Brønsted lowry Flashcards
What is a B-L Acid
A proton donor (the H+ must have a slight +)
What is a BL Base
A proton acceptor, must have a lone pair that can be used to form a dative covalent bond with proton
What is a conjugate base pair?
An Acid is a base with a hydrogen attached a Base is an acid with the hydrogen removed.
Is water an acid or a base?
Both! Water can be an acid donating H+ to form OH-, or it can be a base accepting H+ to form H3O+!
How do we show complete dissociation from partial dissociation
Complete as a single arrow
Partial has a reversible one
What is the difference between strong acids and weak acids?
Strong fully dissociate where weak only partially dissociates.
Examples of strong Acids?
HCl, HNO3, H2SO4 etc (inorganic)
Example of weak?
Organic
What is the formula for ph?
Ph= -log[H+]
How do we calculate mol H+ when we know the conc of a strong acid?
Monoprotic! So 1mol/dm3 = 1 mol H+ per dm3
What does Ka tell us?
Large Ka = large dissociation .^. Strong acid
Lil Ka = lil dissociation .^. Weak acid
What is Ka for weak acids?
Ka= [H+]^2 / [HA]
What is Kw?
Dissociation of water has a set value at set temp.
How do we work our ph of strong base?
Use Kw! Will be given in the question! Kw= [H+] x [OH-] As strong base dissociates fully, [OH-] we know [H+]= Kw / [OH-] The use Ph formula
How do we compare strength?
Use eqimolar samples at same Temp. And measure ph.
Titrations Acid and base, if acid and base have similar Ka/Kp etc then resulting salt will be neutral but weak acid strong base or strong base weak acid then ph will shift.
How do we determine Ka?
Make up a standard solution Use calibrated ph meter to read Calc mol Acid and conc Use ph to calc H+ Calc Ka
What is the equivalence point?
When the acid and base have reacted together in exactly the same amounts according to the stoichiometric equation. The ph at this point depends on the comb of acid and base used.
Sources of error in experiments
Assuming HA i = HA eq
Transfer errors in weighing and dissolving
Ph measurement!
What happens to an indicator when [H+] is increased?
Equil. Goes left and conc HIn goes up
What happens when we increase [OH-]?
Equil goes Right, as H+ decreases H2O formed and so less HIn formed.
How do we work out when the transition colour will be seen?
KIn! =[H+] [In-] / [HIn]
When [HIn] = [In-] KIn .^. = [H+]
And then work our Ph!
What is a buffer?
A solution of a constant Ph that is resistant to ph changes.
How do buffers work?
They contain a weak acid which only partially dissociates in water producing a large conc. of conjugate acid and a small conc of conjugate base. To this we add conjugate base salt that fully dissociates in water. This produces a pot of conjugate acid and one of conjugate base which allows the solution to react to small additions of acids and bases.
How do we calc the ph of a buffer?
From Ka calc we make [H+] the subject Only a small amount of HA dissociates therefore [Ha] In =[HA] eq The salt is ionic so fully dissociates Then work out ph [H+] = ka x [acid]/ [base]
