Chap.11: Chemical Changes

Question 1

What is a physical change?

Answer 1

A change in which no new substance is formed

Question 2

Ways to tell if there is a chemical change

Answer 2

1. Change in colour
2. Change in temperature
3. Production of gas
4. Production of solid

Question 3

What are the different chemical changes

Answer 3

1. Combustion
2. Thermal decomposition (TD)
3. Oxidation
4. Neutralisation

Question 4

Describe combustion

Answer 4

Substance is heated in presence of oxygen
Heat and light usually formed

Question 5

Describe TD

Answer 5

Substance breaks down breaks down into two or more simpler substances in heat

Question 6

Define acid

Answer 6

An acid is a substance that dissolves and dissociates in water to produce hydrogen ions (Hplus ion) and the corresponding negative ion

Question 7

Define base

Answer 7

A base is a substance that reacts with an acid to produce salt and water only. Bases are usually metal oxides or hydroxides

Question 8

Define alkali

Answer 8

Akali is a base that dissolves and dissociates in water to produce hydroxide (OH-)ions and the corresponding positive ion

Question 9

How to determine the acidity/akalinity of a solution?

Answer 9

1. Use of pH scale- 0 (Acidic)–14 (akaline)
2. Litmus paper (blue to red=Acidic)
3. Universal indicator- provides approximate pH values
4. pH meter- Obtains most accurate value

Question 10

What are the different reactions of acids?

Answer 10

1. Acid with akali
2. Acid with metals
3. Acid with carbonates

Question 11

What happens during an acid and akali reaction?

Answer 11

• Neutralisation reaction
• Produces salt and water

Question 12

What happens during an acid and metal reaction?

Answer 12

• Acids can react with a reactive metal to form salt and hydrogen gas (Cu,Ag,Au are non reactive)
• Use of lighted splint test (for hydrogen gas)

Question 13

What happens during an acid and carbonate reaction?

Answer 13

• Forms salt, CO2 and water
• Use of limewater test (for carbon dioxide gas)

Question 14

What are the two formulas for compounds?

Answer 14

1. Ionic (Metal+non-metal)
2. Covalent (non-metal+non_metal)

Question 15

Covalent compounds special characteristic is?

Answer 15

It usually has a prefix to indicate the number of atoms present in the molecule (eg. mono, di, tri, tetra, pentra, hexa)

Question 16

Where are cations/anion with charge 3+/3- and below found?

Answer 16

Cations: Groups 1(+), 2(2+), 3(3+)
Anions: Grps 15 (3-), 16 (2-), 17 (-)

Question 17

How to get charges of transition metals?

Answer 17

Roman numerals on name indicate charge. It will be an cation as it is a metal (+)

Question 18

Polyatomic ions (MEMORISE)

Answer 18

• Ammonium-> NH4 +
• Hydroxide-> OH -
• Nitrate-> NO3 -
• Sulfate-> SO4 2-
• Carbonate-> CO3 2-

Question 19

What is the law and conservation of mass

Answer 19

During a chemical reaction, atoms are neither created or destroyed

Therefore, total number of atoms and after the chemical reaction is balanced (same number or products and reactants)

Question 20

Chemical formula of Hydrogen

Answer 20

H+

Question 21

Chemical formula of sliver ion

Answer 21

Ag +

Question 22

Chemical formula of Zinc ion

Answer 22

Zn 2+

Question 23

Chemical formula of Ammonium ion

Answer 23

NH4 +

Question 24

Chemical formula of Hydride ion

Answer 24

H -

Question 25

Chemical formula of Hydroxide ion

Answer 25

OH -

Question 26

Chemical formula of Nitrate

Answer 26

NO3 -

Question 27

Chemical formula of Carbonate ion

Answer 27

CO3 2-

Question 28

Chemical formula of sulfate ion

Answer 28

SO4 2-

Question 29

What are the prefixes or covalent molecules

Answer 29

Number of atoms-
1- Mono
2- Di
3- Tri
4- Tetra
5- Pentra
6- Hexa

Question 30

Chemical formula of Nitric acid

Answer 30

HNO3

Question 31

Chemical formula of Hydrochloric acid

Answer 31

HCl

Question 32

Chemical formula of sulfuric acid

Answer 32

H2SO4

Question 33

Chemical formula of ammonia

Answer 33

NH3