CHEM103 / CHEM 103 Module 2 Exam
Questions & Answers | Latest 2026–2027
Update | General Chemistry I with Lab |
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Grade A
2026 / 2027 Academic Year
Q: Water in solid state
Answer
Move fast, stay vlose together but dont touch
Q: When water is heated it clumps
Answer
Together more
Q: When water is heated above boiling it
Answer
Moves far apart and moves very fast
Q: Solid
Answer
Close together in clump in center
Q: Liquid
Answer
Fill bottom of container
Q: Gas
Answer
Move all around container
Q: When water is cooled the molecules
Answer
Only wiggle and not spin
Q: Gas:
Answer
Molecules are far apart and move a lot
Q: Neon and argon are
Answer
More dense in solid form
Q: Water is weird because
Answer - it's solid form is less dense than it's liquid from - all 3 states are found at naturally occurring temps on earth
Q: Physical change
Answer
No bonds are broken or formed. The same substance is there after the change.
Q: Chemical change
Answer
The bonds break apart and the atoms rearrange into new substances with new chemical
bonds
Q: K
Answer
Element symbol
Q: Ag
Answer
Element symbol
Q: 208
Answer
PB
82. The 208 is the
Mass number
Q: Mass number =
Answer
Protons + electrons
Q: 208
Answer
Pb
82. The 82 is
Atomic number (z)
Q: The atomic number is
Answer
# of protons in an atom
Q: The mass of a proton is
Answer
1 amu
Q: The mass of a neutron is
Answer
1 amu
Q: The mass of an electron is
Answer
.0005amu
Q: 1.6605x10^-27 is
Answer
1 anu
Q: The diameter of an atom is
Answer
2 Å
Q: Each letter is
Answer
100 atoms
Q: Daltons atomic model (1800)
Answer
Elements are made of extremely small particles called atoms
Q: Thompson's atomic model (1900)
Answer
Plum-pudding model
Q: Rutherford's Atomic Model (1910)
Answer - atoms tiny combine at the center of the volume - most particles pass through unaffected
Q: > 99.9% probability that all
Answer
Particles pass
Only alpha particles that directly hit the nucleus are
Answer
Backscattered
Radius of an atom=
Answer
20,000X radius of a nucleus
In mass spectrometry: if two particles have the same charge the lighter particles are
Answer
Deflected more
In mass spectrometry: if two particles have the same charge the heavier particles are
Answer
Deflected less
Soft-ionization mass spectrometry:
Answer
All covalent bonds remain intact
Molecular compounds
Answer
Usually formed by combination of non metals with metals
Ionic compounds
Answer
Typically formed by combination of reactive metals with reactive non-metals
Ionic compounds consist of
Answer
Ions packed in a crystal lattice
Like charges
Answer
Repel
Unlike charges
Answer
Attract
Coulomb's Law
Answer
F=K q₁*q₂/r², magnitude of force between two charges
Work=
Answer
Force X distance
Potential energy = u =
Answer
Constant X Q1xQ2/d
U>0
Answer
Repulsive
U<0
Answer
Attractive
Magnitude of u increases with - more charge - smaller separation - greater magnitude of u
Pure substance - constant composition - element compound - Ex: He, H2O, H2
Mixture - combination of pure substances - variable composition -Ex: N2+ O2, salt water
You cannot change the ________ of a pure substance, once you change it, it becomes a
___________
Composition, mixture
Pure substances can be changed by
"Chemical"
Mixtures can be changed by
"Physical"
Electrolysis is a chemical process that
Can break done into it's pure elements
Homogeneous mixture - indistinguishable parts - Ex: salt water, brass, air - most alloys are in this category
Heterogenous mixture - multiple distinguishable parts - composition can vary and be seen - Ex: water and soil, sand and water
Vaporization
Liquid to gas
Condensation
Gas to liquid
Sublimation
solid to gas
Deposition
gas to solid
Solids - definite shape - definite volume - high density - slightly compressible
Liquids - no definite shape - definite volume - mid-high density - slightly compressible
Gases - no definite shape - no definite volbume - low density - highly compressible
Matter
Anything that has mass and takes up space
Matter is made from
Atoms
solid to liquid
melting
Liquid to gas
vaporization
Solid to gas
sublimation
Liquid to solid
freezing
Gas to liquid
condensation
Gas to solid
deposition
melting, vaporization, sublimation
endothermic
freezing, condensation, deposition
exothermic
Plasma is
Ionized gas
Gas + heat =
Plasma
The process of going from gas to plasma is known as
Ionization
The reverse process of ionization is
Recombination
Gas in its neutral state does not conduct electricity, plasma
Does conduct electricity
Plasma is present in
Sun, neon signs, fire, lightning
Does not change chemical identity
Physical property
Ex. Boiling point
Physical property
Ductility
Physical property
Malleability
Physical property
Color
Physical property
Viscosity
Physical property
Mass, weight
Physical property
Volume
Physical property
Does change chemical identity
Chemical property
Flammability
Chemical property
Corrosive
Chemical property
Combustible
Chemical property
Explosive
Chemical property
Color changing
Chemical property
pH
Chemical property
Taste
Chemical property
Rutherfords conclusions of atoms - the atom must be mostly empty space - there must be a very dense center (nucleus) - at the center there is a region of dense positive charge
2.1: MOLECULAR WEIGHT
A compound is made up of two or more elements combined in a definite ratio that is
represented by a molecular formula. Each of these elements has a certain atomic weight,
which can be found in the periodic table. The sum of the atomic weights of the atoms in the
molecular formula is called the formula weight or molecular weight or formula mass.
