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Unformatted text preview: Chapter 4
Chemical Quantities and Aqueous Reactions Quantities in Chemical Reactions 1. Write balanced chemical equation
2. Convert quantities of known substances into moles
4. Convert moles of sought quantity into desired units Reaction Stoichiometry
• The coefficients in a balanced chemical
equation specify the relative amounts in moles
of each of the substances involved in the
2 C8H18(l) + 25 O2(g) ! 16 CO2(g) + 18 H2O(g) 2 moles of C8H18 react with 25 moles of O2
to form 16 moles of CO2 and 18 moles of H2O Predicting Amounts from Stoichiometry
• The amounts of any other substance in a
• chemical reaction can be determined from the
amount of just one substance
How much CO2 can be made from 22.0 moles of
C8H18 in the combustion of C8H18?
2 C8H18(l) + 25 O2(g) ! 16 CO2(g) + 18 H2O(g) Practice - How many moles of water are made in the
combustion of 0.10 moles of glucose?
C6H12O6 + 6 O2 ! 6 CO2 + 6 H2O
Relationships: Solution: Check: Mass (g) of
Compound A Mass (g) of
Compound B Use molar mass
of Compound A Moles of
Compound A Use mole ratios
of A and B
equation Use molar mass
of Compound B Moles of
Compound B Example 4.1: How many grams of glucose can be
synthesized from 37.8 g of CO2 in photosynthesis?
Relationships: Solution: Check: The Limiting Reactant (6)
(12) Limiting Reagent Limiting and Excess Reactants in the
Combustion of Methane
CH4(g) + 2 O2(g) ! CO2(g) + 2 H2O(g) • If we have 5 mols of CH4 and 8 mols of O2, which is
the limiting reactant? Practice — How many moles of Si3N4 can be made from
1.20 moles of Si and 1.00 moles of N2 in the reaction
3 Si + 2 N2 ! Si3N4?
Relationships: Solution: Reaction Yield
Theoretical Yield Actual Yield is the amount of product actually obtained
from a reaction. Let’s do one together….
Titanium is a strong, lightweight, corrosion-resistant metal that is used
in rockets, aircrafts, jet engines, and bicycle frames. It is prepared by
the reaction of titanium (IV) chloride with molten magnesium at high
TiCl4 + 2Mg ! Ti + 2MgCl2
In a certain industrial operation, 3.54 x 107 g of TiCl4 are reacted with
1.13 x 107 g of Mg. Calculate the percent yield of Ti if 7.91 x 106 g of
Ti are produced. Solutions
A solution is a homogenous mixture of 2 or more substances regardless of state The solute is(are) the substance(s) present in the
what is dissolved
The solvent is the substance present in the larger
does the dissolving
Solution Solvent Solute Solution Concentration
• Qualitatively, solutions are
• often described as dilute or
Dilute solutions have a
small amount of solute
compared to solvent
have a large amount of
solute compared to solvent Concentration = amount of solute in a given amount of solution Solution Concentration: Molarity
molarity, M = amount of solute (in moles) / amount of solution (in L) What mass of KI is required to make 500 mL of
a 2.80 M KI solution?
volume KI moles KI grams KI ***always start with the given information that has 1 unit 500 ml x (1L/1000mL) x (2.8 mol KI/1 L soln) x (166g KI/1mol KI) = 232g KI Example 4.5: Find the molarity of a solution that has
25.5 g KBr dissolved in 1.75 L of solution
Plan: 25.5g KBr, 1/75 L solution
g KBr x (mol KBr/L sol'n) = M Relationships: Solution: 25.5 g KBr x (1mol KBr/119.00g KBr) = .21429 mol KBr
(.21429 mol/ 1.75 L) = .12245 L solution Check: Example 4.6: How many liters of 0.125 M
NaOH contain 0.255 mol NaOH?
Plan: moles to L Relationships: Solution: Check: 0.255 mol NaOH x (1L solution/0.125 mol NaOH) = 2.04 L solution Dilution
Dilution is the procedure for preparing a less concentrated solution from a more concentrated
Add Solvent Moles of solute
before dilution (1) = M1 x V1 = M2 x V2 Moles of solute
after dilution (2) Example 4.7: To what volume should you dilute
0.200 L of 15.0 M NaOH to make 3.00 M NaOH?
Relationships: Solution: Check: [(15.0 mol/L) x (.200L)] / (3.00 mol/L) = 1.00L Practice – What is the concentration of a solution prepared
by diluting 45.0 mL of 8.25 M HNO3 to 135.0 mL?
