2, sufficient heat has been removed to convert all thegas to liquid.
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At 2 to 3, as heat is removed, the average kinetic energy of the particles of
the liquid decreases and the temperature drops until the temperature at 3 isreached where the liquid starts to solidify. The temperature at which the liquidand solid coexist is the freezing or crystallization point of the substance. Thefreezing point and the melting point of a substance are, therefore, equivalent.
At 3 to 4, also known as the freezing point, there is no chance in the
average kinetic energy of the particles and so the temperature of the substancestays constant. The heat removed is compensated for by the release of storedpotential energy, decreasing the potential energy of the substance, as the liquidparticles are converted to solid. The amount of liquid gradually decreases and
the amount of solid increases. Eventually, at 4, sufficient heat has been removed
to convert all the liquid to solid.
The Phenomenon of Supercooling At the expected freezing point of a substance, the particles may not be
oriented properly to fit the crystalline lattice. When heat continues to be removedfrom the substance in the absence of crystallization, the temperature of the liquiddrops down below its expected freezing point and the liquid is said to besupercooled. Once the correct pattern has been built up to sufficient size,additional particles may rapidly accumulate. Potential energy is suddenlyreleased and the energy that is evolved increases the average kinetic energy of the particles and the temperature rises until it coincides with the freezing point
after which the substance behaves normally.Supercooling may be reduced by the introduction of a seed crystal, on which
crystallization can occur, thereby initiating the proper structure. As some substances like glass, rubber and many plastics are cooled, their
molecules move so slowly that they never find the proper orientation to form thecrystalline solid and an amorphous solid results instead. Amorphous solids areactually supercooled liquids which do not have a sharp, well-defined meltingpoint, but instead gradually soften when heated.
A heating curve (see next page) is essentially the opposite of a cooling curve.It graphically illustrates the changes of states with uniform addition of heat to asubstance. The distance of the time axis is a measure of the amount of heatadded at a constant rate.
At 0 to 1, as heat is added to the solid, the motion (kinetic energy) of theparticles of the solid increases and the solid progressively becomes slightly lessordered. Since temperature measures kinetic energy, the temperature rises untilthe temperature is reached at 1 where the solid starts to melt. The temperatureat which solid and liquid coexist is the melting point of the substance.
At 1 to 2, also known as the melting point, there is no change in the average
kinetic energy of the particles and so the temperature of the substances staysconstant. The added heat is used to overcome the forces of attraction betweenthe particles of the solid and is thereafter stored as potential energy, increasingthe potential energy of the substance. The amount of solid gradually decreases
and the amount of liquid increases at this point. Eventually, at 2, sufficient heathas ben added to convert all the solid to liquid.
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At 2 to 3, as heat is added, the average kinetic energy of the particles of theliquid increases and the temperature rises until the temperature at 3 is reachedwhere the liquid starts to evaporate. The temperature at which liquid and gascoexist is the boiling point of the substance.
At 3 to 4, also known as the boiling point, there is no change in the averagekinetic energy of the particles and so the temperature of the substance staysconstant. The added heat is used to overcome the forces of attraction betweenthe particles of the liquid and is stored as potential energy, increasing thepotential energy of the substance. The amount of liquid gradually decreases andthe amount of gas increases. Eventually, at 4, sufficient heat has been added toconvert all the liquid to gas.
The Phenomenon of SuperheatingThe bubbles formed at the boiling point provide internal space at which the
liquid can evaporate. Bubbles form easily in a vessel with irregular inner surface.In a vessel with smooth inner surface, bubbles may not form easily so that theliquid is heated to a temperature above the boiling point without evaporation. Thisprocess is known as superheating.
At the first and second graphs of the cooling curve, the melting point range isobtained. This usually occurs when the substance contains impurities. At thethird graph, the temperature rise denotes that a substance has supercooled.