Ca3(PO4)2
calcium phosphate
Molecular Weight =
3 Ca= 3 x 40.08=120.24
2 P=2 x 30.97=61.94
8 O=8 x 16.00=128.00
Total 310.18
2.2: MOLES
Chemical compounds react with one another in amounts that are based on their molecular
weights; this chemically reactive amount of compound is called a mole.
moles
= grams / molecular weight
Calculate the number of moles in 10.0 grams of each of the following compounds:
Ca3(PO4)2 10.0 g ÷ 310.18 = 0.0322 mol (3 sig fig because of 10.0 g)
C3H5O2Cl 10.0 g ÷ 108.52 = 0.0921 mol
Al2(SO4)3 10.0 g ÷ 342.17 = 0.0292 mol
Ca3(PO4)2 0.0500 mol x 310.18 = 15.5 g
C3H5O2Cl 0.0500 mol x 108.52 = 5.43 g
Al2(SO4)3 0.0500 mol x 342.17 = 17.1 g
2.3: PERCENT COMPOSITION
he molecular formula represents the definite ratio of elements in a compound. The weight
of each element present in the compound represents a certain percentage of the total weight
of the compound. The percentage of each element present in a compound is called the %
composition of the compound.
The percentage of an element present in a compound can be calculated as shown below:
% of an element = weight of element / molecular weight of compound x 100
Ca3(PO4)2
3 Ca = 3 x 40.08= 120.24
2 P = 2 x 30.97= 61.94
8 O = 8 x 16.00 = 128.00
310.18
% Ca = (120.24 ÷ 310.18) x 100 = 38.76%
%P = (61.94 ÷ 310.18) x 100 = 19.97%
%O = (128.00 ÷ 310.18) x 100 = 41.27%
2.4: EMPIRICAL FORMULA
If the formula of a compound is known, the % composition of the compound can be
determined. This process can be done in reverse: The formula of the compound can be
determined if the % of each element present in the compound is known. The formula
calculated from % composition is known as the empirical formula (or the simplest formula).
The actual molecular formula is some multiple of this simplest formula, which is
determined by knowing the molecular weight.
To determine the empirical formula:
(1) Divide each element % by its exact atomic weight to give a set of numbers.
(2) Divide the smallest of this set of decimal numbers into each of the numbers (including
itself) to yield a second set of numbers.
(3a) Round off each of the second set of decimal numbers to a whole number.
OR
(3b) If the numbers derived from the division in step 2 are recognized as exact decimal
equivalents of fractions (such as n.25 = 1/4, n.333 = 1/3, n.5 = 1/2, n.666 = 2/3, n.75 =
3/4), multiply all of the numbers derived by division by the denominator of the recognized
fraction to give whole numbers.
(4) Each whole number is the number of atoms of that element in the empirical formula.
% Composition of a compound is:
32.37% Na; 32.37% Na ÷ 22.99 = 1.408
22.58%S; 22.58% S ÷ 32.07 = 0.704 (smallest number of the set)
45.05% O; 45.05% O ÷ 16.00 = 2.816
0.704 is the smallest of this set of numbers, so it is divided into each of the set of numbers.
