8 acid bases and salts

Question 1

theories of acids and bases (3)

Answer 1

Arrhenius’ theory of acids and bases
Brønsted-Lowry theory of acids and bases
Lewis theory of acids and bases

Question 2

define Arrhenius’ theory of acids and bases

Answer 2

an acid is a substance that has H in its formula and releases H+ ions when dissolved in water
HNO3 (aq) -> H+ (aq) + NO3- (aq)

a base is a substance that has OH in its formula and releases OH- ions when dissolved in water
NaOH (s) -> Na+ (aq) + OH-(aq)

Question 3

limitations of arrhenius theory

Answer 3

• the definition of Arrhenius acids and bases is confined to those acid-base reactions that occur in aqueous solutions. however, there are many reactions which appear to be acid-base reactions that occur in other mediums. For example, the reaction between gaseous hydrogen chloride and ammonia gas can be considered as an acid -base reaction (as it produces a salt)
• a major shortcoming of the Arrhenius acid-base definition: many substances that release OH- ions when they dissolve in water do not contain OH in their formulas. This theory did not account for the basic properties of ammonia and some organic substances (such as amine) that do not contain the OH group
  thus relatively few species have these structural prerequisites ad arrhenius acid-base reactions are relatively few in number.

Question 4

define the Brønsted-Lowry theory of acids and bases

Answer 4

an acid is a substances that can donate a proton (H+) to another substance (proton donor)
a base is a substance that can accept a proton (H+) from another substance (proton acceptor)

Question 5

define a Brønsted-Lowry reaction

Answer 5

involved the transfer of a proton from the acid (proton donor) to the base (proton acceptor). an acid and base always work together in the transfer of a proton. In other words, one species behave as an acid while the other species behaves as a base simultaneously.

HNO3 (aq) + H2O (l) -> H3O+ (aq) + NO3- (aq)
acid base.

hydronium ions (H3O+) are hydrated protons in solution

in the reaction
HNO3 + H2SO4 -> H2NO3 + HSO4-
base. acid. accepts. donates

using the brønsted-lowry theory, nitric acid, HNO3 can either be Brønsted-lowry acid or base.
w strong acid - base
w alkali - acid

Question 6

pro of brønsted-lowry

Answer 6

the basic properties of substances that do not contain the OH group in its formula such as NH3 can be accounted for: NH3 is a base which accept a proton (H+) from HCl to from NH4+ in the acid-base reaction.

Question 7

conjugate acid and base

Answer 7

acid becomes conjugate base after losing a proton
acid + H2O <=> conjugate base + H3O+

base becomes conjugate acid after accepting aproton
base + H2O <=> conjugate acid + OH-

brønsted-lowry reaction:
acid + base <=> conjugate base + conjugate acid

(ONE PROTON ONLY)
H2SO4 -> HSO4- + H+ -> SO4^2- + 2H+

Question 8

define amphiprotic species (and example）

Answer 8

amphiprotic species are substances that can act both as a brønsted-lowry acid and as a brønsted-lowry base.

e.g. water, polyprotic species like H2PO4-

H2PO4- + OH- <=> HPO4^2- + H2O
(acid)
H2PO4- + H3O+ <=> H3PO4 + H2O
(base)

Question 9

lewis theory of acids and bases

Answer 9

an acid is a substance that can accept a pair of electrons from a base to form a dative covalent bond (acid is an electron-pair acceptor) (electron deficit)
a base is a substance that can donate a pair of electrons to an acid to form a dative covalent bond (base is an electron pair donor) (electron rich)

Question 10

product of lewis acid-base reaction is called:

Answer 10

an adduct, a single species that contains a new dative covalent bond.

Question 11

benefits of lewis definition

Answer 11

greatly expands the classes of acids. many species that do not contain H in their formula (and thus cannot be Brønsted-lowry acids by donating protons can function as Lewis acids by accepting an electron pair in their reactions.

Question 12

lewis > brønsted-lowry > arrhenius

Answer 12

scope of definition

Question 13

properties of acids (6)

Answer 13

sour
pH of 1-7 (only at 25degcel)
reacts with base to form salt and water
reacts with carbonates to form salt, carbon dioxide and water
reacts with metals to form salt and hydrogen
releases hydrogen ions (H+) when dissolved in water

Question 14

chemical reactions of acids

Answer 14

acid + metal -> salt + hydrogen gas
acid + carbonate -> salt + water + carbon dioxide
acid + base -> salt + water