Acids, bases and saltes are the most common?
- electrolytes
- > a substance that dissociates into ions in solution
- it acquires the capacity to conduct electricity
What are acids?
-substances that will increase the concentration of hydrogen ions (H+) when added to solution
What are bases?
-substances that accept H+ ions -> increase the concentration of Hydroxide ions (OH-) when added to water
Is a hydroxide ion basic or acid?
-basic
How are acids and bases called if they are stron electrolytes?
-stong acids or strong bases
Why are acid-base reactions good?
- majority of reactions in organic chemistry are either acid-base reaction or involve an acid base reaction in one of the steps
- are simple, basic reactions that help the chemists:
- > show mechanisms of bond breaking or bond formation in a simple way
Give the Bronsted- Lowry definition of acids and bases
- acid -> a proton donor
- base -> a proton receiver
- molecule which forms when an acid looses a proton is called conjugated base (HBr-> Br-)
- molecule which forms when a base receives a proton is called conjugated acid (OH- ->H2O)
Name some strong acids?
which completely donate proton to water
- hydrogen iodide (HI)
- hydrogen bromide (HBr)
- sulfuric acid (H2SO4)
What happens when solid sodium hydroxide NaOH(s) is dissolved in water?
- solution composed of hydrogen and soium ions forms
- >NaOH + H2O -> Na+(aq) + OH- (aq)
What happen in the reaction of soidum hydroxide (NaOH) + hydrogen chloride (HCl)?
- NaOH + HCl = NaCl + H2O
- reaction is between hydroxide and hydronium ion
- > sodium and chlorid are called spectator ions
What is the net ionic reaction of NaOH + HCl? +
What is the net ionic reaction for all reactions between strong acid and a strong base?
- OH- + H+ -> H2O
- net ionic reaction (equation) ->lists only those species participating in the reaction
- > > H3O+ + OH- > 2H2O
Give the Lewis definiton of acids and bases
- the theory of acids-base was significantly improved by Lewis in 1923
- Lewis defined acids as receivers of an electron pair, and bases as donors of an electron pair
- > not only limited to protons, but also many other substances are acids -> aluminum chloride reacts with ammonia in the same way as a proton (AlCl3 (acid) + NH3 (base) -> [Al(NH3)Cl3]
What is also counted as a Lewis acid?
- any atom lacking an electron can act as a lewis acid
- several compound including elements of the group 3A, such as boron and aluminum, are lewis acids, Why?-> {{c1::because the elements of the group 3 A have 6 electron on their outermost shell }}
- Zinc and iron are commonly used as lewis in organic reactions
How does the reaction for a general acid (HA) in water looks like?
-HA + H2O -> KA= [H3O+] [A-|/ [HA]
. pKa = -log Ka ;as in pH = -log[H3O+]
-the bigger pKa the weaker the acid
How can you predict the strength of a base?
- stronger an acid, weaker its conjugated base
- larger the pKa of a conjugated acid, stronger is the base
What can you predict from an acid-base reaction?
-acid- base reactions always occur such that a weaker acid and a weaker base are formed
Why are weaker acid and weaker base formed?
- acid-base reactions are equilibrium reactions -> these reactions always prefer the formation of more stable (with less potential energy) compounds
- > weak acids and bases are more stable than strong acids and bases
Relationship between structure and acidity
- in the periodic table, gowing down the column, the acidity increases
- > strength of the bond with the proton -> the stronger the bond (atomic size), the weaker the acid
- in the periodic table, gowing from left to right in a row, the acidity increases –> bond strengths remains, the electronegativity of the atom bonded to hydrogen dictates the strength
How can we determine the concentration of a solution?
- we add a solution with known concentration (standard solution) to the one with unknown concentraion
- we stop the reaction at the equicalence point, where stoichiometrically equivalent quantities are brought together
- we determine this point by using dyes known as indicators
- n= V*c
Give and examaple of an acid-base titration
- NaOH used to neutralize the acid solution
- indicator: phenolphthalein -> colorless in acid solution but red in basic solution