Relationships: Solution: Check: [(8.25 mol/L) x (45.0mL)] / (135.0 mL) = 2.75mol/L = 2.75M Practice – How would you prepare 200.0 mL of 0.25 M NaCl solution from a 2.0 M solution?
Relationships: Solution: [(.25 mol/L) x (200.0mL)] / (2.00 mol/L) = 25mL
so you've added 175mL of water Check: Solution Stoichiometry
• Because molarity relates the moles of solute to
the liters of solution, it can be used to convert
between amount of reactants and/or products
in a chemical reaction Example 4.8: What volume of 0.150 M KCl is required to
completely react with 0.150 L of 0.175 M Pb(NO3)2 in the
reaction 2 KCl(aq) + Pb(NO3)2(aq) ! PbCl2(s) + 2 KNO3(aq)?
Solution: Check: .150 L Pb (NO3)2 x (1.75 mol/ 1 L) x (2 mol/ 1 mol) x ( 1 L/ .150 mol) = .350 L KCl What Happens When a Solute Dissolves?
• There are attractive forces between the solute
particles holding them together • there are also attractive forces between the colvent molecules • When we mix the solute with the solvent, there are attractive forces between the solute particles and the
solvent molecules • if the attractions between solute and solvent are strong enough, the solute will dissolve for dissolution to occure solute-solvent interactions must
be stronger than solute-solute and solvent-solute
interactions (might be written wrong) Electrolytes and Nonelectrolytes
• Materials that dissolve • in water to form a
solution that will
conduct electricity are
Materials that dissolve
in water to form a
solution that will not
conduct electricity are
called nonelectrolytes Salt vs. Sugar Dissolved in Water ionic compounds dissociate into ions
when they dissolve
ELECTROLYTE molecular compounds do not dissociate
when they dissolve
NON-ELECTROLYTE Conduct electricity in solution?
Cations (+) and Anions (-) Strong Electrolyte – 100% dissociation
NaCl (s) H 2O Na+ (aq) + Cl- (aq) Weak Electrolyte – not completely dissociated
CH3COOH CH3COO- (aq) + H+ (aq) A reversible reaction. The reaction can occur in both directions Hydration +
O : slightly negative H 2O "+#
- H : slightly positive *****************************
************ Solubility Rules *************************
know this chart Practice – Determine if each of the
following is soluble in water
PbSO4 anything with K is soluble no yes yes, becasue of Nitrate no, it is an exception 2 KI(aq) + Pb(NO3)2(aq) ! PbI2(s) + 2 KNO3(aq) • Precipitation
are reactions in which a solid
forms when we mix two
solutions No Precipitate Formation =
KI(aq) + NaCl(aq) ! KCl(aq) + NaI(aq)
all ions still present, $ no reaction no reaction Ionic Equations
• Equations that describe the chemicals put into the
water and the product molecules are called molecular
equations • Equations that describe the material’s structure when
dissolved are called complete ionic equations
" aqueous strong electrolytes are written as ions
# soluble salts, strong acids, strong bases " insoluble substances, weak electrolytes, and nonelectrolytes
are written in molecule form
# solids, liquids, and gases are not dissolved, therefore molecule form Ionic Equations
• Ions that are both reactants and products are called
spectator ions $ An ionic equation in which the spectator ions are
removed is called a net ionic equation Example 4.10: Write the equation for the
precipitation reaction between an aqueous
solution of potassium carbonate and an aqueous
solution of nickel(II) chloride
1. Write the formulas of the reactants
2. Determine the possible products
a) determine the ions present
b) exchange the Ions
c) write the formulas of the products
# balance charges Acids
Have a sour taste. Vinegar owes its taste to acetic acid. Citrus
fruits contain citric acid.
Cause color changes in plant dyes.
React with certain metals to produce hydrogen gas.
2HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g) React with carbonates and bicarbonates to produce carbon
2HCl (aq) + CaCO3 (s) CaCl2 (aq) + CO2 (g) + H2O (l) Aqueous acid solutions conduct electricity. Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.
Cause color changes in plant dyes opposite that of acids.
Aqueous base solutions conduct electricity. 4.3 Arrhenius acid Arrhenius base NaOH is a substance that produces H+(H3O+) in water is a substance that produces OH- in water Na+ +
OH- Hydronium ion, hydrated proton, H3O+ Electron rich region electron poor region A Brønsted acid
A Brønsted base base acid is a ptoton donor is a proton acid base A Brønsted acid must contain at least one
ionizable proton! Strong Acids
Perchloric acid HCl
HClO4 completly dissociate Weak Acids
Acetic acid Bases HF
CH3COOH reversible reactoins Monoprotic acids
HCl H+ + Cl- HNO3 H+ + NO3- CH3COOH H+ + CH3COO- Diprotic acids
H2SO4 H+ + HSO4- HSO4- H+ + SO42- Triprotic acids
H2PO4HPO42- H+ + H2PO4H+ + HPO42H+ + PO43- strong electrolyte Identify each of the following species as a Brønsted acid,
base. (a) HI, (b) CH3COO-.