Na = 1.408 ÷ 0.704 = 2 Na
S = 0.704 ÷ 0.704 = 1 S
O = 2.816 ÷ 0.704 = 4 O
Na2SO4
2.5: BALANCING CHEMICAL EQUATIONS
When certain chemical materials are added to one another, they undergo a chemical
reaction in which the atoms of the materials separate from one another and recombine in a
new way to form new materials. This chemical reaction can be described by a chemical
reaction equation in which the reactants (starting materials) are written on the left side of
the equation and the products (final materials) are written on the right side of the equation,
separated by an arrow which points from left to right (some sites use an equals sign here
but this is incorrect because the only thing equal about this equation is the number of
atoms, once balanced), an example of which is shown below:
NaOH + HCl → NaCl + H2O
The reaction equation is read as follows:
Sodium hydroxide + Hydrochloric acid YIELDS Sodium chloride + Water
To balance a reaction equation, numbers (called coefficients) may be placed in front of each
formula, but the subscript numbers indicating how many atoms of each element are in each
formula may not be changed
Original equation: Al(OH)3 + H2SO4 → Al2(SO4)3 + H2O
NOTICE: The Al, O, H, and S atoms are not equal on each side of the equation. The
equation is unbalanced (1 Al on left, 2 Al on right, etc).
Balanced equation: 2 Al(OH)3 + 3 H2SO4 → Al2(SO4)3 + 6 H2O
NOTICE: There are 2 Al, 18 O, 12 H, and 3 S atoms on each side of the equation. The
equation is balanced.
Now let's balance another equation:
Original equation: Al4C3 + H2O → Al(OH)3 + CH4
Al4C3 + H2O → Al(OH)3 + CH4 (original equation)
Al4C3 + H2O → 4 Al(OH)3 + CH4 (to balance Al)
Al4C3 + H2O → 4 Al(OH)3 + 3 CH4 (to balance C)
Al4C3 + 12 H2O → 4 Al(OH)3 + 3 CH4 (to balance H and O)
2.6: TYPES OF REACTIONS - 5 types
Molecular and Ionic Equations
For a reaction involving ionic materials, we can write the reaction equation in different
ways depending on what information we want to express. We can write the equation as a
molecular equation, an ionic equation, or a net ionic equation:
In a molecular equation the substances are written as molecular substances even though
they may actually exist in solution as ions. A molecular equation is shown below:
CaCO3 + 2 HCl → CaCl2 + CO2 + H2O
You could also write this as an ionic equation, which tells what is actually happening at the
ionic level in a solution. An ionic equation is shown below:
Ca+2, CO3-2 + 2 H+, 2 Cl- → Ca+2, 2 Cl- + CO2 + H2O
You could also write this as a net ionic equation, which shows the actual reaction that
occurs at the ionic level. In this net ionic equation, spectator ions (ions that appear on both
sides of the equation in the same form) are canceled out to yield the net ionic equation.
CO3-2 + 2 H+ → CO2 + H2O
1) Combination or Synthesis Reactions
A reaction in which a single product is formed from multiple reactants
2 Na + Cl2 → 2 NaCl
2 H2 + O2 → 2 H2O
2) Decomposition Reactions
A reaction in which a single reactant is converted to multiple products
CaCO3 → CaO + CO2
Mg(OH)2 → MgO + H2O
4) Double Replacement Reactions
A reaction in which two ionic compounds exchange their ions to form a non-ionic
(molecular) compound product as (1) a solid insoluble precipitate, (2) a gas, or (3) a
3) Combustion Reactions
A reaction in which hydrocarbon (compound containing only carbon and hydrogen) or
C,H,O compound is reacted with elemental oxygen (O2) to form carbon dioxide and water
2 C4H10 + 13 O2 → 8 CO2 + 10 H2O
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
molecular compound, the formation of which drives the reaction to completion.
(1) Ba+2(NO3-1)2 + (K+)2SO4 → BaSO4 ↓ + 2 (K+),(NO3-1) (precipitate)
(2) Ca+2 CO3-2 + 2 H+Cl- → Ca+2(Cl-)2 + CO2 ↑ + H2O (gas)
(3) Ca+2(OH-1)2 + 2 H+Cl- → Ca+2(Cl-)2 + H2O
(molecular)
5) Single Replacement Reaction
A reaction in which a (1) metallic element reacts with an ionic compound to replace the
metal ion from the ionic compound as a metal element or a reaction in which a (2)
nonmetal element reacts with an ionic compound to replace the nonmetal ion as a
nonmetal element. One of the materials gains electrons (undergoing reduction) as one of
the other materials loses electrons (undergoing oxidation).
