Transcript TYPES OF REACTIONS

TUTS
• Check chem foyer for new tut group lists after
1pm on Monday 22 August.
TEST 1
• Wed 24 August during the tut
• Quantitative chemistry, types of reactions
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TYPES OF REACTIONS
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Electrolytes
Acid- base reactions
Solubility rules
Precipitation reactions
Writing ionic equations
Oxidation numbers
Redox reactions
Concentration
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ELECTROLYTES
“ionic compounds which dissociate in water to produce ion
counterparts”
- ions conduct electricity
- Strong electrolytes: ionic compounds which
completely dissociate in water (includes strong
acids & bases* and soluble* ionic salts)
- Weak electrolytes: ionic compounds which
partially dissociate in water
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ACID-BASE REACTIONS
ACID + BASE → SALT + H2O
One H+ from the acid and one OH- from the base form H2O
e.g. HCl + NaOH → NaCl + H2O
STRONG ACIDS
STRONG BASES
HCl
LiOH
HBr
NaOH
HI
KOH
HClO3
RbOH
HClO4
CsOH
HNO3
Ca(OH)2
H2SO4
Sr(OH)2
Ba(OH)2
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SOLUBILITY RULES
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Salts of Group I and ammonium ions are soluble.
Nitrates, acetates, and perchlorates are soluble.
Salts of Ag, Hg(I), and Pb are insoluble.
Chlorides, bromides and iodides are soluble.
Carbonates, hydroxides, sulphides, oxides, silicates,
and phosphates are insoluble. (Sulphides of Group II
ions and hydroxides of Ca2+, Sr2+ and Ba2+ are slightly
soluble).
6. Sulfates are soluble, except those of barium,
strontium.
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PRECIPITATION REACTIONS
• Use solubility rules to predict insoluble
products
• Generally reaction is:
AB + CD →AD + CB
Try:
Pb(NO3)2 (aq) + 2KI (aq) → PbI2 ? + 2KNO3 ?
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WRITING IONIC EQUATIONS
• Balanced molecular equation
• Balanced overall ionic equation (note ppts)
• Remove spectator ions to give net ionic
equation
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PRACTICE EXAMPLE
BaCl2 + H2SO4 → BaSO4 + HCl
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PRACTICE EXAMPLE
H2SO4(aq) + NaOH(aq) →
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OXIDATION NUMBERS
1. Elements in their elemental form have an oxidation number of 0.
2. The oxidation number of a monatomic ion is the same as its charge.
3. Nonmetals tend to have negative oxidation numbers, although some
are positive in certain compounds or ions.
– Oxygen has an oxidation number of −2, except in the peroxide ion in
which it has an oxidation number of −1.
– Hydrogen is −1 when bonded to a metal, +1 when bonded to a
nonmetal.
– Fluorine always has an oxidation number of −1.
– The other halogens have an oxidation number of −1 when they are
negative; they can have positive oxidation numbers, however, most
notably in oxyanions.
4. The sum of the oxidation numbers in a neutral compound is 0.
5. The sum of the oxidation numbers in a polyatomic ion is the charge
on the ion.
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PRACTICE EXAMPLES
S2O32FeO42-
Na2SO3
S8
NH4+
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REDOX REACTIONS
OIL RIG
• Atoms/ions are reduced by oxidising agents or
oxidised by reducing agents
• Balance redox reactions in either acidic or
basic medium
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Acidic medium
1. Write reduction and oxidation half -equations
2. Balance half-equations
 Atoms other than H and O
 O atoms (add H2O)
 H atoms (adding H+)
3. Balance charge with electrons
4. Combine half-reactions
5. Simplify
6. Verify
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PRACTICE EXAMPLE
Fe2+(aq) + MnO4¯  Fe3+(aq) + Mn2+(aq)
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Basic medium
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Write reduction and oxidation half -equations
Balance half-equations
 Atoms other than H and O
 O atoms (add H2O)
 H atoms (adding H+)
Balance charge with electrons
Combine half-reactions
Add number of OH- ion equal to number of H+ ions on both sides of
overall reaction and combine hydrogen ions and hydroxide ions to
form water when they appear on the same side of the equation.
Simplify
Verify
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PRACTICE EXAMPLE
S(s) + ClO¯(aq)  SO32- (aq) + Cl¯(aq)
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CONCENTRATION
The concentration of a solution is the amount of solute present in a given quantity of
solvent or solution.
- can be expressed in various ways e.g. parts per million, mass
percent and most commonly molarity.
Molarity (M) (molar concentration)
- the number of moles of solute in 1 litre of solution.
Molarity = moles of solute (n)
volume of solution in litres (V)
REMEMBER STOICHIOMETRIC RATIOS
n
M
V
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PRACTICE EXAMPLE
Calculate the molarity of a solution made by dissolving 5.00 g of glucose,
C6H12O6 , in sufficient water to form exactly 100 mL of solution.
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PRACTICE EXAMPLE
How many grams of NaOH are needed to neutralise 20.0 cm3 of 0.150 M H2SO4
solution?
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Dilution of solutions
Dilution is a procedure for preparing a less concentrated
solution from a more concentrated one.
moles of solute before dilution = moles of solute after dilution
Mconc × Vconc = Mdil × Vdil
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