Chapter Menu Chapter Menu

Transcription

1 Chapter Menu Chapter Menu Section 18.1 Section 18.3 Section 18.4 Introduction to Acids and Bases Hydrogen Ions and ph Neutralization

2 Section 18.1 Intro to Acids and Bases Objectives: Compare the Arrhenius, Brønsted-Lowry, and Lewis models of acids and bases. Identify the physical and chemical properties of acids and bases. Predict and explain the final results of an acid-base reaction. Different models help describe the behavior of acids and bases.

3 Properties of Acids and Bases Properties of an Acid Acids have a sour taste. Acids react with active metals to produce hydrogen gas. (Activity series) Acids change blue litmus paper to red. Acids corrode metals. Acids react with bases to produce a salt & water in a neutralization reaction.

4 Properties of Acids and Bases Properties of a Base Bases have a bitter taste. Bases are slippery. Bases are poisonous and corrosive. (never taste or touch to identify them) Bases change red litmus paper to blue. Bases react with acids to produce a salt & water in a neutralization reaction.

5 Section 18.1 A Definition of Acids and Bases Arrhenius Acids Any compound that contains hydrogen and ionizes in aqueous solution to form hydrogen ions (H + ion) HCl(g) + H 2 O > H 2 OH + Cl - (H 3 O + ) Hydrogens are found in front of acid formula. More than one can be ionized. H 3 O + is called a hydronium ion.

6 Section 18.1 Acids and Bases Definition (cont.) Arrhenius Base Any compound that contains OH - ions and dissociates to produce OH - ions (hydroxide ions) in an aqueous solution. NaOH(s) -----> Na + (aq) + OH - (aq) OH ions are found in the second position of a base s formula.

7 Section 18.1 A Definition of Acids and Bases Categorize the following substances as Acids or Bases using the Arrhenius Definitions of Acid and Base. HCl H 3 BO 3 KOH NaOH Ca(OH) 2 HNO 3 NH 4 OH CH 3 COOH H 2 SO 4 HClO 3 Mg(OH) 2 H 3 PO 4

8 Section 18.1 The Brønsted-Lowry Model The Brønsted-Lowry Model of acids and bases states that an acid is a hydrogen ion donor, and a base is a hydrogen ion acceptor. The Brønsted-Lowry Model is a more inclusive model of acids and bases.

9 Section 18.1 The Brønsted-Lowry Model (cont.) A conjugate acid is the species produced when a base accepts a hydrogen ion. A conjugate base is the species produced when an acid donates a hydrogen ion. A conjugate acid-base pair consists of two substances related to each other by donating and accepting a single hydrogen ion.

10 Section 18.1 The Brønsted-Lowry Model (cont.) Hydrogen fluoride a Brønsted-Lowry acid HF(aq) + H 2 O(l) H 3 O + (aq) + F (aq) HF = acid, H 2 O = base, H 3 O + = conjugate acid, F = conjugate base

11 Section 18.1 The Brønsted-Lowry Model (cont.) Ammonia Brønsted-Lowry base NH 3 (aq) + H 2 O(l) NH 4+ (aq) + OH (aq) NH 3 = base, H 2 O(l) = acid, NH 4+ = conjugate acid, OH = conjugate base Water and other substances that can act as acids or bases are called amphoteric.

12 Section 18.1 Monoprotic and Polyprotic Acids An acid that can donate only one hydrogen ion is a monoprotic acid. Only ionizable hydrogen atoms can be donated.

13 Section 18.1 Monoprotic and Polyprotic Acids (cont.) Acids that can donate more than one hydrogen ion are polyprotic acids.

14 Section 18.1 Types of Acid-Base Reactions A neutralization reaction is a reaction of an acid with a base in aqueous solution to produce water and a salt. acid + base salt + water The hydronium ion (H+) and the hydroxide (OH-) ions combine chemically to form water. The anion from the acid and the cation from the base then forms a salt.

15 Section 18.1 Types of Acid-Base Reactions (cont.) What to the following produce? HCl(aq) + NaOH(aq) > H 2 SO 4 (aq) + Mg(OH) 2 (aq) ----->

16 Section 18.1 Types of Acid-Base Reactions (cont.) Salt is a general term used in chemistry to describe the ionic compound formed from the negative part of the acid and the positive part of the base.

17 Properties of a Salt Some taste salty, some taste bitter. Many dissolve well in water, others slightly, a few not at all. Salts usually form crystals Most salts are white in color. Salts are a neutral substance. (7 ph) Salts have high melting points Salts are solids at room temperature Salts are ionic compounds. Salts are good conductors of electricity when molten or dissolved in water.

18 Section 18.3 Hydrogen Ions and ph Objectives: Calculate ph, given the hydronium ion concentration. Classify solutions as acidic, basic, or neutral. ph and poh are logarithmic scales that express the concentrations of hydrogen ions and hydroxide ions in aqueous solutions.

19 Section 18.3 ph and Acids and Bases All water solutions contain hydrogen ions (H + ) and hydroxide ions (OH ). An acidic solution contains more hydrogen ions than hydroxide ions. A basic solution contains more hydroxide ions than hydrogen ions.

20 Section 18.3 ph and Acids and Bases (cont.) The usual solvent for acids and bases is water water produces equal numbers of hydrogen and hydroxide ions in a process called self-ionization. H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) The hydronium ion is H 3 O +.

21 Section 15.2 ph Concentrations of H + ions are often small numbers expressed in exponential notation. ph is the negative logarithm of the hydrogen ion concentration of a solution. ph = log [H + ] ph is the measure of the hydronium ion concentration. It indicates how acidic a solution is.

22 Section 15.2 ph (cont.) ph means the Power of Hydrogen The ph scale is 0 to represents acidic solutions (many H + ) 7 represents neutral solutions (H + = OH - ) 8-14 represents basic solutions (little H + ) The stronger the acid or base, the more extreme the ph number. Litmus paper and a ph meter with electrodes can determine the ph of a solution.

23 Section 15.2 ph problems Sample Problem #1: Calculating the ph of a solution What is the ph of a M solution of HCl, a strong acid?

24 Section 15.2 ph problems (cont.) Sample Problem #2 What is the ph of a solution if [H 3 O + ] = 3.4 x 10-5 M?