chapter 4 Flashcards
what is a reaction? what is used to represent them?
• A reaction is chemical changes in matter that results in
new substances
• A chemical equation is used to describe the reaction
what does the law of conservation of mass state?
From the Law of Conservation of Mass in a chemical
reaction, matter is neither created nor destroyed
can subscripts change? what must be included?
• Subscripts of atoms cannot change
• Must include subscripts to indicate the phase of the
chemical ie. (s), (l), (g), (aq)
what are coefficients used for?
Coefficients are used to balance the equation, but also
indicate the relative amounts required for a complete
reaction from reactants to product
what are the energy symbols?
! Δ = heat
! hν = light
!shock = mechanical
!elec = electrical
what do the coefficients specify?
The coefficients in a balanced chemical reaction specify
the relative amounts in moles of each of the substances
involved in the reaction
what are reaction stoichiometries?
• The numerical relationship between chemical amounts in
balanced reactions are the reaction stoichiometries
why do we need stoich?
• Cannot directly convert mass of reactants to mass of
products
what do stoichiometric ratios apply to?
• Stoichiometric ratios only apply to the molar ratios of
compounds
• Need to convert amounts into moles in order to predict
moles of product, which can then be converted to mass
why do we have limiting reagents?
• In the real world we don’t generally have exact
stoichiometric amounts of all reactants
• In addition, reactions rarely proceed with 100%
efficiency
what can we use to determine LR?
Based on the moles of starting material we can
determine the limiting reagent
How can we determine theoretical yield?
• Using stoichiometric ratios we can determine a
theoretical yield if the reaction goes to 100% completion
how can we determine percent yield?
Given the actual product amounts we can calculate the
percent yield
when do we have to determine the LR? what does the LR determine?
When we don’t have actual stoichiometric amounts of
reactants we need to determine the limiting reagent
• The limiting reagent determines the maximum amount of
product that can be formed
• To determine the limiting reagent compare the actual
ratio of reactants present to the stoichiometric ratio
found in the balanced equation
what is a homogeneous mixture? two parts of a solution?
• A homogenous mixture of two substances is known as a
solution
• A solution is made up of two parts: solvent and solute
• When a substance is mixed in water it is called an
aqueous solution (aq)v
what is the solvent?
• Solvent is the component
found in larger quantities
(water in aqueous solutions)
what is the solute?
Solute is the compound
found in smaller quantities
what happens when a solute dissolves in a solvent?
There are two competing interactions in a mixture:
solvent-solute and solute-solute
• When a solute dissolves in a solvent the solvent-solute
attractive forces are stronger than the solute-solute
interactions
how are electrolytes used?
In sports drinks they replace essential salts/ions we lose
through sweat
• For industrial applications they conduct electricity
• There must something in solution that allows the charge
to pass through from one electrode to the other
what do electrolyte solutions contain?
Electrolyte solutions contain dissociated ions
• Strong electrolytes contain fully dissociated ions (NaCl),
while weak electrolytes contain partially dissociated ions
what are solids that dissolve but do not dissociate called?
Solids that dissolve, but do not dissociate into ions are
called nonelectrolytes
sugar, molecular compounds
are ionic salts soluble?
Not all ionic solids (salts) are soluble in water
• There is no easy way to predict whether a solid will be
soluble or not
polyatomic ions?
When polyatomic ions dissolve they remain as intact
units
• Solubility exists on a continuum rather than an absolute
value
6 solubility rules
1. All salts containing cations of group 1 metals (alkali metals, Li+, Na+, K+, etc.) and ammonium ions (NH4 \+) are soluble. 2. All nitrates (NO3 - ), ethanoates (acetates, CH3COO-), chlorates (ClO3 - ), and perchlorates (ClO4 - ) are soluble. 3.Salts containing Ag+, Pb2+, and Hg2+ are insoluble. 4. Most chlorides (Cl- ), bromides (Br- ), and iodides (I- ) are soluble. 5. Sulphates (SO4 2-) are soluble, except those containing Ca2+, Sr2+, Ba2+. 6. Carbonates (CO3 2-), hydroxides (OH- ), oxides (O2-), phosphates (PO4 3-), and sulphides (S2-) are generally insoluble.
look at solubility tables
ok
what are compounds on the data table list?
Simply know
for now that if a compound
appears on this list, it is
insoluble.
what are the two main types of inorganic reactions that take place in aqueous media?
! Metathesis
! Oxidation-Reduction (redox)
what are metathesis reactions?
Metathesis reactions are double replacement reactions
where the cations and anions of the reactants are
swapped
✓ AB + CD → AD + BC
✓ Driving force is the production of a precipitate or
formation of an unionized molecular compound (gas,
water, weak acid)
when do precipitation reactions occur?
Precipitation reactions occur when we mix two solutions
together and a solid (precipitate) forms.
A precipitate will form only from insoluble compounds
Must determine which species are present in solution
and if any combination forms an insoluble compound
how do we write molecular reactions? (precipitation)
shows the complete neutral formulas for each
compound as if they existed as molecules
how do we write complete ionic reactions? (precipitation)
“lists all of the ions and species present in either
reactants or products
how do we write net ionic reactions? (precipitation)
“shows only the reactant ions and products that take
part in the precipitation reaction
what does a net ionic equation include?
• Ions that do not take part in the precipitation reaction are
called spectator ions
• The net ionic equation includes only the ions in solution
that react to form the insoluble precipitate
Describe Arrhenius
Acids produce H+ in aqueous solutions
• Bases produce OH-
in aqueous solutions
describe bronsted-lowry
- Acids are proton donors
* Bases are proton acceptors
describe lewis acid base
Acids are e-
pair acceptors
• Bases are e-
pair donors
what is an acid base reaction also called?