1) Zn + Cu+2, SO4-2 → Zn+2, So4-2 + Cu
2) 2K+1, 2Br-1 + Cl2 → 2K+1, 2Cl-1 + Br2
Type #4 - Predicting Precipitation Reactions by Using the Solubility Rules
How do we know when a precipitation reaction will occur to form an insoluble precipitate
rather than the reaction just forming a mixture of the four ions? This is based on a set of
rules known as solubility rules, which allows you to predict when a reaction will occur
between two ions to form an insoluble molecular precipitate. This set of solubility rules is as
follows:
Compounds that are mostly insoluble in water are:
Compounds containing the S-2 (sulfide) ion: exceptions are NH4+ (ammonium) and group
I and II sulfides
Compounds containing the OH-1 (hydroxide) ion: exceptions are NH4+ and group I
hydroxides
Compounds containing the CO3-2 (carbonate) ion: exceptions are NH4+ and group I
carbonates
Compounds containing the PO4-3 (phosphate) ion: exceptions are NH4+ and group I
phosphates
Compounds that are mostly soluble in water are:
Compounds containing the NH4+ and group I and II ions
Compounds containing the NO3-1 (nitrate) and C2H3O2-1 (acetate) ions
Compounds containing the Cl-1 (chloride), Br-1 (bromide) or I-1 (iodide) ions: exceptions
are Ag+, Pb+2, and Hg2+2 compounds
Compounds containing the SO4-2 ion: exceptions are Sr+2, Pb+2, Ba+2, and Hg2+2
compounds
DOUBLE DISPLACEMENT PRECIPITATION REACTIONS
Mg+2, SO4-2 + 2 Na+1, 2 OH-1 → Mg(OH)2 ↓ + 2 Na+1, SO4-2
Ni+2, Cl-1 + Na+1, Br-1 → Will not occur since neither set of ions forms a precipitate
Ag+1, NO3-1 + Na+1, I-1 → AgI ↓ + Na+1, NO3-1
Ca+2, Cl2-1 + Al+3, 3 NO3-1 → Will not occur since neither set of ions forms a precipitate
Pb+2, 2 NO3-1 + 2 Na+1, 2 Br-1 → PbBr2 ↓ + 2 Na+1, 2 NO3-1
2.7: TYPES OF REACTIONS II
A single replacement reaction occurs when:
1. a metallic element reacts with an ionic compound to replace the metal ion from the ionic
compound as a metal element, or
2. a nonmetal element reacts with an ionic compound to replace the nonmetal ion as a
nonmetal element.
This is another reaction in which a molecular material (the metal or nonmetal element) is
formed as a product as in the double replacement reactions. This single replacement
reaction is one example of a very prevalent type of reaction know as an oxidation-reduction
(or redox) reaction in which electrons are transferred to cause oxidation number changes.
One of the materials will gain electrons (undergoing reduction) as one of the other
materials loses electrons (undergoing oxidation).
(1) Zn + Cu+2, SO4-2 → Zn+2, SO4-2 + Cu
(2) 2 K+1,2 Br-1 + Cl2 → 2 K+1, 2 Cl-1 + Br2
Predicting Single Replacement Reactions by Using the Activity Series
How do we know whether a single replacement reaction will occur to form a metal or
nonmetal element? This is based on set reactivity rules that allow you to predict that a
reaction will occur between a metal and a metal ion or a nonmetal and a nonmetal ion. This
set of predictors is known as the metal and nonmetal activity series and is shown below.
Any element (Metal 1) higher on the metal activity series is more likely to react with an ion
of a metal (Metal 2) lower on the activity series to form an ion of Metal 1 and the element of
Metal 2. Any element (Nonmetal 1) higher on the nonmetal activity series is more likely to
react with an ion of a nonmetal (Nonmetal 2) lower on the activity series to form an ion of
Nonmetal 1 and the element of Nonmetal 2.
