Acids, Bases & Oxides

Question 1

What is an Arrhenius / ionic acid?

Answer 1

A substance when dissolved in water, ionises to produce hydrogen ions.

Question 2

What is an Arrhenius / ionic base?

Answer 2

A substance when dissolved in water, ionises to produce hydroxide ions.

Question 3

What are 2 limitations of Arrhenius / ionic theory?

Answer 3

1. since acids and bases dissolved to produce H+ or OH- ions, they must contain those ions.

–> ammonia is weak base, but it does not contain OH-. it dissolves in water to produce OH-.

NH3 + H2O ⇌ (NH4)+ + OH-

2. cannot explain acid-base reactions that do not produce water.

HCl + NH3 –> NH4Cl

Question 4

What is a Bronsted-Lowry / proton transfer theory acid?

Answer 4

A substance that is capable of donating a proton

Question 5

What is a Bronsted-Lowry / proton transfer theory base?

Answer 5

A substance that is capable of accepting a proton

Question 6

What is a limitation of BL / proton transfer theory?

Answer 6

1. cannot explain acid-base reactions that do not involve hydrogen transfer.

BF3 + NH3 —> NH3BF3

Question 7

Explain conjugate acid

Answer 7

[Bronsted-Lowry / Proton transfer theory]

Since a BL base receives a proton to form an ion, the ion can donate a proton in the reverse direction, making it a conjugate acid

Question 8

Explain conjugate base

Answer 8

[Bronsted-Lowry / Proton transfer theory]

Since a BL acid donates a proton to form an ion, the ion can accept a proton in the reverse direction, making it a conjugate base

Question 9

Amphiprotic vs Amphoteric

Answer 9

Amphiprotic = both can donate and accept a proton

Amphoteric = both acts as acid and base

Question 10

Example of amphoteric BL acid / base

Answer 10

H2O (water)

BL acid: H2O + HN3 –> NH4+ + OH-
BL base: H2O + HCl –> H3O+ + Cl-

Question 11

What is a Lewis (electron pair transfer theory) acid?

Answer 11

A substance that can receive a pair of elections

Question 12

What is a Lewis (electron pair transfer theory) base?

Answer 12

A substance that can donate a pair of elections

Question 13

Limitation of Lewis theory

Answer 13

1. Since there is the donation of an electron pair, dative bonding must happen. However, this is not always true. It cannot explain acid-base reactions that do not involve dative (coordinate) bonding.

(common acids & bases don’t have dative bonding)

HCl + NaOH –> NaCl + H2O

Question 14

Are lewis bases = BL bases?

Answer 14

Yes

Question 15

Are lewis acids = BL acids?

Answer 15

No.

BL acid is a subset of Lewis acid. Because BL acids need to have H+ present, which is not necessary in lewis acid.

Lewis acids that are deficient of electrons are not BL acids. Lewis acids that do not have hydrogen are not BL acids.

Eg: BF3 (boron trifluoride), AlCl3 (aluminium chloride)

B and Al only have 6 valence e-

Question 16

Characteristics of acids

Answer 16

1. Sour
2. Corrosive
3. Causes colour change in pH indicators

Question 17

Characteristics of bases

Answer 17

1. Bitter
2. Soapy
3. Corrosive
4. Causes colour change in pH indicators

Question 18

Uses of acids?

Answer 18

1. HCl: Clean steel
2. HNO3: Fertiliser
3. H2SO4: Batteries, fertiliser
4. H3PO4: Detergent, fertiliser, soft drinks

Question 19

Uses of base?

Answer 19

1. Al(OH)3: Colourfast fabric, water treatment, plant.
   (it is a sticky gel that traps impurities)
2. NaOH: Drain cleaner, soap, textiles, paper, bleach
3. NH3: Cleaners, fertilizer, make nylon
4. KOH: Batteries, fertilizer, soap, etc

Question 20

Define pH

Answer 20

The measure of concentration of free hydrogen ions or hydroxide ions in a solution

Question 21

Strong VS Weak acid

Answer 21

Strong –> completely ionized in water to form hydrogen ions

Weak –> partially ionized in water to form hydroxide ions

The concentration of hydrogen ions released by strong acids is higher, hence those acids are stronger

Question 22

What is strength of acid?

Answer 22

Degree of ionisation to produce hydrogen ions, when acid dissolves in water

Question 23

What is basicity of acid?

