acids and bases Flashcards
Arrhenius
First definition (1880)
Acid: produces protons and anions in aqueous solution
Base: produces hydroxide and cations in aqueous solution.
Acid - base reactions must include the formation of one of the ions h+ or OH -
Bronsted - Lowry
Acid: proton donor
Base: proton acceptor
Acid-base reactions include the transfer of a proton from an acid to a base.
Amphoteric substances
Weak base and acid - in A reaction can be either base or acid, depends ou their environment.
How to recognize?
Must include hydrogen (for the acid) and have a lone pair (for the base)
Lewis
Acid: accept an electron pair ( lone pair )
Base: donate an electron pair ( lone pair )
Acid-base reaction include the transfer of un electron pair from a base to an acid
Naturalization reactions
A Reaction between an acid and a base that forms water (H2O) and a salt
Conjugated acid-base pairs
Conjugated Base: formed the loss of H from an acid.
Conjugated acid: formed by the addition of H to a base.
Dissociation
The process of separating charged particles which already existed in the compound.
NaCl —> Na^+ + Cl^-
Ionization
Formation of new changed particles which were not found in the compound before.
O+ 2e —> O^-2
Strong acid
Dissociate almost completely during a reaction- all of the molecules donate their proton.
Strong base
Dissociate almost completely during a reaction - all the molecules accept proton.
Weak acid/base
Dissolves partly during the chemical reaction.
Weak acid / base differ in their strength
Notice: strong/weak acid or base refer to reactivity not concentration.
The strength of conjugated pairs
The stranger the acid, the weaker it’s conjugated base
The weaker the acid, the stronger it’s conjugated base
The stranger the base, the weaker it’s conjugated acid
The weaker the base, the stronger it’s conjugated acid
Diprofic and triprotic acid
Have more than one acidic hydrogen (move than one hydrogen that can become a proton )
The dissociation of these substances is composed of several reaction
Like:H2SO4
Water auto ionization
Water = amphoteric substance
Two water molecules can preform an acid-base reaction by themselves
2H2O —> H3O + OH
Constant of water dissociation
Kw= [H3O]•[OH]= 10^-14
Applies to all aqueous solutions
The pH scale
Numerical scale used to measure the concentration of protons in a given solution, and can be used to define the solution as acidic, basic or neutral.
0-7 → acidic
7 = neutral
7-14 → basic
How to calculate pH?
pH= - log[H]
[H]= 10^-pH
example: [H]=10^-7 →pH=7
Calculation based on proton concentration derived from the concentration of the acid is possible only for strong acid, that almost completely dissolve.
What is the difference between acidity and pH values?
pH is dependent on temperature - the pH value of natural solution decreases with temp. Increase. While acidic solution will always be those in which the concentration of protons is higher than that of hydroxide ions.
pOH scale
The value of pOH indicates the concentration of OH ions, which helps to determine whether a solution is basic or not.
pOH= -log[OH]
[OH]=10^-pOH
What affects the pH values?
Strength of acid or base: strong acid or base, higher concentration of ions
Strong acid have lower pH than weak acid
Strong base have high pH than weak acid
the concentration of the solution:
more concentrated acidic solutions will have lower pH than more diluted ones.
more concentrated basic solutions will have higher pH than more diluted ones.
Universal indicators
Red → 0
Indicators
Chemical substances which are used to detect a change in the environment- used to defectacid-base reactions and distinguish between acidic and basic solutions.
They change their color based on the pH values.
Can be used as solution or absorbed by paper.
Methyl Orange
Indicator
Low pH - red
High pH - yellow
pH range → 3.2-4.4
End point -3.7
Methyl red
Indicator
Low pH - red
High pH - yellow
pH range → 4.2-6.3
End point -5.1
Bromothymol blue
Indicator
Low pH - yellow
High pH - blue
pH range → 6-7.6
End point -7
Phenolphthalan
Indicator
Low pH - colorless
High pH - pink/violet
pH range → 8.2-10
End point -9.3
Buffer solution
Reduce the change in the pH of a solution after adding an acid or a base to it- minimizing the acid or base impact (not infinite)
Acidic buffers
Keep the pH of a solution under the value of 7.
Composed of a weak acid and its salt with a strong base
Adding base will cause naturalization reaction between the added base and the weak acid, keeping the pH value as it was
Adding acid will cause naturalization reaction between the added acid and the conjugated base, keeping the pH value as it was
Basic buffer
Keep pH value above 7
Composed of a weak base and its salt with a strong acid (conjugated)
Adding base will cause naturalization reaction between the added base and the conjugated acid, keeping the pH value as it was
Adding acid will cause naturalization reaction between the added acid and the weak base, keeping the pH value as it was
Basic oxide
Metals + oxygen
Acidic oxide
Non-metals + oxygen
Al2O3
Amphoteric
BeO
Amphoteric oxide
H2O
Amphoteric
HCl
(Strong/weak acids and bases)
Strong acid
HBr
(Strong/weak acids and bases)
Strong acid
HI
(Strong/weak acids and bases)
Strong acid
HNO3
(Strong/weak acids and bases)
Strong acid
H2SO4
(Strong/weak acids and bases)
Strong acid
HClO4
(Strong/weak acids and bases)
Strong acid
Alkali (group 1) + alkaline earth (group 2) metals
(Strong/weak acids and bases)
Strong base
CO2
(Strong/weak acids and bases)
Acidic solution
SiO2
(Strong/weak acids and bases)
Acidic solution
SO2
(Strong/weak acids and bases)
Acidic solution
SO3
(Strong/weak acids and bases)
Acidic solution
