Recap – Formula and bonding
Types of bonding: ionic, covalent, metallic
Types of formula: empirical, molecular, structural
HO
H2O2
Type of covalent materials: molecular, network
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Polarity of Water
Fig. 4.2 Silberberg
• The O-H bonds in water are polar.
• The angular shape of the molecule
mean water is a ‘polar molecule’.
2
Chemical Reactions
Chemical reactions occur because:
• Products contain less energy than reactants and
systems go to lowest energy state, eg burning gas.
• Energy supplied to force reactants to products which
have higher energy, eg blast furnace.
3
Chemical Equations
• Word Equation
hydrogen plus oxygen forms water
• Symbolic Equations – use correct formula
H2 + O2  H2O
• Need to balance equations. Indicate states
2H2(g) + O2(g)  2H2O(l)
4
Chemical Equations
• Molecular Equation
eg
H2(g) + I2(g)  2HI(g)
C6H12O6(s)
 C6H12O6(aq)
• Ionic Equations
eg
NaCl (s)  Na+(aq) + Cl-(aq)
Pb2+(aq) + 2I-(aq)  PbI2(s)
Precipitate
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Reactions with Acid, H+
• H+ cation is just a ‘bare proton’, no e-.
- e-
Hydrogen
atom
H+
Hydrogen
ion
• In aqueous solution, H+ associates with H2O to give
H3O+(aq), also called H+(aq).
+
H
O
H
H
• Substances that provide H+ ions in water are
called ACIDS.
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Metal + Acid  Salt + Hydrogen
Formula Equation
Zn + 2HCl  ZnCl2 + H2
Complete ionic equation
Zn(s) + 2H+(aq) + 2Cl-(aq)  Zn2+(aq) + H2(g) + 2Cl-(aq)
Net ionic equation
Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g)
We can isolate the salt by evaporation of the solvent
Zn2+(aq) + 2Cl-(aq)  ZnCl2(s)
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Carbonate + Acid  Salt + H2O + CO2
Formula Equation
CaCO3 + 2HCl  CaCl2 + H2O + CO2
Complete ionic equation
CaCO3(s) +2H+(aq) + 2Cl-(aq)  Ca2+(aq) + H2O(l) +
CO2(g) + 2Cl-(aq)
Net ionic equation
CaCO3(s) + 2H+(aq)  Ca2+(aq) + H2O(l) + CO2(g)
We can isolate the salt by evaporation of the solvent
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Ca2+(aq) + 2Cl-(aq)  CaCl2(s)
Learning Outcomes:
• By the end of this lecture, you should:
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understand the reason that water dissolves some ionic
materials
know the component parts of a chemical equation
be able to balance a chemical equation
recognise a molecular equation, formula equation and an
ionic equation
be able to describe a chemical reaction in terms of a
chemical equation
understand an acid supplies H+ ions and exists in water
recognise reactions involving dissolution, precipitation and
acids
be able to complete the worksheet (if you haven’t already
done so…)
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Questions to complete for next lecture:
1. Balance the following chemical equations:
a)
CH4(g) + O2(g)  CO2(g) + H2O(l)
b)
CaCl2
c)
Ag+(aq) + CrO42-(aq)  Ag2CrO4(s)
d)
Ca(s) + H+(aq)  Ca2+(aq) + H2(g)
e)
Mg(OH)2(s) + H+(aq)  Mg2+(aq) + H2O(l)
+ AgNO3  Ca(NO3)2 + AgCl
2. Classify the above equations as ‘molecular’, ‘formula’, or ‘net ionic’.
3. Which of the equations in question 1 represent a precipitation
reaction?
4. Which of the equations in question 1 represent a reaction with acid?
5. Would it matter if you used hydrochloric acid or sulfuric acid to
perform the reaction represented by equation 1d?
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