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Types of chemical reactions combination [A + B + ⋯ → C] reactions involve two or more elements or
compounds reacting to form a bigger compound
in a decomposition [A → B + C + D + ⋯] reaction, a single compound isbroken down into two or more simpler substances; usually requires heat whensolid is being decomposed
in a single displacement [AB + C → AC + B] reaction, either the cation or anion of an ionic compound is replaced by an uncombined element
double displacement [AB + CD → AD +C B] reaction
a precipitation reaction is a type of double displacement reaction wheretwo ionic compounds dissolved in water are combined to form two new onesby exchanging cations and anions with one another, with one of theresulting compounds soluble in water while the other is insoluble
a neutralization reaction involves the reaction between an acid and a baseto form water and a salt
combustion is a special type of reaction which involves the reaction of asubstance with oxygen and evolution of heat
Rules on solubility
most nitrates (NO3-) are soluble
most salts containing alkali metal ions (Li+, Na
+, K
+, Cs
+, Rb
+) and the
ammonium ion (NH4+) are soluble
most chlorides (Cl-), bromides (Br
-), and iodides (I
-) are soluble except Ag
+,
Pb2+
, and Hg22+
most sulfate salts are soluble except BaSO4, PbSO4, HgSO4, and CaSO4
most hydroxide salts are only slightly soluble while Ba(OH)2, Sr(OH)2, andCa(OH)2 are marginally soluble
most sulfide, carbonate, and phosphate salts are only slightly soluble
Chemical Equations represents the changes that take place during chemical
reactions.
Balancing chemical equations show substances that reacted andsubstances produced and the amount of each substance on both sides.
The coefficients before the substance denotes the relative amounts of substances involved.
2H2 + O2 → 2H2Oreactants products
Physical states of substances when balancing chemical equations includesolid, liquid, gas, and aqueous state.
Chemical Stoichiometry
quantitative relationship of the amounts of reactants and amount of productsformed
mass relationship expressed in a balanced reaction
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factors that limit the yield of products in a reaction are…
amount of starting reaction
percent yield of reaction which are affected by changes in pressure andtemperature
chemicals react according to fixed mole ratios
only a limited amount of product is formed from a given amount of startingmaterials
the limiting reactant is complete consumed and determines the amount of product formed while the excess reactant does not completely get used up ina reaction
A solution is a homogeneous mixture composed of a solute and a solvent.The solvent is the component that retains its state when solution is formed anddissolves the other component. When both components are liquid, the substancewith higher amount is chosen as solvent. The solute is the component beingdissolved by the solvent.
A solute is said to be soluble if it is a solid dissolved in the solvent while it issaid to be miscible if it is a liquid dissolved in the solvent.
A dissolution process is said to be exothermic if the process involvesreleasing of heat while it is said to be endothermic if the process involvesabsorption of heat.
Solubility refers to the maximum amount of solute that is dissolved in a givenamount of solvent at a given temperature. There are three factors affectingsolubility:
pressure
as pressure is increased, the number of collisions of gas particles with thesurface of the liquid increases, thus the rate of capture of gas molecules bythe liquid also increases
temperature
solubility of gases in liquids
as temperature is increased, there results in an increase in kinetic energyof the gas molecules, thus a large fraction of gas molecules will possess
the kinetic energy required enabling them to escape from the liquid solubility of solids in liquids
may either increase or decrease with the change in temperaturedepending on whether the solution process is endothermic or exothermic
if a dissolution is exothermic, then an increase in temperature willincrease the solubility of the liquid
if a dissolution is endothermic, then an increase in temperature willdecrease the solubility of the liquid
as temperature is increased, entropy is also increased; the dissolution of solids in liquid is thus favored because the liquid state is more disorderly
than the solid state nature of solute and solvent
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Types of solutions based on the relative amount of dissolved and undissolvedsolute:
saturated, if a solution that contains the maximum amount of solute that candissolve in a given volume of solvent and has a concentration equal to thesolubility of the solute
unsaturated, if a solution contains an amount of solute less than its solubility
supersaturated, if the solution may contain an amount of solute greater thanits solubility under special conditions
There are three important interactions that operate in the solution process:
solute-solute interactions
attraction between the solute particles
in overcoming these forces of attraction that bind solute particles together,
energy must be supplied to the system solvent-solvent interactions
attraction between solvent particles
this is energy-requiring since you are pushing apart the solvent to providespace to accommodate solute particles
solute-solvent interactions
attraction between the solvent and solute particles
the formation of these forces of attraction should provide the energyrequired to overcome both the solute-solute and solvent-solvent interactions
the stronger the attractive forces between unlike molecules of particles, thegreater the solubility
a polar substance will most likely dissolve a polar substance while a nonpolar substance will most likely dissolve a nonpolar substance
A reduction-oxidation reaction, or simply redox reaction, is a reactionwhich involves the transfer of electrons from one substance to another.
