Unit 12 - Acid/Base Chemistry and Titrations

Introduction:

Acid and bases can be defined in terms of hydrogen ions and hydroxide ions or in terms of electron pairs. The topic of acids and bases can be branched off further into much deeper topics that are beyond the scope of this course.

Student Objectives - Unit 12

13.1

a. Acids have a sour taste and react with active metals. Acids change the colors of acid-base indicators, react with bases to produce salts and water, and conduct electricity in aqueous solutions.

b. Bases have a bitter taste, feel slippery to the skin in dilute aqueous solutions, change the colors of acid-base indicators, react with acids to produce salts and water and conduct electricity in aqueous solutions.

c. An Arrhenius acid contains hydrogen and ionizes in aqueous solution to form hydrogen ions. An Arrhenius base produces hydroxide ions in aqueous solution.

d. The strength of an Arrhenius acid or base is determined by the extent to which the acid or base ionizes or dissociates in aqueous solutions.

13.2

a. A Bronsted-Lowry acid is a proton donor. A Bronsted-Lowry base is a proton acceptor.

b. A Lewis acid is an electron-pair acceptor. A Lewis base is an electron-pair donor.

c. Acids are described as monoprotic, diprotic or triprotic depending on whether they can donate one, two or three protons per molecule, respectively, in aqueous solutions. Polyprotic acids include both diprotic and triprotic acids.

13.3

a. In every Bronsted-Lowry acid-base reaction, there are two conjugate acid-base pairs.

b. A strong acid has a weak conjugate base; a strong base has a weak conjugate acid.

c. Proton-transfer reactions favor the production of the weaker acid and weaker base.

d. The acidic or basic behavior of a molecule containing –OH groups depends on the electronegativity of other atoms in the molecule and on the number of oxygen atoms bonded to the atom that is connected to the –OH group.

e. A neutralization reaction produces water and an ionic compound called a salt.

f. Acid rain can create severe ecological problems.

14.1

a. Pure water undergoes self-ionization to give 1.0 x 10-7 M H3O+ and 1.0 x 10-7 M OH- at 25oC.

b. pH = -log[H3O+]; pOH = -log[OH-]; at 25oC, pH + pOH = 14.0.

c. At 25oC, acids have a pH of less than 7, bases have a pH of greater than 7 and neutral solutions have a pH of 7.

d. If a solution contains a strong acid or a strong base, the [H3O+], [OH-] and pH can be calculated from the molarity of the solution. If the solution contains a weak acid or a weak base, the [H3O+] and the [OH-] must be calculated from an experimentally measured pH.

14.2

a. The pH of a solution can be measured using either a pH meter or acid-base indicators.

b. Titration uses a solution of known concentration to determine the concentration of a solution of unknown concentration.

c. To determine the endpoint of a titration, one should choose indicators that change color over ranges that include the pH of the equivalence point.

d. When the molarity and volume of a known solution used in a titration are known, then the molarity of a given volume of an unknown solution can be found.Ohio Department of Education - Chemistry Standards:

Acid-base chemistry is not explicitly listed in the Ohio standards for chemistry.

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