Metal Activity Series - (Reaction #5)
Li-Most Acitve; Likely to lose electron+ion
K
Ba
Ca
Na
Mg
Al
Mn
Zn
Cr
Fe
Co
Ni
Sn
Pb
H2
Cu
Ag
Hg
Pt
Au (Least active)
Nonmetal Activity Series
F2 (most active gain electron - ion)
Cl2
Br2
I2 (least active)
Will the following reaction occur?
2 K + Pb+2 → 2 K+ + Pb
K is higher on the metal activity series table than Pb, which tells us that K forms a positive
ion more easily than Pb; therefore, if K reacts with Pb+2, the following two half-reactions
will take place to cause the following reaction:
2 (K → K+ + e-)
Pb+2 + 2e- → Pb
2 K + Pb+2 → 2 K+ + Pb
Will the following reaction occur?
Au + Mg+2 → Au+2 + Mg
Mg is higher on the metal activity series table than Au, which tells us that Mg forms a
positive ion more easily than Au; therefore, if Au reacts with Mg+2, the reaction proposed
above will not take place because Mg+2 is already present as the ion and will remain in that
form.
Will the following reaction occur?
F2 + 2 Br-1 → 2 F-1 + Br2
F2 is higher on the nonmetal activity series table than Br2, which tells us that F forms a
negative ion more easily than Br; therefore, if F is reacted with Br-1, the following two half
reactions will take place to cause the following reaction:
2 (Br-1 → Br2 + e-)
F2 + 2e- → 2 F-
↓
F2 + 2 Br-1 → 2 F-1 + Br2
SINGLE DISPLACEMENT REACTIONS
Br2 + 2 I-1 → I2 + 2 Br-1 Will occur since Br2 is more active than I2
Cu + Sn+2 → Will not occur since Sn is more active than Cu
Cl2 + 2 F-1 → Will not occur since F2 is more active than Cl2 (???)
Ba + Fe+2 → Fe + Ba+2 Will occur since Ba is more active than Fe
TYPES OF REACTIONS
1. C5H12 + 8 O2 → 5 CO2 + 6 H2O Combustion
2. Mg + 2 HCl → MgCl2 + H2 Single Replacement
3. H2 + Cl2 → 2 HCl Combination
4. 2 KClO3 → 2 KCl + 3 O2 Decomposition
5. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O Combustion
6. FeS + 2 HCl → H2S + FeCl2 Double Replacement
7. HCl + NaOH → NaCl + H2O Double Replacement
8. Al + Fe(NO3)3 → Fe + Al(NO3)3 Single Replacement
9. 2 S + 3 O2 → 2 SO3 Combination
10. H2SO4 → SO3 + H2O Decomposition
2.8: BALANCING REDOX EQUATIONS
There is a special type of chemical reaction equation known as a redox reaction. In this type
of equation, two of the atoms in the compounds undergo changes in their charges: The
charge of one of the atoms increases, and the charge of the other decreases. An increase in
charge occurs when that element loses one or more electrons, a process called oxidation. A
decrease in charge occurs when that element gains one or more electrons, a process called
reduction. In this reaction, all electrons lost by the one element must be gained by the other
atom.
2.8: BALANCING REDOX EQUATIONS; Rules for oxidation numbers
1. The sum of all the total charges in a compound is equal to zero (0).
2. The charge of an element is zero (0) (an element is an atom that is not combined with
any other element).
3. The normal charge of H is +1.
4. The normal charge of O is –2.
5. The charge of a group I, II, or III metal atom is positive (+) and equal to its periodic table
group number. (K = +1, Ca = +2, Al = +3)
6. The charge of any other (not in group I, II, or III) metal atom (in the center of the table)
cannot be determined from its periodic table position since it has no group number. We can
determine the charge of this atom by knowing the total charges of the other atoms (or
polyatomic groups) with which it is combined and using rule #1.
(Mn = +7 in KMnO4) since K = +1, 4 O = (4 x -2) so Mn = + 7 for sum of charges = 0
[Cr = +3 in Cr(NO3)3] since 3 NO3 = (3 x -1) so Cr = +3 for sum = 0
7. The charge of a nonmetal (which is combined only with a metal) is negative and equal to
(its Group Number – 8). (S = -2 in Na2S)
8. The charge of any other nonmetal is determined by knowing the total charges of the
other atoms with which it is combined and using rule #1 (N = + 5 in KNO3) sinceK = +1, 3
O = (3 x -2) so N = +5 for sum of charges = 0
Balancing redox equations should be done in this three-step process:
1. Determine the charge of each atom (including those that are part of polyatomic groups)
and determine which two atoms' charges are changing and what the changes are.
