Chemical Reactions

Chapter 13

Acids

• Have a sour taste. Vinegar owes its taste to acetic acid.Have a sour taste. Vinegar owes its taste to acetic acid.Citrus fruits contain citric acid.Citrus fruits contain citric acid.

• React with certain metals to produce hydrogen gas.React with certain metals to produce hydrogen gas.

• React with carbonates and bicarbonates to produce carbon React with carbonates and bicarbonates to produce carbon dioxide gas.dioxide gas.

• Cause color changes in plant dyes.Cause color changes in plant dyes.

2HCl (2HCl (aqaq) + Mg () + Mg (ss) MgCl) MgCl22 ( (aqaq) + H) + H22 ( (gg))

2HCl (2HCl (aqaq) + CaCO) + CaCO33 ( (ss) CaCl) CaCl22 ( (aqaq) + CO) + CO22 ( (gg) + H) + H22O (O (ll))

• Aqueous acid solutions Aqueous acid solutions (aq)(aq) conduct electricity. conduct electricity.

• Have a bitter taste.Have a bitter taste.

• Feel slippery. Many soaps contain bases.Feel slippery. Many soaps contain bases.

BasesBases

• Cause color changes in plant dyes.Cause color changes in plant dyes.

• Aqueous base solutions Aqueous base solutions (aq)(aq) conduct electricity. conduct electricity.

ammoniaammoniahydroxide ionhydroxide ion

(“milk of magnesia”)

acid - a hydrogen ion donorbase - a hydrogen ion acceptor

acid base

A hydrogen ion, H+, is the same as a proton!

Hydronium ion, hydrated proton, H3O+

Electron-rich region

Electron-poor region

Figure 13.3

HH

HHHH

OO

acidbase

acid - a hydrogen ion donorbase - a hydrogen ion acceptor

acid base

Neutralization Reaction

acid + base salt + water

HCl (aq) + NaOH (aq) NaCl (aq) + H2O

SaltsSalts

HCl (aq) + KOH (aq) KCl (aq) + H2O

Solutions: Acidic, Basic or NeutralNeutral

HCl (aq) + H2O (l) → Clˉ (aq) + H3O+ (aq)

acid base

acidbase

NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OHˉ (aq)

Water is amphoteric – can behave as an acid or base

How do we express the concentration

of an acid or a base?

pH scale – based on concentration of the

hydronium ion (H3O+)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

acidic basicneutral

Based on powers of 10:

e.g., a soln with pH = 3 is 10 times moreacidic than a solution with pH = 4

Common substances that are acidic

pH Values of Some Common Solutions

Red Cabbage Juice Used to Determine pH

Oxidation-Reduction (Redox) Reactions(electron transfer reactions)

2Na (s) + Cl2 (g) 2NaCl (s)

2Na 2Na+ + 2e-

Cl2 + 2e- 2Clˉ

Oxidation half-reaction (lose e-)

Reduction half-reaction (gain e-)

2Na + Cl2 + 2e- 2Na+ + 2Cl- + 2e-

2Na + Cl2 2NaCl

2Na (s) + Cl2 (g) 2NaCl (s)

Na is the reducing agent

Cl2 is the oxidizing agent

Reducing agentsReducing agents(be oxidized)(be oxidized)

Oxidizing agentsOxidizing agents(be reduced)(be reduced)