Oxidation is a half reaction that involves the loss of electrons while reduction is a half reaction that involves the gain of electrons.
The oxidizing agent is a reactant which oxidizes the other reactant and whichundergoes reduction. The reducing agent is a reactant which reduces the other reactant and which undergoes oxidation.
The standard reducing potential table is a list of oxidizing agents, in order of
increasing strengths with corresponding potentials, denoted by °. ° isdetermined by comparing with the potential of standard hydrogen electrode (one
mole in aqueous solution or 1 for gases at 25°)
Identifying half reactions
reduction half-reaction (RHR) involves the gain of electrons; electrons
appear on the reactant side oxidation half-reaction (OHR) involves the loss of electrons; electrons
appear on the product side
On determining the reducing agent, oxidizing agent and their relative strengths
potential, also called voltage or electromotive force, unit: volts, is themeasure of the tendency of the half reaction to occur
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reduction potential is the tendency of species to acquire electrons; the morepositive the reaction, the greater is the tendency to occur
oxidation potential is the tendency of species to lose electrons
Voltaic/Galvanic Cell
named after Luigi Galvani andAlessandro Volta
an electrochemical device wherea spontaneous oxidationreduction takes place andgenerates electrical energy
salt bridge contains aconcentrated solution of a strong
electrolyte; thus ions diffuse outof the solution
the cation and the anion to beused should be about the samesize and of the same magnitudeso that they diffuse at the samerate; they must also be inert towards the solutions and towards the electrons
Cell Potential is the potential of overall reaction of the redox reaction. It iscomputed by getting the sum of the potentials of the two reactions.
The sodium hydroxide pellets should increase in mass after standing becauseit is hygroscopic. Thus, there is a need to standardize the sodium hydroxidesolution because its concentration would not be exactly 0.1M because its massincreased.
Rates of Reaction
change in concentration of a reactant on a per unit time
expressed in terms of the increase in the concentration of a product per unittime, or the decrease in concentration of reactant per unit time
Factors affecting rate of reaction
nature of reacting species
concentration
temperature
presence of a catalyst
Collision Theory of reaction rates
for a chemical reaction to occur, the reacting species should collide with eachother
the collision may or may not be effective; a collision is effective when it resultsin a chemical reaction
for an effective collision to occur…
reacting species must have a particular orientation during collision
the collision must occur with enough energy, called activation energy
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Reaction Pathways
Reaction pathway for an exothermicreaction
Reaction pathway for an endothermicreaction
Effect of concentration on rate of reaction
Reaction pathway for an uncatalyzedreaction
Reaction pathway for an catalyzedreaction
the catalyst lowers the energy barrier but does not affect the actual energy of products or reactants
state of equilibrium exists not only in gaseous systems but also in reactionsoccurring in solutions
a chemical equilibrium is a state where the concentrations of all thereactants and products remain constant with time
The following conditions exist when a process has reached a state of equilibrium:
a dynamic situation in which the forward and reverse processes continue totake place though the reaction appears to have stopped
a balance in which the rate of formation of the products is just equal to therate at which they are being decomposed
a definite mathematical relationship
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if > 1, more of the product is formed, and the direction of the reaction is
forward
if < 1, more of the reactant is formed, and the direction of the reaction isbackward
if = 1, the reaction is in a state of chemical equilibrium
Effect of concentration (Fe3+ + SCN− ⇔ FeSCN2+)
increase of Fe3+ from Fe
NO33
increases the rate of forward reaction
increases in collisions to form more FeSCN2+ until another equilibrium isreacted
equilibrium shifts forward
a darker solution was observed because of the increase in FeSCN2+
increase of SCN from KSCN−
increases the rate of forward reaction
increases in collisions to form FeSCN2+ until another equilibrium is reached
increase in H2PO4−
decreases the concentration of free Fe3+ because of the reaction: Fe3+ +
H2PO4− ⇔ FeH2PO4
2+ (colorless)
Generalization: Increasing the concentration of a substance in equilibriummixture displaces the equilibrium in the direction which consumes some of theadded materials. Conversely, decreasing the concentration of a substance favors
the reaction which produces it.