An acid-base reaction is also called a neutralization
reaction
Protons associate with water molecules to form
hydronium ions H3O+
• Can be used interchangeably with H+
what are strong acids and bases?
Acids and bases that 100% dissociate into ions are
called strong acids and strong bases
what are weak acids and bases?
Acids and bases that do not completely dissociate into
the respective ions are called weak acids and weak
bases
what are polyprotic acids?
Acids with more than one ionizable proton are polyprotic
acids
• Diprotic acids contain 2 ionizable protons
Can get analogous case with bases as well with X(OH)2
formula that can dissociate to give two OH-
(aq) ions
strong acids and bases to remember
HCl LiOH
HBr NaOH
HI KOH
HClO4 RbOH
HNO3 CsOH
H2SO4 Ca(OH)2
Sr(OH)2
Ba(OH)2net ionic for neutralizations
H+(aq) + OH−(aq) → H2O
what do an acid and a base produce?
acid + base → salt + water
metal or hydrogen carbonates
Metal carbonates or hydrogen carbonates: React with
strong acids to produce carbonic acid, which degrades
into CO2(g) and H2O(l)
metal and hydrogen sulphites
React with
strong acids to produce sulphurous acid, which
decomposes to give SO2(g) and H2O(l)
metal sulphites
Metal sulphides: React with strong acids to produce
H2S(g) and a salt
ammonium salts
: React with a strong base to form
ammonia and water
what is the chemical event that occurs in redox?
The chemical event that occurs in a oxidation-reduction
(redox) reaction is the net movement of electrons from
one reactant to another
what happens with redox of ionic compounds?
Ionic compounds transfer electrons
what happens with molecular compounds?
Molecular compounds shift electrons
what is oxidation? reduction?
Oxidation is the loss of electrons
!Reduction is the gain of electrons
what are the oxidizing and reducing agents?
The oxidizing agent (O.A) causes the oxidation of the
other species
• The reducing agent (R.A) causes the reduction of the
other species. Therefore:
✓ The O.A. is reduced
✓ The R.A. is oxidized
what can we use to remember redox reactions?
OIL RIG
LEO the lion goes GER
how do we know if redox has occurred?
OXIDATION NUMBER
• The oxidation number of an atom in a compound is the
charge it would have if shared electrons were assigned
to atoms with the greatest attraction for electrons
what is the oxidation number in binary ionic compounds?
In binary ionic compounds the oxidation number is the
same as the ionic charge
rules for oxidation numbers of elements and mono atomics
- Atoms in elemental form have an oxidation number of
zero (0)
• Cl2, O2 - The oxidation number of a monoatomic ion is equal to
the ion’s charge
• Fe2+, Ca2+
rules for oxidation numbers of neutral compounds, polyatomics, and metals in compounds
The sum of the oxidation numbers of all atoms in:
• a neutral molecule is always 0
• H2O, HCl
• a polyatomic ion is always equal to the charge of
the ion
• SO3
2-, NO3
-
4. In their compounds, metals always have positive
oxidation states:
• Group 1 metals always have a +1 oxidation number
• Group 2 metals always have a +2 oxidation number
oxidation numbers for hydrogen and nonmetals in compounds
- The oxidation state of hydrogen in a compound is
usually +1 - In their compounds, the nonmetals typically have
negative oxidation states:
• Fluorine always has an oxidation number of -1
• Other Group 17 elements usually have an oxidation
number of -1
• Oxygen usually has an oxidation number of -2
• Other Group 16 elements usually have an oxidation
number of -2
• Group 15 elements usually have an oxidation number
of -3
what happens with elements that aren’t covered by these rules?
Some elements are not covered by these rules
• Need to determine the oxidation numbers of elements
covered by the list and then use Rule 3 to determine the
oxidation number of the remaining elements
• Rules higher up on the list take precedence over rules
lower down the list
can compounds have multiple oxidation numbers?
yes, The oxidation state of a particular element is dependent on the other atoms bonded to it
how can we tell if an atom has oxidized? reduced?
If an atom has a higher (more positive) oxidation number
in the products than it had in the reactants, then the
reactant that contains that atom was oxidized
• If an atom has a lower (more negative) oxidation number
in the products than it had in the reactants then the
reactant that contains that atom was reduced
summary
Oxidation Reduction Loses e- Gains eReducing agent Oxidizing agent Increased O.N. Decreased O.N.
what does molarity describe? formula?
We use the term molarity to describe the amount of
solute present in 1 litre of solution
• Molarity: M (mol/L)
• M = n/V, where n = the number of moles of solute
how is molarity used in calculations?
Molarity of a solution shows the relationship between
the amount of solute (in moles) and the solvent (in litres)
• If a salt solution is 2M, then 1 litre of water contains 2
moles of salt
!4L = 8 moles
ex How many moles of KCl are there in 0.65 L of a 1.5M KCl solution? L solution mol KCl 1.5 mol KCl 1 L 0.65 L × 1.5 mol KCl 1 L = 0.98 mol KCl
how do we dilute a solution? formulas?
In the laboratory, solutions are often stored as stock
solutions
• To make solutions of lower concentration we add more
solvent
! The amount of solute doesn’t change, only the
volume
!moles of solute in solution 1 = moles of solute in
solution 2
M1V1 = M2V2 C1V1 = C2V2
