chapter 4 4.3 chemical reactions in the lab physical and chemical change
TRANSCRIPT
CHAPTER 4
4.3 Chemical Reactions in the Lab
Physical and Chemical
Change
2 4.3 Chemical Reactions in the Lab
Why would the presence of water on Mars be a sign that life might exist there?
3 4.3 Chemical Reactions in the Lab
Many reactions, including those that sustain life, involve chemicals dissolved in water.
Why would the presence of water on Mars be a sign that life might exist there?
4 4.3 Chemical Reactions in the Lab
DRY
Light blue powder
No reaction
5 4.3 Chemical Reactions in the Lab
DRY
No reaction
IN SOLUTION
Light blue powder NaS(aq) CuSO4(aq)
Chemical reaction
A precipitate is an insoluble compound.
6 4.3 Chemical Reactions in the Lab
A solution with water as the solvent is called an aqueous solution.
“Aqua” means “water.”
SYMBOLS
(s) indicates a solid
(l) indicates a liquid
(g) indicates a gas
(aq) indicates a substance dissolved in water (an aqueous solution)
7 4.3 Chemical Reactions in the Lab
S O
O
O
OCu
Cu
S O
O
O
O
2–
2+
OH
H
OH
H
OH
HO
H H
A salt is an ionic compound that forms ions when dissolved in water.
8 4.3 Chemical Reactions in the Lab
Can you translate what you see into a chemical equation?
9 4.3 Chemical Reactions in the Lab
Can you translate what you see into a chemical equation?
Zn(s) + CuSO4(aq)Cu(s)
and Zn(s) is disappearing
10 4.3 Chemical Reactions in the Lab
Zn(s) + CuSO4(aq)Cu(s)
and Zn(s) is disappearing
Can you translate what you see into a chemical equation?
a salt in water!
11 4.3 Chemical Reactions in the Lab
Cu2+(aq)
SO42–(aq)
Can you translate what you see into a chemical equation?
Zn(s) +Cu(s)
and Zn(s) is disappearing
12 4.3 Chemical Reactions in the Lab
Cu2+(aq)
SO42-(aq)
Zn(s) +Cu(s)
and Zn(s) is disappearing
The copper ion gains 2 electrons to form solid copper.
reduction: a chemical reaction that decreases the charge of an atom or ion by accepting electrons.
Cu2+(aq) + 2e– Cu(s)
13 4.3 Chemical Reactions in the Lab
Cu2+(aq)
SO42-(aq)
Zn(s) +Cu(s)
and Zn(s) is disappearing
The copper ion gains 2 electrons to form solid copper.
Where could those electrons
come from?
Cu2+(aq) + 2e– Cu(s)
14 4.3 Chemical Reactions in the Lab
Cu2+(aq)
SO42-(aq)
Zn(s) +Cu(s)
and Zn(s) is disappearing
Zn(s) Zn2+(aq) + 2e–
Zinc gives up 2 electrons to become a zinc ion, dissolved in water.
Cu2+(aq) + 2e– Cu(s)
15 4.3 Chemical Reactions in the Lab
Zn(s) Zn2+(aq) + 2e–
Zinc gives up 2 electrons to become a zinc ion, dissolved in water.
oxidation: a chemical reaction that increases the charge of an atom or ion by giving up electrons.
16 4.3 Chemical Reactions in the Lab
Cu2+(aq) + 2e– Cu(s)
Reactants Products
reduction
REACTION NAME
17 4.3 Chemical Reactions in the Lab
Cu2+(aq) + 2e– Cu(s)
Zn(s) Zn2+(aq) + 2e–
Reactants Products
reduction
REACTION NAME
oxidation
18 4.3 Chemical Reactions in the Lab
Cu2+(aq) + 2e– Cu(s)
Zn(s) Zn2+(aq) + 2e–
Reactants Products
reduction
REACTION NAME
oxidation
These 2 reactions are happening at the same time.
To obtain the overall reactionadd the reactants, then the products.
19 4.3 Chemical Reactions in the Lab
Cu2+(aq) + 2e– Cu(s)
Zn(s) Zn2+(aq) + 2e–
Reactants Products
Cu2+(aq) + Zn(s) Cu(s) + Zn2+(aq)
reduction
REACTION NAME
oxidation
redox
20 4.3 Chemical Reactions in the Lab
O
H HO
H
H- +
dissociation
H2O OH– + H+
The double arrow indicates that the reaction goes in both ways.
The heavier arrow means that the reverse reaction is favored.
21 4.3 Chemical Reactions in the Lab
Classify these items as acids or bases.
22 4.3 Chemical Reactions in the Lab
HCl(l) H+(aq) + Cl–(aq)H2O(l)
acid: a chemical that dissolves in water to create more H+ ions than there are in neutral water.
Acids give foods like lemons their sour taste.Acids react with metal to create hydrogen gas (H2).Acids can corrode metal and burn skin.
Example:
Hydrochloric acid
23 4.3 Chemical Reactions in the Lab
NaOH(l) Na+(aq) + OH–(aq)H2O(l)
Bases create a bitter taste.Bases have a slippery feel, like soap.Bases can neutralize acids.
Example:
Sodium hydroxide
24 4.3 Chemical Reactions in the Lab
NaOH(l) Na+(aq) + OH–(aq)H2O(l)
Bases create a bitter taste.Bases have a slippery feel, like soap.Bases can neutralize acids.
Example:
Sodium hydroxide
OH–(aq) + H+(aq) H2O(l)
Result: fewer H+ ions
25 4.3 Chemical Reactions in the Lab
NaOH(l) Na+(aq) + OH–(aq)H2O(l)
Example:
Sodium hydroxide
OH–(aq) + H+(aq) H2O(l)
Result: fewer H+ ions
base: a chemical that dissolves in water to create fewer H+ ions (or more OH– ions)than there are in neutral water.
26 4.3 Chemical Reactions in the Lab
27 4.3 Chemical Reactions in the Lab
Higher H+ concentration Lower H+ concentration
The pH scale helps to determine whether a solution is acidic or basic.
28 4.3 Chemical Reactions in the Lab
A solution with water as the solvent is called an aqueous solution.
Redox reactions
(transfer of electrons)
Acid-base reactions
(transfer of protons, H+ ions)
two types of chemical reactions that take place in an aqueous environment.
Higher H+ concentration Lower H+ concentration