Effect of pressure (2NO2 ⇔ N2O4)
the gaseous equilibrium is initially brown; initially after pushing the plunger…
brown color intensified because of the sudden compression of the gasmolecules
increase in gas pressure by sudden decrease in volume increases theconcentrations of both NO2 and N2O4 to the same degree thus the browncolor intensified
after few seconds, the color of the gas became light brown
when equilibrium has been reestablished, the resulting mixture is lighter incolor than the original
the rate of decomposition of N2O4 is not appreciably affected by change inits concentration upon the sudden compression but the rate of reaction of
NO2 molecules to form N2O4 is increased because it increased in number of molecules
Generalization: Increasing the pressure of the system by decreasing the volumeof container favors the reaction which produces the less number of molecules.On the other hand, decreasing the pressure by increasing the volume favors thereaction which increases the total number of molecules.
Reaction Quotient ()
similar to K but uses initial concentration
if Q < , the equilibrium shifts forward
if Q > , the equilibrium shifts backward
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if Q = K, there is no shift and the system is at equilibrium
Electrolytes are substances whose solutions in a given liquid contain positiveand negative ions regardless whether these ions existed in the pure solute or were formed in the process of solutions and are capable of conducting electricity.
Non-electrolytes are solutes whose solutions in a given liquid containmolecules and thus are non-conductors of electricity.
Covalent electrolytes are compounds which are not ionic but behave liketypical electrolytes when dissolved in water; thus they give solutions that containions.
Weak electrolytes do not dissociate completely in a solution while strongelectrolytes dissociate completely in a solution.
Strong acids; like HCl, H2SO4, HClO4, HI, HBr, and HNO3; and strong bases,which includes all hydroxides of Group 1 and 2 elements, are also strongelectrolytes.
Brønsted-Lowry acids and bases identify acids (a proton donor) and bases(proton acceptor) and their corresponding conjugate base and conjugate acid ina dissolution process.
Calculations of pH of strong and weak acids and bases
pH = − logH3O+
H
3O+
= 10−pH
pOH = − logOH− OH− = 10−pOH
pH + pOH = 14
A buffer solution is a solution whose pH remains almost constant despitedilution or addition of small amounts of either an acid or a base
After the dissociation of a weak acid/base into water, a conjugate base/acidand a conjugate acid/base will be formed. If a weak acid is dissociated into water,the ion from the acid becomes a conjugate base while water becomes hydronium
and a conjugate acid.If an acid is added to the (acid) buffer solution, the conjugate base neutralizes
it.If a base is added to the (acid) buffer solution, the acid neutralizes it.
Radioactivity is a phenomenon in which an unstable nuclei spontaneouslyemits various particles and/or electromagnetic radiation.
Rules in balancing chemical reactions:
the total number of nucleons in the products must be equal as that in thereactants
the total number of nuclear charges in the products and the reactants must bethe same
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Types of radioactive decay:
alpha emission involves the emission of a He24 or an α particle from an
unstable nucleus, resulting in a daughter nuclide with a mass number four lessand atomic number two less than the parent nuclide: XZA → JZ−2
A−4 + He24
beta (electron) emission is the emission of a high speed electron from anunstable nucleus and can be thought of as the conversion of a neutron to a
proton and electron with the emission of the electron: n01 → H1
1 + e−11
positron emission results in a daughter nuclide that has the same mass
number, but an atomic number one less than the parent nuclide: p11 → n0
1 + e10
electron capture occurs when an unstable nucleus captures an electron from
a core atomic orbital of an atom: p11 + e−1
1 → n01 + γ
gamma emission results from the loss of energy from an excited state of a
nucleus: XZA
→XZ
A +
γ
Rate of radioactive decay:The half-life for a radioactive decay is given by ln 2 over the decay constant, .
12
=ln 2
The relationship between the fraction of radioactive nuclei, 0, and time, , is
given by:
ln 0
= −