Acids And Bases Part 1 Flashcards
What does bronsted Lowry theory describe acids and bases in terms of
Protons
What does an acid-base reaction involve
Proton transfer
Acid
A substance that donates H+ ions
What are acids classified as strong or weak depending on
The extent of dissociation
Strong acid
Completely dissociates in solution
Weak acid
Partially dissociates in solution
Base
A substance that accepts H+ ions
Alkali
A base that releases hydroxide ions in aqueous solution
What type of reaction is that of acids with metals
Redox
What is the role of H+ ions in the reaction of acids with metals
Oxidising agent
What are acid base equilibria
Reversible reactions involving the transfer of protons
pH
-log[H+]
What does a low pH mean
Larger concentration of H+ ions
What does a high pH mean
A small concentration of H+ ions
[H+]
10 ttp -pH
How many moles of H+ ions does one mole of a monoprotic acid donate
One mole
What do you assume in pH calculations for strong acids
Complete ionisation
What does it mean that for pH calculations of strong acids, you assume complete ionisation
[H+]=original conc of acid
Is sulfuric monoprotic
Diprotic
[H+]=2[HA]
What are a weak acids undissociated molecules in equilibrium with
It’s ions
Acid dissociation constant
Ka
Ka
Conc product/conc reactants
Units of Ka
Moldm-3
What is the value of Ka a quantitative measure of
The strength of a weak acid
What is the relationship between degree of dissociation and Ka value and why
Greater degree of dissociation, higher conc of H+ and larger Ka value
What is pKa sometimes used for
To compare the relative strengths of acids
pKa
-logKa
Relationship between Ka value and strength of acid
Higher Ka value = stronger acid
Relationship between pKa value and acid strength
Lower pKa value = stronger acid
Expression for ionisation of water
h20 > H+ + OH-
To what extent does pure water ionise to
A very small extent
What is Kw derived from
The equilibrium constant for the dissociation of water into H+ ions and OH-
Definition of Kw
[H+][OH]
What is Kw at 298K
1x10-14 mol2dm-6
Why is the dissociation of water an endothermic process
Energy is required to break bonds
Why does Kw increase when temperature increases
The equilibrium moves to the right
Assumptions to make to calculate the pH of a strong base
- assume complete ionisation
- assume Kw= 1x10-14