Unit2-Acids and Bases Test Flashcards
Operational definitions
a list of properties of operations that can be performed to identify a substance
Operational definitions for Bases
BASES
- pH>7
- taste bitter
- no reaction with active metals
- feel slippery
- red litmus turns blue
- no reaction with carbonates
- conduct electric current
- neutralizes acids to water and a “salt”(ionic compound)
Arrhenius Theory
Acid-any substance that dissociates or ionizes in water to produce H+ ions ie an acid must contain H+ ions
Ex. HCl (aq) –> H+(aq) + Cl-(aq)
Base -any substance that dissociates in water to produce OH- ions ie. base must contain OH- ions
ex. NaOH(aq)—> Na+(aq) + OH- (aq)
The limitations of the Arrhenius Theory
1. H+ cannot exist as an ion in water
The positive H+ ions are attracted to the polar water molecules forming Hydronium ions or H30 (aq)
H+ (aq) + H20(l)—> H30+ (aq)
- CO2 dissolves in water to produce an acid
NH3 dissolves in water to produce a base
Neither of these observations can be explained by the theory - Some acid-base reactions can occur in solvents other than water. Arrhenius theory can explain only aqueous acids or bases
- Arrhenius theory is not able to predict whether certain species are acids or bases
EX. NaHSO4 ,H2P04- , HCO3-
Modified Arrhenius Theory
Acid- any substance that reacts with water to produce H3O+ions
ex. HCl(g)+ H20(l) —> H30+(aq) + Cl(aq)
Base- any substance that reacts with water to produce OH- ions
Ex. NH3 (aq) +H20 —> NH4+ (aq) +OH-
Bronsted-Lowry Theory (BLT)
Acid-any substance form which a proton(H+) may be removed
ie. an acid is a substance that loses a proton (H+)
(any donor)
Base- any substance that can remove a proton (H+) from an acid
ie. a base is a substance that gains a proton (H+)
In BLT, an acid-base reaction requires the transfer of a proton (H+) from an acid to a base.
What is a conjugate acid-base pair?
(Page 554)
Two particles that differ by one proton are called a conjugate acid-base pair
The conjugate base forms when an acid loses its proton
The conjugate acid forms when a base gains a proton (H+)
Amphoteric substance
an amphoteric substance can be either an acid or a base. Usually negative ions that contain at least one hydrogen atom
Strong acid
A strong acid is an acid that ionizes or dissociates 100% in water
Ex. HCl(aq)—> H+ (aq) + Cl-(aq)
OR strong acids react 100% with water (BLT)
HCl(aq) + H20—> H30+ (aq) + Cl-(aq)
Note: Strong acids produce more H+ ions or more H30+ ions than weak acids with the same molar concentration
-The equilibrium symbol is NOT used for strong acids because there is NO REVERSE REACTION
Weak acid
An acid that ionizes or dissociates LESS than 100%
For weak acids a equilibrium is established between the original acid molecule and the ions formed.
ex. HF(aq) ⇌ H3O +(aq) + F-(aq)
monoprotic
acids that contain or lose one proton
diprotic
acids that contain or lose two protons
polyprotic
any acid with more than one proton
Strong Base
is a base that dissociates 100% in water, or reacts 100% with water to produce OH- ion
- the only strong bases are hydroxide compounds of most Group 1 and Group 2 elements
ex. NaOH—> Na+ (aq) +OH-(aq)
Weak base
is a base that reacts less than 100% in water to produce OH- ion
S2- +H20 ⇌ H30+(aq) + F-(aq)
STEPS FOR WRITING BLT ACID-BASE EQUATIONS
STEP 1 : list all molecules/ions present
- ionic compounds dissociate
- strong acids exist as hydronium ion and the anion (conjugate Base)
- Weak acids use the full acid formula
- always include water in the list
STEP 2: identify the strongest acid and the strongest base from Step 1
STEP 3: write the equation for the reaction by transferring a proton from the strongest acid to the strongest base.
STEP 4: Determine the type of reaction arrow to use in the equation
-Hydronium (H30+) and bases stronger than nitrate
-Hydroxide (OH-) and acids stronger than hypochlorous acid (HCl)
STEP 5: determine the position of equilbrium by comparing the strengths of the acids in the equation.
The favoured side is the side with the weaker acid