2. Equate the changes. Multiply the changes by numbers to produce two products (results of
each multiplications) that are equal. The numbers by which the changes were multiplied
become the coefficients of the compounds containing the changing atoms (on both sides of
the equation).
3. Balance the remainder of the atoms in the equation by making use of the coefficients
determined in step #2.
In some redox equations, one of the changing atoms is polyatomic, such as Cl2, Br2, C2O4
2, Cr2O7-2. In these cases, as shown below, the change of that atom must be doubled (or
tripled, etc.) before equating the changes.
FeCl2 + K2Cr2O7 + HCl → FeCl3 + CrCl3 + KCl + H2O
FeCl2: Each Cl is nonmetal in group VII = -1 (total = -2), so Fe = +2.
FeCl3: Each Cl is nonmetal in group VII = -1 (total = -3), so Fe = +3.
K2Cr2O7: K group I metal = +1 (total = +2), each O is -2 (total = -14), so Cr total is +12;
each Cr is +6.
CrCl3: Each Cl is nonmetal in group VII = -1 (total = -3), so Cr = +3.
Since Fe (on left side) is +2 and Fe (on right side) is +3, Fe changes by 1.
Since each Cr (on left side) is +6 and Cr (on right side) is +3, Cr changes by 3 x 2 (since
Cr2O7-2) = 6.
Multiply Fe compounds by 6 and Cr2O7-2 compound by 1, and, after balancing other atoms
(which requires placing a 2 in front of CrCl3) =
6 FeCl2 + 1 K2Cr2O7 + 14 HCl → 6 FeCl3 + 2 CrCl3 + 2 KCl + 7 H2O
This is an oxidation-reduction (redox) reaction:
6 FeII - 6 e- → 6 FeIII (oxidation)
2 CrVI + 6 e- → 2 CrIII (reduction)
FeCl2 is a reducing agent, K2Cr2O7 is an oxidizing agent.
Zn + KNO3 + HCl → ZnCl2 + KCl + NH4Cl + H2O
Zn + KNO3 + HCl → ZnCl2 + KCl + NH4Cl + H2O
Zn (on left side) is uncombined so Zn = 0
ZnCl2: each Cl is nonmetal in group VII = -1 (total = -2), so Zn = +2
KNO3: K is metal in group I = +1, each O is -2 (total is -6), so N is +5
NH4Cl: Cl is nonmetal in group VII = -1, each H is +1 (total is +4), so N is -3
Since Zn (on left side) is 0 and Zn (on right side) is +2: Zn changes by 2
Since N (on left side) is +5 and N (on right side) is -3: N changes by 8
Multiply Zn compounds by 4 and N compounds by 1 and after balancing other atoms =
4 Zn + 1 KNO3 + 10 HCl → 4 ZnCl2 + 1 KCl + 1 NH4Cl + 3 H2O
Mn(NO3)2 + NaBiO3 + HNO3 → HMnO4 + Bi(NO3)3 + NaNO3 + H2O
Mn(NO3)2: each NO3 is -1 (total is -2), so Mn is +2
HMnO4: H = +1, each O is -2 (total is -8), so Mn is +7
NaBiO3: Na is metal in group I = +1, each O is -2 (total is -6), so Bi is +5
Bi(NO3)3: each NO3 is -1 (total is -3), so Bi is +3
KMnO4 + KNO2 + HCl → MnCl2 + KCl + KNO3 + H2O
KMnO4 + KNO2 + HCl → MnCl2 + KCl + KNO3 + H2O
Since Mn (on left side) is +2 and Mn (on right side) is +7: Mn changes by 5
Since Bi (on left side) is +5 and Bi (on right side) is +3: N changes by 2
Multiply Mn compounds by 2 and Bi compounds by 5 and after balancing other atoms =
2 Mn(NO3)2 + 5 NaBiO3 + 16 HNO3 → 2 HMnO4 + 5 Bi(NO3)3 + 5 NaNO3 + 7 H2O
KMnO4: K is metal in group I = +1, each O is -2 (total is -8), so Mn is +7
MnCl2: each Cl is nonmetal in group VII = -1 (total = -2), so Mn = +2
KNO2: K is metal in group I = +1, each O is -2 (total is -4), so N is +3
KNO3: K is metal in group I = +1, each O is -2 (total is -6), so N is +5
Since Mn (on left side) is +7 and Mn (on right side) is +2: Mn changes by 5
Since N (on left side) is +3 and N (on right side) is +5: N changes by 2
