Acids and Bases

Question 1

What is the oxonium ion?

Answer 1

H₃O⁺

Question 2

What is an Arrhenius acid?

Answer 2

An acid which ionize in water to give H⁺ and anions in water.

Question 3

What is an Arrhenius base?

Answer 3

A base which ionizes to give OH^- ions and cations in water.

Question 4

What is a Brønsted-Lowry acid?

Answer 4

An acid that donates H⁺ ions in a reaction.

Question 5

What is a Brønsted-Lowry base?

Answer 5

A base that accepts H⁺ in a reaction.

Question 6

What is a Lewis acid?

Answer 6

A lone pair acceptor.

Question 7

What is a Lewis base?

Answer 7

A lone pair donor.

Question 8

What process and property does water have?

Answer 8

Autoionisation and amphoteric.

Question 9

What is the reaction of boronic acid, B(OH)₃ with water?

Answer 9

B(OH)₃ + 2H₂O -> H₃O⁺ + B(OH)₄^-

Question 10

State the strength of the conjugate base of a weak acid.

Answer 10

Strong

Question 11

How can a greater distinction between the strength of strong acids be made?

Answer 11

If water is being used as the solvent, solvent levelling will occur. For greater distinction, use a weak acid which is harder to acidify.

Question 12

When can we not assume [H₃O⁺]=[A^-]?

Answer 12

When in very dilute solution

Question 13

What assumption can me made for very weak acids in the K_a equation?

Answer 13

[HA]_initial=[HA]_final, using [HA]_initial-[H₃O⁺] will be more accurate.

Question 14

How do you work out the degree of dissociation?

Answer 14

([H₃O⁺]/[HA]_initial)x100

Question 15

What is the equation relating K_a, K_b and K_w?

Answer 15

K_a+K_b=K_w(=14@298K)

Question 16

What is the trend for the acidity of the hydrogen halides and what are the 2 reasons this trend occurs?

Answer 16

HI>HBr>HCl>HF

1. The H-X bond becomes weaker down the group
2. The stability and reactivity of X^-, the higher the charge density of X^-, the more stable it is in water(favouring F^-) but if it has a high charge density, it can stop H₃O⁺ moving freely so it lowers the acidity

Question 17

What 2 features to oxo acids have?

Answer 17

O-H and E=O bonds

Question 18

If an oxo acid is dibasic what does the structure contain?

Answer 18

2 O-H groups

Question 19

What is Bell’s rule?

Answer 19

For the acid H_mEO_n, pKa_~8-5(n-m) n-m denotes the number of E=O groups

Question 20

How do halogenated organic acids compare in acidity to regular organic acids and why?

Answer 20

Halogenated organic acids are more acidic as halogens are electronegative which draws electron density towards it and makes carbons partially positive so a negative charge of a conjugate base is better stabilised.

Question 21

What process can happen to Fe(OH)₃(OH₂)_3(s)?

Answer 21

It can be dehydrated to Fe₂O_3(s)

Question 22

Why is hydrated Al³⁺ a weaker acid than hydrated Fe³⁺?

Answer 22

Transition metals make stronger metal-oxygen bonds than other metals and the conjugate bases of iron can dimerise, increasing its stability.

Question 23

What are the 2 products of Al₂O₃ reacting amphoterically?

Answer 23

[Al(OH)₄]^- and [Al(OH₂)₄(OH)₂]⁺

Question 24

What is the Henderson-Hasselbach equation?

Answer 24

pH=pK_a+log([A^-]/[HA])

Question 25

What is a back titration?

Answer 25

Where you react a substance with an excess of acid/base, then react the remaining acid/base to work how much is left and therefore how much of the substance there was.

Question 26

What will a weak acid/strong base titration graph look like and where is the equivalence point? Why is there a change in the pH of the equivalence point?

Answer 26

The lower half of the graph will move up with an equivalence point pH\>7. When the acid has been neutralised the strong conjugate base remains in solution, making the solution basic

Question 27

How do you find the equivalence pH of successive ionisations of an acid?

Answer 27

Find the average of the 2 pK_a values

Question 28

If an indicator is represented as HIn, when would you expect the colour of the solution to change? When does the colour actually change?

Answer 28

When [HIn]=[In^-], at pH=pK_in. When there is a 10:1 ratio of one form to the other form, this means the pH usually changes over 2 pH units.

Question 29

For amino acids, what is pI occur? How can this be tested?

Answer 29

The pH when an amino acid is favoured as the zwitterion with no charge. This can be tested with electrophoresis.