Acids and Bases

Question 1

strong acid

Answer 1

• donates high percentage of its protons to water.

- low pKa

Question 2

equivalence point

Answer 2

Point in a titration when sufficiently solution has been added to react exactly with the substance in solution in the flask.

Question 3

Are phenols or benzene rings stronger acids?

Answer 3

Phenols

Question 4

Electron donating groups on phenol _____ acid strength

Answer 4

reduces

Question 5

weak monoprotic acid.

Answer 5

Monoprotic: can donate only one proton (H+) to water.

Weak: donates very low % of protons of O-H group to water.

Question 6

Ka

Answer 6

Ka is the acid dissociation constant.

For an acid HA: Ka = [H3O+(aq)][A(aq)]/[HA(aq)]

Question 7

amphiprotic species

Answer 7

• a species which can act as both a proton donor (acid) and a proton acceptor (base). For example: HCO3-

Question 8

diprotic acid

Answer 8

can donate (up to) two protons (H+) to water.

Question 9

Explain why HO2CCH2CO2 is a weaker acid than HO2CCH2CO2H

Answer 9

HO2CCH2CO2 as a charged species loses a proton less readily

than HO2CCH2CO2H.

Question 10

triprotic acid

Answer 10

can donate (up to) three protons (H+) to water. An example is phosphoric acid, H3PO4.

Question 11

pKa

Answer 11

pKa = -log10Ka, where Ka is the acid dissociation constant. For an acid HA: Ka = [H3O+(aq)][A(aq)]/[HA(aq)]

Question 12

autoprotolysis

Answer 12

The term relates to the equilibrium constant (Kw)for D2O reacting with itself as shown in (i) above. Kw = [D3O+][OD]

Question 13

conjugate base

Answer 13

• the species remaining after a Brønsted acid has transferred a proton is the conjugate base. Cl is the conjugate base of HCl.

Question 14

autoprotolysis constant

Answer 14

• (of water, Kw) is defined by Kw = [H3O+][OH]

Question 15

equivalence point

Answer 15

The point in a titration where the exact amount of titrant has been added to react with all the compound being analysed. e.g. In the determination of ethanoic acid in vinegar the point at which the amount of base added has converted all the ethanoic acid to ethanoate.

Question 16

Explain why the hydrogen citrate ion (formed on loss of two protons from citric acid) is a weaker acid than citric acid.

Answer 16

Removing the third proton from citric acid (that is from the hydrogen citrate ion) gives a conjugate base with a higher negative charge. H+ more difficult to remove.  weaker acid

Question 17

electrophoresis

Answer 17

Electrophoresis is the separation of mixtures of amino acids based on their different isoelectric points.

Question 18

zwitterion

Answer 18

• overall neutral species formed by internal proton transfer. For example: +H3NCH2CO2−

Question 19

indicator

Answer 19

An indicator is a weak acid whose acid and conjugate base have different colours. For example: phenolphthalein

Question 20

acid rain

Answer 20

Rain with pH

Question 21

isoelectric point

Answer 21

The pH at which the majority species in solution is the zwitterion.
For example: glycine at pH 5.97 is mostly +H3NCH2CO2−

Question 22

What is meant by the term ‘buffer capacity’?

Answer 22

Ability to resist change in pH on addition of acid or base.