Acid - Base equilibria

Question 1

What is a bronsted acid

Answer 1

Proton donor

Question 2

What is a bronsted base

Answer 2

Proton acceptor

Question 3

For the reaction NH3 + H2O ⇌ NH4+ + OH- , what are the conjugate acid base pairs?

Answer 3

1. NH3 accepts a proton to become NH4+, NH3 acts as a brØnsted Lowry base
2. H2O donates a proton, thus acting as a brØnsted Lowry acid
3. NH3 and NH4+ are a conjugate acid base pair
4. H2O and OH- are a conjugate acid base pair

Question 4

What is a strong acid

Answer 4

Fully dissociates in solution, can be mono, di or tribasic

Question 5

What is mono/di basic

Answer 5

monobasic - donates 1 proton per molecule of acid

di - donates 2 protons per molecule of acid

Question 6

What is a weak acid ?

Answer 6

Partially dissociates in solution

Question 7

What is the formula for pH?

Answer 7

pH = -log[H+]

Question 8

What does [H+] equal

Answer 8

[H+] = antilog(-pH)

Question 9

Draw out the table for converting between [acid] [H+] and pH

Answer 9

on page

Question 10

What is the ionic product of water?

Answer 10

Kw = [H+][OH-]
units of mol^2dm^-6
At 25ºC , Kw = 1 x10 -14

Question 11

What is Kw in pure water?

Answer 11

in pure water [H+] = [OH-] therefore Kw = [H+]^2

Question 12

What is the table for converting between pH of strong alkalis

Answer 12

on page

Question 13

What are the equations for pKw, pOH,

Answer 13

pKw = -log Kw pKw = 14.00 at 25ºC
pOH = -log[OH-]
pH + pOH = pKw

Question 14

What is the general acid dissociation for a weak acid?

Answer 14

HA ⇌ H+ + A-

Question 15

What is Ka

Answer 15

Ka = [H+][A-]
————-
[HA]
Always has units of moldm^-3

Question 16

What does a higher Ka suggest

Answer 16

A higher Ka suggests a ‘stronger’ weak acid

Question 17

What is the table for converting between a weak acid and pH?

Answer 17

on page

Question 18

What happens when an acid or alkali is neutralised or diluted?

Answer 18

The concentration of the ions in solution changes

Question 19

What is the formula for working out concentration of a diluted solution?

Answer 19

on page

Question 20

What is the formula for working out The neutralisation

Answer 20

on page

Question 21

What is a buffer?

Answer 21

A solution that resists small changes in pH on addition of small amounts of acid or alkali

Question 22

What is the buffering action represented by?

Answer 22

HA ⇌ H+ + A-

Question 23

What is the buffering action when extra acid is added

Answer 23

1. Extra Hydrogen ions are added
2. The anion in the buffer reacts with the H+
   ( H+ + A- →HA )
3. The extra H+ ions are removed
4. This maintains [H+] and maintains pH

Question 24

What happens on the addition of alkali

Answer 24

1. Extra hydroxide ions are added
2. These react with the undissociated acid in the buffer solution (HA + OH- → A- + H2O)
3. Extra OH- ions are removed
4. This maintains [H+] and maintains pH

Question 25

What is the henderson-Hasselbalch equation?

Answer 25

on page

Question 26

Draw out the four different titration curves, state what the reaction is between and suggest a suitable indicator.

Answer 26

in book

Question 27

What is the pH range for phenolphthalein and what titrations is it suitable for?

Answer 27

8.3 to 10.0 Strong - Strong Weak - Strong

Question 28

What is the pH range for methyl orange and what titrations is it suitable for?

Answer 28

3.1 - 4.4 Strong - Strong Strong - Weak

Question 29

What is the pH range for methyl red and what titrations is it suitable for?

Answer 29

4.4 - 6.2 Strong - Strong Strong - Weak

Question 30

What is salt hydrolysis?

Answer 30

When all or some of the H+ ions in an acid are replaced with positive ions

Question 31

What are the four things that salts can be made from and what is the solution (acidic or alkaline)

Answer 31

1. Strong acid - Strong base e.g. NaCl and solution is neutral 2. Strong acid - Weak base e.g. NH4NO3, solution is acidic 3. Weak acid - Strong base e.g. CH3COONa, solution is alkaline 4. Weak acid - Weak base e.g. CH3COONH4, either acidic or alkaline

Question 32

For the previous question, for 1, 2 and 3 what happens in water.

Answer 32

1. Neither of the ions from the salt react with water 2. The positive ion react with water donating a H+ to form the acidic hydronium ion 3. The negative ion reacts with water, the water donates a H+ leaving OH- ions in solution