Acid-Base And pH (w4)

Question 1

pKa shows …

Answer 1

How strong an acid is

Question 2

Strong acid =

Answer 2

Completely ionised in water

Question 3

pH =

Answer 3

-log10[H+]

Question 4

Strong base =

Answer 4

Completely dissociated

Question 5

Kw = 1 x 10^(-14)
Kw =

Answer 5

[H+][OH-]

Question 6

Weak acids =

Answer 6

Don’t completely ionise in water.
The amount of ionisation is governed by the equilibrium.

Question 7

pKa?

Answer 7

The pH at which it is exactly half dissociated.

Question 8

If pH is increased (more basic) ?

Answer 8

The acid will become more ionised, pH > pKa dissociated.

Question 9

If pH is lowered (more acidic) ?

Answer 9

The acid becomes less ionised, pH < pKa undissociated.

Question 10

Ratio of ionised: non-ionised forms …

Answer 10

A shift in pH by one unit to either side of the pKa value must change the ration by a factor of 10.

Question 11

Outline an equation for a neutralisation reaction …

Answer 11

ACID + BASE —> SALT + WATER

Question 12

What does salt hydrolysis usually effect ?

Answer 12

The pH of a solution

Question 13

Strong acid + strong base =

Answer 13

Neutral salt
PH = 7

Question 14

Strong acid + weak base =

Answer 14

Acidic salt
pH <7

Question 15

Weak acid + strong base =

Answer 15

Basic salt
pH >7

Question 16

Weak acid + Weak base =

Answer 16

Dependant on which one is stronger

Question 17

Weak acid + weak base concepts :

Answer 17

• Ka cation > Kb anion = acidic solution
• Kb anion > Ka cation = basic solution
• if Ka and Kb are similar the solution is close to neutral.

Question 18

What is the half equivalence point ?

Answer 18

The half point - the half of the total amount of base (added) needed to neutralise the acid it has been added to.
PH = pKa of the weak acid

Question 19

What us the equivalence point ?

Answer 19

The end point of the reaction = there are equal stoichiometric amounts.
The reaction has completed as all the acid has been converted to its conjugate Base.

Question 20

What is an acid-base titration (neutralisation) ?

Answer 20

The quantitative analysis of the concentration of an unknown acid or base solution.

Question 21

What us a buffer solution ?

Answer 21

A solution which is able to resist changes in pH on addition of small amounts of acid or base.

Question 22

Define buffer capacity ….

Answer 22

The number of moles per litre of a strong acid or base required to produce an increase or decrease of one pH unit in the solution.

Question 23

IN CLASS TEST ;
What is the pH of a buffer solution containing 0.042M NaH2PO4 and 0.058M Na2HPO4 ?

Answer 23

HINT
Use the Henderson-Hasselbalch equitation;
PH = pKa + log10 x ([A-]/[HA-])

Figure out which one is the base [A-]
And which is the acid [HA-]

Question 24

What do we do to move the pH of the buffer solution up by one unit of pH = pKa ? (More basic)

Answer 24

We need to insure the ionised form is 10 times higher.

Question 25

Dibasic acid =

Answer 25

2 ionisable groups

Question 26

Tribasic acid =

Answer 26

3 ionisable groups

Question 27

Ionisable groups ;

Answer 27

Some acids have more than one ionisable group this means more than one H+ is released.

Question 28

Is it more difficult to lose a H+ from an anion or uncharged molecule ?

Answer 28

It is more difficult to lose a H+ form and anion.

Question 29

What do basic oxides react with ?

Answer 29

Acids

Question 30

What to acid oxides react with ?

Answer 30

Bases

Question 31

What to amphoteric substances react with ?

Answer 31

Both acids and bases

Question 32

What happens when there are more double bonded oxygens in a molecule ?

Answer 32

The more acidic it will be

Question 33

Why does acidity increase as number of double bonded oxygens increase ?

Answer 33

There is more resonance forming so greater e- delocalisation making a more stable conjugate base.

Question 34

How do you know a reaction is completed ?

Answer 34

All the acid has been converted to its conjugate base

Question 35

What does it mean if there is a large pKa difference ?

Answer 35

The reaction is irreversible

Question 36

What happens to H20 in an aqueous solution ?

Answer 36

The H2O will donate the H+ to any base stronger than OH-

Question 37

What do amphiprotic compounds act as ?

Answer 37

They act as a proton donor and as a proton acceptor

Question 38

What do amphoteric compounds function as ?

Answer 38

Either an acid or base depending upon conditions it is in.

Question 39

What is an amino acid ?

Answer 39

And amphoteric compound, contains separate acidic and basic groups

Question 40

What is the isoelectric point (pI) ?

Answer 40

The pH at which concentration of the zwitterion is maximum Or pH at which the concentrations of cationic and anionic forms are equal.

Question 41

When are amino acids positively charged, negatively charged and neutral ?

Answer 41

- positively charged at low acidic pH - negatively charged at high basic pH - NEUTRAL (zwitterionic) at neutral pH (7)

Question 42

What’s are some properties of an ionised species ?

Answer 42

- very low lipid solubility - unable to permeate through membranes - only non - ionised drug is usually able to cross membranes

Question 43

Give an example of a compound commonly used to prepare buffers for biochemical experiments …

Answer 43

Glycine