Answer 23

The number of moles of hydrogen ions produced when 1 mole of acid dissolves in water

Question 24

Explain what is a monobasic acid

Answer 24

A monobasic acid has 1 replaceable hydrogen atom per one acid molecule

Can only donate 1 hydrogen ion per mole of acid for an acid-base reaction

No step-wise dissociation

Question 25

Explain what is a dibasic acid

Answer 25

A dibasic acid has 2 replaceable hydrogen atoms per one acid molecule Can donate 2 hydrogen ions per mole of acid for an acid-base reaction Dissociates in 2 steps

Question 26

Explain what is a tribasic acid

Answer 26

A dibasic acid has 3 replaceable hydrogen atoms per one acid molecule Can donate 3 hydrogen ions per mole of acid for an acid-base reaction Dissociates in 3 steps

Question 27

Examples of monobasic acid

Answer 27

1. HCl (hydrochloric) 2. HNO3 (nitric) 3. CH3COOH (ethanoic)

Question 28

Examples of dibasic acid

Answer 28

1. H2SO4 (sulfuric) 2. H2CO3 (carbonic)

Question 29

Examples of tribasic acid

Answer 29

1. H3PO4 (phosphoric)

Question 30

List the strong acids

Answer 30

1. HCl 2. HNO3 3. H2SO4

Question 31

List the weak acids

Answer 31

1. H3PO4 2. H2CO3 3. CH3COOH

Question 32

Acid + metal -->

Answer 32

Salt + H2

Question 33

Acid + base (metal oxide / hydroxide) -->

Answer 33

Salt + H2O

Question 34

Acid + metal carbonate -->

Answer 34

Salt + H2O + CO2

Question 35

Ammonium salt + Alkali (metal oxide / hydroxide)

Answer 35

Salt + Ammonia (g) + H2O

Question 36

Metal + water -->

Answer 36

Salt + H2 (v reactive metal: hydroxide, mildly reactive metal: oxide)

Question 37

Bonding & structure of acid

Answer 37

Covalent bonding, simple molecular structure *but they become ions when dissolved in water

Question 38

Bonding & structure of base

Answer 38

Ionic bonding, giant ionic lattice structure *except for NH3 (aq) which has both covalent & ionic bonds when dissolved in water NH4+ and OH- NH4+ has dative covalent bonds

Question 39

What is strength of alkali

Answer 39

Degree of ionisation to produce hydroxide ions, when alkalis dissolve in water

Question 40

What is a strong alkali

Answer 40

A substance that completely ionises in water to produce hydroxide ions

Question 41

What is a weak alkali

Answer 41

A substance that partially ionises in water to produce hydroxide ions

Question 42

List the strong alkalis

Answer 42

NaOH (sodium hydroxide, Lye) KOH Ca(OH)2 (limewater)

Question 43

List a weak alkali

Answer 43

NH3, Ammonia

Question 44

Basicity of alkalis

Answer 44

The number of moles of hydroxide ions produced when 1 mole of alkali dissolves in water

Question 45

What is a monobasic alkali

Answer 45

An alkali that has 1 replaceable hydroxide ion per alkali molecule

Question 46

Examples of monobasic alkali

Answer 46

1. NaOH 2. KOH 3. NH3

Question 47

Examples of dibasic alkali

Answer 47

1. Ca(OH)2

Question 48

What are acidic oxides?

Answer 48

Non-metal oxides that act as acids

Question 49

Examples of acidic oxides?

Answer 49

1. CO2 2. NO2 3. SO2 4. SO3 5. P4O10 (phosphorus pentoxide)

Question 50

What are neutral oxides?

Answer 50

Non-metal oxides that don't react with both acid and alkali

Question 51

Examples of neutral oxides?

Answer 51

1. CO 2. NO (nitric oxide) 3. N2O (nitrous oxide) 4. H2O 5. H2O2

Question 52

What are basic oxides?

Answer 52

Metal oxides that act as a base

Question 53

Examples of basic oxides?

Answer 53

1. MgO 2. Na2O 3. CaO

Question 54

What are amphoteric oxides?

Answer 54

Metal oxides that can act as both a base and alkali, hence react with both alkalis and bases

Question 55

Examples of amphoteric oxides?

Answer 55

1. Al2O3 2. PbO 3. ZnO

Question 56

Colour change of phenolphthalein

Answer 56

under pH9: colourless above pH9: pink