IB SL Chemistry - Reactivity 3.1

Arrhenius acid

Dissociates in water to form hydrogen ions [H⁺]

Arrhenius base

Dissociates in water to form hydroxide ions [OH^-]

What is an Arrhenius neutralization?

H⁺ + OH^- → H₂O

What are two limitations of Arrhenius acid & base classifications?

1) They must be soluble in water or no ions will be produced in aqueous solutions and 2) some bases (like NH₃) do not contain oxygen and therefore can not produce OH^- by dissociation.

Brønsted-Lowry acid

A proton donor- can lose H⁺ ions

Brønsted-Lowry base

A proton acceptor- can gain H⁺ ions

Ionization

A reactions that produces ions

Dissociation

A single molecule breaks into two of more species

How does a hydronium ion [H₃O⁺] form?

H⁺ + H₂O → H₃O⁺, where oxygen donates a lone electron pair to H⁺ to create three O-H bonds, forming a trigonal pyramid.

True or False: All acid-base processes in aqueous solutions involve hydronium ions rather than isolated hydrogen protons.

True

Describe the characteristics of the collective name “alkali”

Water-soluble bases, such as hydroxides of groups 1 and 2 metals.

Conjugate acid-base pairs

The acid-base pair in which the species differ by exactly one proton.

True or False: The same species can not act as a Brønsted-Lowry base in one process and as a Brønsted-Lowry acid in another.

False. Example: H₂SO_4(aq) → 2H⁺ + SO₄^2-_(aq). Hint: Organize the equations for a two-step dissociation to find the conjugate pairs.

Amphoteric

Species that can react with both acids and bases (and therefore have both properties).

Amphiprotic

Species that can both accept or donate a proton.

True or False: Amphiprotic species are always amphoteric, but not all amphoteric species are amphiprotic.

True

Is water a Brønsted-Lowry acid or base?

Depends on the reaction! Water can act as both.

2-Amino Acids

Amphiprotic organic compounds with the general formula H₂N-CH(R)-COOH. (Where R is a hydrocarbon or other organic substituent.)

Zwitterions

A molecule that carries both a positive and a negative charge, but has a net charge of zero. Example: In a neutral aqueous solution, 2-amino acids exist as zwitterions.

How do zwitterions act in acid or base solutions, respectively?

Acidic solution: The zwitterion acts as a Brønsted-Lowry base by accepting a proton and producing cations.

Basic solution: The zwitterion acts as a Brønsted-Lowry acid by losing a proton and producing anions.

What is the equation for the potential of hydrogen, pH?

pH = -log[H⁺] or [H⁺] = 10^-pH

True or False: The higher the pH, the more acidic the solution is.

False

What is the ionic product of water and its equation?

The equilibrium constant for the self-ionization of water: K_w = [H⁺][OH^-].

What is the value of the K_w at room temperature (25^oC or 298K)?

K_w = 1.00 × 10^-14

True or False: K_w only applies to dilute aqueous solutions, so the equilibrium concentration of water is approximately 55.5 mold dm^-3.

True

True or False: When the value of K_w remains constant, [H⁺] = [OH^-] = (1.00 × 10^-14)^1/2 = 1.00 × 10^-7 mol dm^-3, therefore, for every 55.5 mol of water, only 1.00 x 10^-7 mol exists as ions.

True

True or False: In basic solutions, the concentration of H⁺ ions will always be greater than OH^- ions.

False

Exchangeable hydrogen atom

A weakly bonded hydrogen atom that can detach from the rest of the molecule because of its highly polar bond that gives H a slight positive charge. It usually forms bonds with highly electronegative atoms.

Acid residue

When the hydrogen atom dissociates (forms H⁺) and the rest of the atom produces an anion.

Oxoacids

Inorganic acids that contain oxygen.

What does the stem “-protic” mean?

One, two or three exchangeable hydrogen atoms.

True or False: Organic molecules contain bth exchangeable and nonexchangeable hydrogen atoms.

True

Name the 7 strong acids

Hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogen iodide (HI), nitric (HNO₃), sulfuric (H₂SO₄), perchloric (HClO₄), and chloric (HClO₃).

True or False: Strong acids do not dissociate completely in aqueous solutions, but it is an irreversible reaction.

False and then true- strong acids dissociate completely in aqueous solutions, but then because of that, the reversible reaction is not possible.

True or False: The strength of oxoacids (generally) increase with the oxidation state of the central atom.

True- higher oxidation = more oxygen atoms.

What are binary acids and their trend?

Acids that consist of only two elements. Their strength increases across a period and down a group.

True or False: When dissociating more than one hydrogen atom, the greater the number of hydrogen atoms to pull apart, the amount of energy exerted decreases.

False- the amount of energy exerted increases because the electrostatic attraction between the ions are much greater in the second dissociation step, compared to the first.

Metal hydroxides

(Strong) inorganic bases that contain a metal atom and one or more OH group.

What are the two exceptions to ionic hydroxides that are not readily soluble in water?

Mg(OH)₂ and Ca(OH)₂

Covalent hydroxides

A metal atom and the oxygen of the OH group are linked together by a polar covalent bond. These are weak bases and virtually insoluble in water.

True or False: Ammonia (NH₃) is not an inorganic base since it does not contain a metal.

False- Ammonia is one of the few inorganic bases that does not contain a metal. It acts as a weak Brønsted-Lowry base by accepting a proton from an acid or water.

True or False: Aqueous ammonia is often just represented as ammonium hydroxide (NH₄OH), which is unstable and exists only in solutions.

True

True or False: The dissociation of a weak acid is a favorable process.

False- Only a small portion of the acid exists as ions while most of the weak acid molecules remain undissociated.

True or False: When the reaction involves two weak acids, the the equilibrium of the reaction will be shifted towards the weak acid (as a molecule, undissociated).

True

What are the products in a reaction between an acid and active metals?

A salt and H₂ gas

Spectator ions

Ions that do not participate in the reaction

What is the difference between a total ionic equation and a net ionic equation?

Total: all ions are present.

Net: all active ions, not the spectator ions.

True or False: Strong and weak acids can be compared by their rates of reaction as long as the concentrations of each solution are equal.

True

What are the products in a reaction between an acid and metal oxides?

A salt and H₂O_(l) - can be classified as neutralization reactions because the acid acts as as Brønsted-Lowry base.

What are the products in a reaction between an acid and metal carbonates (Ex: Na₂CO₃) or an acid and metal hydrogencarbonates (Ex:NaHCO₃)?

A salt and carbonic acid, H₂CO₃. However, carbonic acid quickly decomposes into water and carbon dioxide.

Antacids

Weak bases that neutralize the excess acid.

What are the two side effects of antacids?

1) the CO₂ produced causes bloating and belching + 2) the intake of metal ions disturbs the balance of electrolytes in the body.

What is one way to identify the parent acid and base for a particular salt?

To split the salt into cation(s) and anion(s)

What is the purpose of a titration?

To find the unknown concentration of an acid or base in a solution.

What are the x and y-values on a pH curve?

pH values collected VS added volume of the standard solution

Analyte

The analyzed substance with unknown concentration.

Titrant

The reactant added to the analyte or a standard solution of that reactant

What is the difference between the equivalence point and the endpoint of a titration?

The equivalence point is the point at which the number of moles of the titrant added is exactly equal to the number of moles of the analyte in the solution being analyzed. The endpoint is the point at which the indicator changes color, signaling the completion of the reaction