Multiply Mn compounds by 2 and N compounds by 5 and after balancing other atoms =
2 KMnO4 + 5 KNO2 + 6 HCl → 2 MnCl2 + 2 KCl + 5 KNO3 + 3 H2O
Bi(OH)3 + Na2SnO2 → Bi + Na2SnO3 + H2O
Bi(OH)3: each OH is -1 (total is -3), so Bi is +3
Bi (on right side) is uncombined so Bi = 0
Na2SnO2: Na is metal in group I = +1 (total is +2), each O is -2 (total is -4), so Sn is +2
Na2SnO3: Na is metal in group I = +1 (total is +2), each O is -2 (total is -6), so Sn is +4
Since Bi (on left side) is +3 and Bi (on right side) is 0: Bi changes by 3
Since Sn (on left side) is +2 and Sn (on right side) is +4: N changes by 2
Multiply Bi compounds by 2 and Sn compounds by 3 and after balancing other atoms =
2 Bi(OH)3 + 3 Na2SnO2 → 2 Bi + 3 Na2SnO3 + 3 H2O
NaCrO2 + NaClO + NaOH → Na2CrO4 + NaCl + H2O
NaCrO2: Na is metal in group I = +1, each O is -2 (total is -4), so Cr is +3
Na2CrO4: Na is metal in group I = +1 (total is +2), each O is -2 (total is -8), so Cr is +6
NaClO: Na is metal in group I = +1, each O is -2, so Cl is +1
NaCl: Na is metal in group I = +1, so Cl is -1
Since Cr (on left side) is +3 and Cr (on right side) is +6: Cr changes by 3
Since Cl (on left side) is +1 and Cl (on right side) is -1: Cl changes by 2
Multiply Cr compounds by 2 and Cl compounds by 3 and after balancing other atoms =
2 NaCrO2 + 3 NaClO + 2 NaOH → 2 Na2CrO4 + 3 NaCl + H2O
Since each C (on left side) is +3 and C (on right side) is +4: C changes by 1 x 2 (since
H2C2O4) = 2
KMnO4 + H2C2O4 + H2SO4 → MnSO4 + K2SO4 + CO2 + H2O
KMnO4: K group I metal = +1, each O is -2 (total = -8), so Mn = +7
MnSO4: each SO4 is -2, so Mn is +2
H2C2O4: each H = +1 (total = +2), each O is -2 (total = -8), so C total is +6, each C is +3
CO2: each O is -2 (total = -4), so C is +4
Since Mn (on left side) is +7 and Mn (on right side) is +2: Mn changes by 5
Multiply Mn compounds by 2 and H2C2O4 compound by 5 and after balancing other atoms
(which requires placing a 10 in front of CO2) =
2 KMnO4 + 5 H2C2O4 + 3 H2SO4 → 2 MnSO4 + K2SO4 + 10 CO2 + 8 H2O
This is an oxidation-reduction (redox) reaction:
2 MnVII + 10 e- → 2 MnII (reduction)
10 CIII - 10 e- → 10 CIV (oxidation)
KMnO4 is an oxidizing agent, H2C2O4 is a reducing agent.
2.9: EQUATION CALCULATIONS
Once an equation is balanced, it can be used to calculate how many grams or moles of one
material involved in the equation will react with another material or how many grams or
moles of one material will be formed from another material. These calculations are called
stoichiometric calculations.
stoichiometric calculations
1. Obtain a balanced equation.
2. Set up the form around the balanced equation:
a. Molecular weights above each formula
b. Moles and grams written successively below each formula
3. Put the information given in the problem in its correct place (under substance it belongs
with; this is what we call the known substance since we have information given about it).
4. Do the calculations using the following equations.
1. How many grams of NaCl would be formed from 100 grams of Na2CO3 in the following
reaction? Na2CO3 + 2 HCl → 2 NaCl + CO2 + H2O
Na2CO3 + 2 HCl → 2 NaCl + CO2 + H2O
(100 grams Na2CO3 / 105.99) = 0.9435 moles Na2CO3
0.9435 moles Na2CO3 x (2 / 1) = 1.887 moles NaCl
1.887 moles NaCl x 58.44 = 110.3 grams of NaCl
2. How many moles of Fe would be formed from 50 grams of Fe3O4 in the following
equation?