HI (aq) H+ (aq) + Br- (aq) CH3COO- (aq) + H+ (aq) Bronsted CH3COOH (aq)
bronsted base 4.3 Neutralization Reaction
acid + base
HCl (aq) + NaOH (aq)
H+ + Cl- + Na+ + OHH+ + OH- salt + water
NaCl (aq) + H2O
Na+ + Cl- + H2O
H 2O H2SO4 (aq) + 2NaOH (aq) Na2SO4 (aq) + 2H2O 2H+ + SO42- + 2Na+ + 2OH- 2Na+ + SO42- + 2H2O H+ + OH- H 2O 4.3 Practice – Predict the products and
balance the equation
HCl(aq) + Ba(OH)2(aq) ! H2SO4(aq) + Sr(OH)2(aq) !# Acid-Base Titrations
In a titration a solution of accurately known concentration is
added gradually added to another solution of unknown
concentration until the chemical reaction between the two
solutions is complete.
Equivalence point – the point at which the reastoin is complete Indicator – Slowly add base
to unknown acid
changes color Titration What volume of a 1.420 M NaOH solution is
Required to titrate 25.00 mL of a 4.50 M H2SO4
solution? WRITE THE CHEMICAL EQUATION!
H2SO4 + 2NaOH 2H2O + Na2SO4 Let’s do one more… What volume of a 1.420 M NaOH solution is
required to titrate 25.00 mL of a 1.500 M
H3PO4 solution? Practice — What is the concentration of NaOH solution that
requires 27.5 mL to titrate 50.0 mL of 0.1015 M H2SO4?
2 NaOH(aq) + H2SO4(aq) ! Na2SO4(aq) + 2 H2O(aq)
Solution: Check: Other Patterns in Reactions
• The precipitation and acid-basereactions all
involve exchanging the ions in the solution • redox reactions
" also known as
" many involve the reaction of a substance with O2(g) 4 Fe(s) + 3 O2(g) ! 2 Fe2O3(s) Redox Reactions
(electron transfer reactions)
2Mg (s) + O2 (g) 2Mg
O2 + 4e- 2Mg2+ + 4e2O2- 2MgO (s) oxidation half reaction (lose e-) reductino half-reaction (gain e-) 2Mg + O2 + 4e2Mg + O2 2Mg2+ + 2O2- + 4e2MgO Zn0 C u0 CuSO4 AgNO3 Metal Displacement Reaction
Zn (s) + CuSO4 (aq)
Zn ZnSO4 (aq) + Cu (s) Zn2+ + 2e- Zn is oxidized Cu2+ + 2e- Cu Cu2+ is reduced Z n is the reducing agent Cu2+ is the oxidizing agent LEO the lion goes GER!
(lose electron oxidized)
(Gain Elections Reduced) Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction? Oxidation number
The charge the atom would have in a molecule (or an
ionic compound) if electrons were completely transferred.
1. Free elements (uncombined state) have an oxidation
number of zero.
Na, Be, K, Pb, H2, O2, P4 = 0 2. In monatomic ions, the oxidation number is equal to
the charge on the ion.
Li+, Li = +1; Fe 3+, Fe = +3 3. The oxidation number of oxygen is usually –2. In H2O2
and O22- it is –1. 4. The oxidation number of hydrogen is +1 except when
it is bonded to metals in binary compounds. In these
cases, its oxidation number is –1 (LiAlH4). 6. The sum of the oxidation numbers of all the atoms in a
molecule or ion is equal to the charge on the molecule
or ion. Figure 4.10 The oxidation numbers of elements in their compounds Practice – Assign an oxidation state
to each element in the following
• Br2 Br = 0 • K+ K= +1 • LiF Li= +1 & F= -1 • CO2 0=-2, C= +4 • SO42! 0=-2, S= +6 • Na2O2 Oxidation and Reduction
• Oxidation occurs when an atom’s oxidation
• state increases during a reaction
Reduction occurs when an atom’s oxidation
state decreases during a reaction Practice – Assign oxidation states,
determine the element oxidized and reduced,
and determine the oxidizing agent and
reducing agent in the following reactions: ...
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