Download Experiment 11: Acidity and Basicity

Experiment 10: Determining Chemical Reactivity
 A chemical reaction is said to occur when changes are observed.
Examples of Chemical Reaction
1. Release of gas
2. Formation of precipitate
3. Change in color
4. Change in mass
5. Change in temperature
 Elements are more reactive if it is further left of the periodic table or further down.
 Metal atoms have only a few electrons in their outermost electron shell.
 Reactivity of metals increases as you go down the group because the outer electrons are
further from the nucleus.
Activity Series of Metals
Rb, K, Na, Ca, Mg, Al, Zn, C, Cr, Fe, Ni, Sn, Pb, H, Cu, Bi, Sb, Hg, Ag, Pt, Au
 Metals above hydrogen react with acid to produce hydrogen gas.
o Examples:
Zn + H2SO4 → ZnSO4 + H2
2Na + 2HCl → 2NaCl + H2
Ca + H2O → Ca(OH)2 + H2
Observations
A. CuSO4
NH4OH
CuSO4 + NH4OH
Light blue solution
Colorless
Dark blue solution
CuSO4
+
NH4OH
→
(NH4)2SO4 +
Dissolves
B. HCl + Fe
HCl + Cu
HCl + Mg
HCl + Al
Cu(OH)2
dark blue
Observations
Release of gas, formation of rust
NO REACTION
Release of heat, release of gas, disappearance of the substance
Release of heat, release of gas
HCl
HCl
HCl
HCl
+
+
+
+
Fe2+
Cu
Mg
Al
→ FeCl2 (rust)
→
→ MgCl2
→ AlCl3
Observations
C. ZnSO4
BaCl2
ZnSO4 + BaCl2
Colorless
Colorless
Clear solution with white precipitate
ZnSO4
+
BaCl2
→
BaSO4
White precipitate
+ ZnCl
Experiment 11: Types of Chemical Reactions
 Types of Chemical Reaction
1. Combination – a reaction in which two or more substances combine to form a
single product.
A + B → AB
2. Decomposition – a reaction in which a single substance breakdown into two or
more substances.
AB → A + B
3. Single Replacement - a reaction in which one element reacts by taking the
place of another element in a compound.
A + BC → AC + B
4. Double Replacement – the reaction in which the positive ion from one
compound takes the negative ion of another compound and the remaining
ions also combine to from another ionic compound.
AB + CD → AD + CB
 A chemical equation is not considered valid until it is balanced.
Observations
A. 1. Fe nail in a bottle
Fe nail + moist
2. H2O
+ NaOH + phenolphthalein
+ breath
Fe3+
+ O2
→
No reaction
Formation of rust
Colorless
Dark pink solution
Colorless
Fe2O3
Iron oxide or rust
2NaOH + 2CO2 →
2NaCO3 + H2
Observations
B.1. (NH4)2CO3
+ moist RLP
+ moist BLP
2. CoCl2.6H2O
+ Heat
3. BaCl2.2H2O
+ Heat
Pungent odor
Changed to blue litmus paper
No change
Red-violet crystals
Blue powder + moisture droplets
White powder
It became lighter
(NH4)2CO3 → NH3 + H2O + CO2
CoCl2.6H2O + heat → CoCl2 + 6H2O
BaCl2.2H2O + heat → BaCl2 + 2H2O
Observations
C.1. CuSO4 + Fe
2. KI + Cl2
+ starch
CuSO4 + Fe →
Formation of rust
Yellow solution
Dark solution
FeSO4 + Cu
rust
2KI + Cl2 →
2KCl + I2
yellow
Observations
Cloudy solution with white precipitate
Dark red/maroon solution
D.1. NaCl + AgNO3
2. KSCN + FeCl3
NaCl + AgNO3 → AgCl + NaNO3
precipitate
3KSCN + FeCl3 →
3KCl + Fe(SCN)3
Deep red
 The carbon dioxide in our breath reacts with the NaOH solution, which results to a change
in its color.
 Iron is more reactive than copper.
 The presence of iodine was confirmed by the addition of starch.
Experiment 12 – Oxidation – Reduction Reactions
 Oxidation-Reduction or redox – reactions in which transfer of electrons take place.
 Oxidation Number
o For ionic compounds, the oxidation number is equal to the number of
electrons lost or gained.
 It is the same as the charge on the ion.
Examples: NaCl = Na+1; Cl-1
MgBr2 = Mg+2; Br-1
o For covalent compounds:
1. All elements in their free state have an oxidation number of zero.
2. The oxidation number of oxygen is -2 (except in peroxides, -1).
3. Oxidation number of hydrogen is +1 (except in metal hybrides, -1).
4. The sum of oxidation numbers must be equal to zero (all coumpounds
are electrically neutral).
5. All elements in Group IA have an oxidation number of +1.
6. All elements in Group IIA have an oxidation number of +2.
Oxidation Number of Some Elements
Hydrogen
+1
Chloride
Sodium
+1
Bromide
Potassium
+1
Iodide
Silver
+1
Sulfide
Ammonium
+1
Oxide
Calcium
+2
Magnesium
+2
Aluminum
+3
Iron
+2; +3
Copper
+1; +2
Tin
+2; +4
-1
-1
-1
-2
-2
 Oxidation – loss of electrons which cause an atom or an ion to have either a decrease in
negative charge or an increase in positive charge.
 Involves the gain of oxygen and loss of hydrogen
 Reduction – gain of electrons which cause the atom or ion to have an increase in negative
charge or decrease in positive charge.
 Involves the loss of oxygen and gain of hydrogen
 Reducing agent – the substance in the reaction which gives up electrons.
–It is the substance that is oxidized.
 Oxidizing agent – The substance which takes up (or receives) these electrons.
–It is the substance that is reduced.