Fe3O4 + 4 H2 → 3 Fe + 4 H2O
Fe3O4 + 4 H2 → 3 Fe + 4 H2O
(50 grams Fe3O4 / 231.55) = 0.2159 moles Fe3O4
0.2159 moles Fe3O4 x (3 / 1) = 0.648 mol of Fe
3. How many grams of SO2 would be formed from 60 grams of FeS2 in the following
reaction?
4 FeS2 + 11 O2 → 2 Fe2O3 + 8 SO2
4 FeS2 + 11 O2 → 2 Fe2O3 + 8 SO2
(60 grams FeS2 / 119.99) = 0.5000 moles FeS2
0.5000 moles FeS2 x (8 / 4) = 1.00 mole SO2
1.00 mole SO2 x (64.07) = 64.1 grams of SO2
4. How many moles of NH4NO2 would be required to form 25 grams of N2 in the following
reaction?
NH4NO2 → N2 + 2 H2O
NH4NO2 → N2 + 2 H2O
(25 grams N2 / 28.02) = 0.8922 moles N2
0.8922 moles N2 x (1 / 1) = 0.892 mol of NH4NO2
2.10: SOLUTION CONCENTRATION
Solutions are one of the types of mixtures known as a homogenous mixture, in which two or
more materials are combined to form a single phase that has the same composition,
properties, and appearance throughout. Salt or sugar dissolved in water is an example of a
solution. The minor component of the mixture is the material being dissolved, also called
the solute (salt or sugar in the examples given). The major component is the material doing
the dissolving, also called the solvent (water in the examples given). Solutes can be of two
types: (1) electrolytes, which are ionic, or (2) very polar compounds, which form ions when
they dissolve. Solutions of electrolytes (like salt) conduct an electric current. Solutions of
solutes that form molecules when they dissolve (like sugar) do not conduct an electric
current and are called nonelectrolytes.
concentration
The amount of solute present in a certain amount of solvent is referred to as the
concentration of the resulting solution. Solutions are often described as concentrated or
dilute, which refers to the relative amount of solute present. "Concentrated" means there is
a relatively large amount of solute, and "dilute" means there is a relatively small amount of
solute. There are three common concentration terms used in chemistry: mass percent,
molarity, and molality.
Mass Percent
The concentration term mass percent refers to the mass of solute present per 100 grams of
solution (solute + solvent) and can be determined by the following formula:
A solution prepared by dissolving 10.5 grams of C2H5OH in 230 grams of water would have
what mass percent?
Mass percent = 10.5 g / (10.5 g + 230 g) x 100% = 4.37% (by mass)
Molarity (M)
The concentration term molarity (M) refers to the moles of solute present per liter of
solution and can be determined by the following formula:
Note here that the solute quantity is expressed in moles (grams / molecular weight) and
volume is of the total solution (not solvent added), since volume is usually measured in ml
(liters = ml / 1000). The symbol M is used for molarity.
A solution prepared by dissolving 10.5 grams of C2H5OH in enough water to make 230 ml
of solution would have what molarity?
Molarity = (10.5 g / 46.068) / (230 ml / 1000 ml/L) = 0.991 M C2H5OH
Molality (m)
The concentration term molality (m) refers to the moles of solute present per kilogram of
solvent and can be determined by the following formula:
Note here that the solute quantity is expressed in moles (grams / molecular weight) and
quantity of solvent expressed in kilograms, since this is usually measured in grams (kg =
grams / 1000). The symbol m is used for molality.
A solution prepared by dissolving 10.5 grams of C2H5OH in 300 grams of water would have
what molarity?
molality = (10.5 g / 46.068) / (300 g / 1000 g/kg) = 0.760 m C2H5OH
Show the calculation of the volume of 0.987 M solution which can be prepared using 24.6
grams of NaNO3.
mlsolution = (gsolute x 1000) / (MW x M) = (24.6 x 1000) / (85.0 x 0.987) = 293 ml
10. Show the calculation of the volume of 0.238 M solution which can be prepared using
13.4 grams of Ca3(PO4)2.
mlsolution = (gsolute x 1000) / (MW x M) = (13.4 x 1000) / (310.18 x 0.238) = 182 ml
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