chapter 4 4.3 chemical reactions in the lab physical and chemical change

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