Acids

Question 1

Give the definition of an acid

Answer 1

Acid – A compound that dissolves in water to produce hydrogen ions (H+)

Question 2

Give the definition of a base

Answer 2

Base – A substance that reacts with acid producing a salt and water.

Question 3

Give the definition of an alkali

Answer 3

Alkali – Soluble bases which dissolve in water to produce hydroxide ions OH-

Question 4

Give the definition of neutralisation

Answer 4

Neutralisation - H+ (aq) + OH-(aq) -> H2O(l)

Question 5

Give the definition of monoprotic

Answer 5

Monoprotic – 1 mole of acid produces 1 mole of H+ ions.

Question 6

Give the definition of diprotic

Answer 6

Diprotic – 1 mole of acid produces 2 moles of H+ ions.

Question 7

Give the definition of a Hydonium ion or hydroxonium ion or oxonium ion.

Answer 7

Hydonium ion or hydroxonium ion or oxonium ion – H3O+. It is the ion formed when acids react with water.

Question 8

Give the definition of a buffer

Answer 8

Buffer – solutions that can resist changes in pH when small quantities of acid or base are added.

Question 9

Give the definition of a Bronsted-Lowry acid

Answer 9

A Bronsted-Lowry acid is a proton donor.

Question 10

Give the definition of a Bronsted-Lowry base

Answer 10

A Bronsted-Lowry base is a proton acceptor.

Question 11

What happens to strong bases in aqueous solution?

Answer 11

Strong acids (HCl, H2SO4, HNO3) and bases (NaOH, KOH) completely dissociate in aqueous solution.

Question 12

What happens to weak bases in aqueous solution?

Answer 12

Weak acids and bases are slightly dissociated in aqueous solution.

Question 13

How do you calculate the new concentration of a solution?

Answer 13

New concentration of a solution = amount in moles of

Question 14

What is the equation for pH?

Answer 14

pH = -log10[H+]

Question 15

What is the equation for [H+]?

Answer 15

[H+] = 10(-pH)

Question 16

What is the equation for Kw?

Answer 16

Kw=[H+] [OH-] units mol2dm-6

Question 17

At 25oC what does Kw equal?

Answer 17

At 25oC Kw = 1.00 x 10-14

Question 18

In pure water how would you calculate [H+]?

Answer 18

In pure water [H+] = √Kw

Question 19

What is the equation for pKw?

Answer 19

pKw = -log10Kw (14 at 25oC)

Question 20

What is the equation for pOH?

Answer 20

pOH = log10 [OH-]

Question 21

What is the link between pOH and pH?

Answer 21

pOH + pH = pKw

Question 22

Give the equilibrium equation for the dissociation of HA.

Answer 22

HA H+ + A-

Question 23

What is the equation for Ka?

Answer 23

Ka = [A-] [H+] /[HA]

Question 24

What is the equation for pKa?

Answer 24

pKa = -log10[Ka]

Question 25

How do you work out the concentration of a weak acid?

Answer 25

[Weak acid]=[H+]2 / Ka

Question 26

What is an acidic buffer formed from?

Answer 26

Formed from weak acid and its salt

Question 27

What happens when you add acid to an acidic buffer solution?

Answer 27

When small amount of acid is added extra H+ ions are added.

Question 28

What happens to the position of equilibrium of an acidic buffer solution?

Answer 28

The position of equilibria moves to the LEFT to remove the H+ ions.

Question 29

What happens to the pH of an acidic buffer solution?

Answer 29

This keeps the pH almost constant.

Question 30

What happens to a buffer when a base is added?

Answer 30

When a small amount of base is added extra hydroxide OH- ions are added.

Question 31

How are the hydroxide ions removed?

Answer 31

The hydroxide ions react with the hydrogen ions removing some of the H+ ions.

Question 32

What happens to the position of equilibrium if bases are added and why?

Answer 32

The position of equilibrium moves to the RIGHT to replace the H+ ions.

Question 33

What happens to the pH of a buffer when bases are added?

Answer 33

This keeps the pH almost constant.

Question 34

What is an acidic buffer formed from?

Answer 34

Basic buffers

Question 35

Give the equation for the dissociation of a basic buffer.  

Answer 35

B + H+     BH+

Question 36

What happens when you add acid to a basic buffer solution?

Answer 36

When small amount of acid is added extra H+ ions are removed as they react with the base B.

Question 37

What happens to the position of equilibrium of a basic buffer solution?

Answer 37

The position of equilibrium moves to the RIGHT.

Question 38

What happens to a basic buffer when a base is added?

Answer 38

When a small amount of base is added extra hydroxide OH- ions are added.

Question 39

How are the hydroxide ions removed?

Answer 39

The hydroxide ions react with the hydrogen ions in the buffer removing some of the H+ ions.

Question 40

What happens to the position of equilibrium if bases are added to a basic buffer and why?

Answer 40

The position of equilibrium moves to the LEFT to replace the H+ ions

Question 41

What pH range does Thymol blue work over and what is the colour change in acid and in alkali?

Answer 41

Thymol blue 1.20-2.80 red – yellow (acid – alkali)

Question 42

What pH range does Methyl orange work over and what is the colour change in acid and in alkali?

Answer 42

Methyl orange 3.10-4.40 red – yellow

Question 43

What pH range does Methyl red work over and what is the colour change in acid and in alkali?

Answer 43

Methyl red 4.40-6.20 red – yellow

Question 44

What pH range does Bromothymol blue work over and what is the colour change in acid and in alkali?

Answer 44

Bromothymol blue 6.00-7.60 yellow – blue

Question 45

What pH range does Phenolphthalein work over and what is the colour change in acid and in alkali?

Answer 45

Phenolphthalein 8.30-10.00 colourless – pink.