Elements and Substances

Question 1

1. Hydrogen

Answer 1

The first element, capable of forming cations and anions, flammable and explosive

Question 2

1.2 Reactions producing hydrogen

Answer 2

1. Reaction between alkali metal / alkaline earth metal and water
2. Electrolysis of water
3. Steam reforming of methane

Question 3

1.3 Reactions consuming hydrogen

Answer 3

1. Catalytic hydrogenation of alkenes
2. Haber process

Question 4

2. Helium

Answer 4

Lightest noble gas, only noble gas without octet structure in the outermost electron shell

Question 5

3. Lithium

Answer 5

First alkali metal, reacts vigorously with water

Question 6

3.2 Lithium ion batteries

Answer 6

Positive electrode: lithium cobalt oxide; negative electrode: lithium atoms lying between graphite sheets; electrolyte: lithium salt dissolved in organic solvent
Used on portable electronic devices
Do not bring close to water

Question 7

3.3 Reactions involving lithium compounds

Answer 7

Lithium aluminium hydride in dry ether followed by acid, reduction of carboxylic acid, aldehydes, and ketones but NOT alkenes

Question 8

5. Boron

Answer 8

Giant covalent structure, metalloid

Question 9

5.2 Boron compounds

Answer 9

Boron trifluoride, trigonal planar shape, non-polar

Question 10

6. Carbon

Answer 10

Many allotropes, can form many organic compounds, graphite can conduct electricity.

Question 11

6.2 Graphite

Answer 11

Hexagonal layered giant covalent structure, has delocalised electrons which can conduct electricity, hence used to make electrodes and other conducting material.
High melting and boiling point, insoluble in any solvent.

Question 12

6.3 Diamond

Answer 12

Giant covalent structure, tetrahedral structure, cannot conduct electricity.
Very hard, high melting and boiling point, insoluble in any solvent.
Used to make abrasives to grind glass or stone.

Question 13

6.4 Carbon dioxide molecular properties

Answer 13

Two double covalent bonds, linear shape, non-polar

Question 14

6.5 Reactions producing carbon dioxide

Answer 14

1. Reaction between metal carbonate and acid (endothermic)
2. Complete combustion of hydrocarbons (exothermic)
3. Conversion from carbon monoxide to carbon dioxide in catalytic converter / carbon (monoxide) reduction in metal extraction (exothermic)
4. Respiration (exothermic)

Question 15

6.6 Reactions consuming carbon dioxide

Answer 15

1. Formation of carbonic acid with carbon dioxide and water
2. Reaction of sodium hydroxide with carbon dioxide
3. Reaction of carbon dioxide with limewater (calcium hydroxide) producing calcium carbonate
4. Reaction of milky limewater (calcium carbonate), carbon dioxide, and water, producing calcium hydrogencarbonate
5. Photosynthesis

Question 16

7. Nitrogen

Answer 16

Triple covalent bond, stable in room temperature but forms nitrogen oxides in air at high temperatures

Question 17

7.2 Reactions involving nitrogen

Answer 17

Haber process (fine iron powder catalyst)
N₂ + 3H₂ -> 2NH₃

Question 18

7.3 Reactions involving nitrogen oxides

Answer 18

1. Production of nitrogen oxides in high-temperature combustion engines
2. Conversion of nitrogen oxides into nitrogen gas in catalytic converter

Question 19

7.4 Reactions producing nitrogen monoxide

Answer 19

Reduction of dilute nitric acid: NO₃^- + 4H⁺ + 3e^- -> NO + 2H₂O

Question 20

7.5 Reactions producing nitrogen dioxide

Answer 20

Reduction of concentrated nitric acid: NO₃^- + 2H⁺ + e^- -> NO₂ + H₂O

Question 21

7a1. Ammonia gas

Answer 21

Produced in Haber process, form ammonium ions in water
Turns moist red litmus paper from red to blue and moist pH paper to purple
Pungent smell
Trigonal pyramidal shape, polar, soluble in water

Question 22

7a2. Ammonium ion

Answer 22

Only in-syllabus non-metal positive ion, compounds are always soluble in water
Dative covalent bond

Question 23

7a3. Ammonia metal ion solubilities

Answer 23

Yes: zinc, copper, calcium, silver ions
No: iron, magnesium, aluminium, lead ions
Colour changes: copper: pale blue to prussian blue; silver: white to grey; iron: reddish brown (3+) / dirty green (2+) precipitate formed

Question 24

7a4. Ammonia gas collection method

Answer 24

Upward delivery into an inverted flask since ammonia gas is less dense than air.
X water displacement since ammonia is highly soluble in water.

Question 25

7a5. Reactions consuming ammonia

Answer 25

1. Formation of unsubstituted amides with carboxylic acids and ammonia

Question 26

7a6. Reactions producing ammonia

Answer 26

1. Reaction of sodium hydroxide with ammonium compounds, producing ammonia gas and the sodium salt eg. NH₄NO₃ + NaOH -> NH₃ + NaNO₃ + H₂O 2. Alkaline hydrolysis of unsubstituted amides (X acid hydrolysis)

Question 27

7b1. Nitric acid

Answer 27

Corrosive, stored in brown bottle, both dilute and concentrated forms serve as oxidising agents.

Question 28

7b2. Nitrate ion

Answer 28

NO₃^- 1. Compounds always soluble in water, used to make salt bridges 2. Very very weak reducing agent which is never discharged in electrolysis 3. Nitrate ion with hydrogen ion (nitric acid) is a strong oxidising agent at different concentrations 4. Used to form silver nitrate, which is used in chloride test

Question 29

7b3. Nitrite ion

Answer 29

NO₂^-

Question 30

8.1 Oxygen

Answer 30

Oxidising agent, not flammable Double covalent bond

Question 31

8.2 Reactions producing oxygen

Answer 31

1. Electrolysis of water / other dilute solutions 2. Oxidation of metals 3. Producing oxides of non-metals by heating in air (silicon, phosphorus, sulphur) 2. Photosynthesis