[Chemistry I] Lesson 7: Acids and Bases

Memorization: List the strong acids.

"ClNOSO, ClO ClO BrI" HCl HNO3 H2SO4 HClO3 HClO4 HBr HI

What is the gram equivalent weight of phosphoric acid?

32.7g H3PO4 has 3 acid equivalents (3 mol H+). Therefore, to find the gram equivalent weight, first find the mass of H3PO4 and divide by the number of equivalents. 98.0g/3 ~ 32.7g

On the MCAT, _____ are likely to be weak bases. (A) amines (B) hydroxides (C) amides (D) carboxylates

A

Match the following statements to the acid/base model they correspond to: (A) "An acid is a proton donor." (B) "In solution, acids always dissociate to leave behind excess H+, while bases always dissociate and leave behind excess OH-." (C) "A base is an electron donor."

A = Bronsted-Lowry B = Arrhenius C = Lewis

What species are considered the equivalents for acids and bases, respectively?

Acids: 1 mol H+ Bases: 1 mol OH-

Metal oxides and hydroxides can be considered: I. Amphoteric II. Amphiprotic III. Acids only IV. Bases only

I only; metal oxides and hydroxides such as Al(OH)3 are generally amphoteric (can act as either an acid or base depending on the environment) but NOT amphiprotic because they do not give off protons.

What is the value of Kw, and how does it depend on the following: I. Concentration II. Pressure III. Volume IV. Temperature

Kw = [H3O+][OH-] = 10^-14 at 298K IV only. Kw, like any other equilibrium constant, is only dependent on temperature. At temperatures above 298K, Kw increases due to the endothermic nature of the autoionization reaction.

Given a solution of 2M Al(OH)3, calculate the normality.

M = normality/n so N = M*n 2M(3 OH-'s) = 6 N Al(OH)3

Rank the following models/definitions for acids and bases in order from most to least restrictive: (A) Bronsted-Lowry (B) Lewis (C) Arrhenius

C > A > B. This implies that every Arrhenius acid/base can also be classified as a Bronsted-Lowry acid/base. Every Bronsted-Lowry acid/base can also be classified as a Lewis acid/base.

In biology and biochemistry, neutralization reactions, including the formation of peptide bonds in proteins, are often condensation reactions where a byproduct (generally H2O) is formed. The C terminus of an amino acid contains a _________ group that reacts with a ________ group on the N terminus of another amino acid. In this reaction, the __________ group serves as the acid and the _________ group serves as the base.

C terminus = carboxyl group (-COOH) that acts as a weak acid N terminus = amino group (-NH2) that acts as a weak base

True or false: A Bronsted-Lowry acid is also always a Lewis acid.

False; BF3 and AlCl3 are species that can each accept an electron pair, which qualifies them as Lewis acids, but they lack a hydrogen ion to donate, disqualifying them as both Arrhenius and Bronsted-Lowry acids.

True or false: At 30 C, a solution with a pH of 7 is considered neutral.

False; pH = 7 = neutral is ONLY valid at 25 C or 298K.

Give an example of an acid that is polyvalent AND polyprotic.

H2SO4

If the Ka of an acid is 1.8 * 10^-5, what is its pKa?

Start by taking the negative log: -log(1.8 * 10^-5) = -log(1.8) - log(10^-5) = 5 - log(1.8) Since log(n) = 0.n you move the decimal place one to the left: log(1.8) = 0.(1.8) = 0.18 Putting this together yields: pKa = 5 - 0.18 = 4.82

True or false: water is an amphoteric AND amphiprotic substance.

True; Water is amphoteric because it reacts like an acid in a basic environment and like a base in an acidic environment. It is also amphiprotic because it can either gain or lose a proton.