Unit 4 Equilibrium, Acids and bases

?
What is a dynamic equilibrium?
a reversible reaction where the forward and backwards reactions are equal and there concentrations are constant
1 of 44
What is a homogeneous system?
one in which all the species present and in the same phase
2 of 44
In terms of Kc how are the concentrations of the components in a reversible reaction related?
Kc=[C]^c[D]^d/[a]^a[B]^b
3 of 44
What indication of the position of equilibrium does Kc<1 give?
equilibrium will be towards the left (more reactants)
4 of 44
What indication of the position of equilibrium does Kc=1 give?
equilibrium will be in the middle (equal reactants and products)
5 of 44
What indication of the position of equilibrium does Kc>1 give?
equilibrium will be towards the right (more products)
6 of 44
How is the total pressure shown?
by the sum of the partial pressure.
7 of 44
What is Kc?
the constant for a specific reaction at a specific temperature
8 of 44
What is the only condition that will cause a change in the Kc value?
Temperature, the relationship is exponential
9 of 44
In an exothermic reaction what will raising the temperature result in?
fewer products and more reactants, hence a smaller Kc
10 of 44
In an endothermic reaction what will raising the temperature result in?
more products and fewer reactants, hence a bigger Kc
11 of 44
How does a catalyst affect the position of equilibrium and value of Kc?
Doesn't affect either as it only affects the reaction kinetics
12 of 44
What is an Acid?
a species that releases H+ and has a pH of less than 7
13 of 44
What will a base do to an acid?
neutralise it to form a salt and water
14 of 44
What is an alkali?
a soluble base
15 of 44
What are the Bronstead-Lowery definitions of Acids and Bases?
an acid is a proton donor and a base is a proton acceptor
16 of 44
What are the Lewis definitions of Acids and Bases?
an acid is an electron acceptor and a base is an electron donor
17 of 44
What is a Hydronium ion? and why does it form?
a water molecule with an extra H+ which forms because H+ions are not stable
18 of 44
How is a conjugate acid/base formed?
In a reaction between an acid and a base, the acid donates a proton to form its conjugate base and the base accepts the proton to form its conjugate acid
19 of 44
What is pH?
pH=-log[H+]
20 of 44
How do you work out the dissociation of a strong acid?
assume 100% dissociation, the value is therefore be conc of acid x mol of proton released by one mole of acid
21 of 44
How is the ionic product of water shown?
Kw=[H+][OH-]
22 of 44
How do you work out the dissociation of a mixture of acid and alkali?
calculate the number of moles of H+ from the acid and the OH- from the alkali then calculate the excess after neutralisation
23 of 44
What should be assumed about weak acids or alkalis?
they only partially dissociate
24 of 44
What is the acid dissociation constant for a weak acid?
Ka=[H+][A-]/ [HA]
25 of 44
What is a buffer solution?
one that opposes changes in pH when small amounts of acid or base are added.
26 of 44
What is an acidic buffer?
a mixture of a weak acid and its salt, maintaining a pH below 7
27 of 44
How do acid buffers work?
position of equilibrium pushed further to the left when CH3COO- are added to the weak acid resulting in excess of acid+conjugate base.Added H+ will react with CH3COO-,added base will react with CH3COOH,both are in excess pH is maintained
28 of 44
What is a basic buffer?
a mixture of a weak base and its salt, maintaining a pH above 7.
29 of 44
What does the pH of a buffer solution depend on?
the Ka value and the ration of the concentrations of the conjugate acid/base pair.
30 of 44
What is the equivalence point for an acid-base titration?
the mixing together of stoichometrically equivalent amounts of acid and base
31 of 44
At equivalence, what will the pH be for a strong acid, strong base?
exactly 7.0
32 of 44
At equivalence, what will the pH be for a strong acid, weak base?
less than 7.0
33 of 44
At equivalence, what will the pH be for a weak acid, strong base?
greater than 7.0
34 of 44
Why will weak, dipotic acids and bases produce two end points in a titration?
the the ions form separately and sequentially
35 of 44
In what ratio do the end points need to occur to allow indicators to distinguish?
1:2
36 of 44
What is the equilibria for sodium carbonate's 1st end point?
Na2CO3+H+ <=> NaHCO3 + Na+
37 of 44
What is the equilibria for sodium carbonate's 2nd end point?
NaHCO3 + H+ <=> Na+ + CO2 + H2O
38 of 44
What is an indicator?
a weak acid, whose conjugant base is a different colour
39 of 44
How does an indicator work?
adding acid moves the equilibrium to the left to form colour A, adding alkali pushes the equilibrium to the right to form colour B.
40 of 44
How is the colour change of an indicator decided?
at the end point, the conjugate base is equal to the weak acid so the pH is equal to the pKaand the pH at which the colour changes is determined by the Ka value
41 of 44
What pH range does phenolphthalein have?
8.2-10.0
42 of 44
What pH range does methyl orange have?
3.2-4.4
43 of 44
What reactions is methyl orange used for?
strong acid, weak base titrations.
44 of 44

Other cards in this set

Card 2

Front

What is a homogeneous system?

Back

one in which all the species present and in the same phase

Card 3

Front

In terms of Kc how are the concentrations of the components in a reversible reaction related?

Back

Preview of the front of card 3

Card 4

Front

What indication of the position of equilibrium does Kc<1 give?

Back

Preview of the front of card 4

Card 5

Front

What indication of the position of equilibrium does Kc=1 give?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Equilibria resources »