C11 | 화학적 변화 (Chemical Changes)

Question 1

What are the two types of changes?

Answer 1

• Chemical Change
• Physical Change

Question 2

What is the definition of a Physical Change?

Answer 2

A change in which no new substance is formed.

Question 3

What is the definition of Chemical Change?

Answer 3

A change in which a new substance is formed.

Question 4

How easy is it to reverse the process of Physical Changes?

Answer 4

Easy, we can get the substituents back using separation techniques.

Question 5

How easy is it to reverse the process of Chemical Changes?

Answer 5

Difficult, we cannot get back the reactants easily.

Question 6

What are some examples of Physical Changes?

Answer 6

• Change of State
  (Boiling of Water)
• Expansion & Contraction

Question 7

What are some examples of Chemical Changes?

Answer 7

• Rusting
• Burning

Question 8

What are the four types of Chemical Changes?

Answer 8

• Combustion
• Thermal Decomposition
• Oxidation
• Neutralisation

Question 9

What is combustion?

Answer 9

• Combustion is a chemical reaction in which a substance is heated in the presence of oxygen to form one or more new substances. Heat and light are usually given out during combustion.
• Examples include the following chemical equations:
• Carbon + Oxygen → Carbon Dioxide (In the presence of heat)
• Sulfur + Oxygen → Sulfur Dioxide (In the presence of heat)

Question 10

What is Thermal Decomposition?

Answer 10

• Thermal decomposition is a process in which a substance is broken down into two or more simpler substances upon heating.
  Example:
  1. Sugar → Carbon + Water Vapour (In the presence of heat)
  2. Calcium Carbonate → Calcium Oxide + Carbon Dioxide (In the presence of heat)

Question 11

What is Oxidation - Rusting?

Answer 11

Matter is able to interact with oxygen. When a substance gains oxygen, it undergoes a chemical change called oxidation.

Question 12

Oxidation - Cellular Respiration

What is Cellular Respiration?

Answer 12

• Cellular Respiration is an oxidation reaction that occurs in the cells of living things.
• Matter is able to interact with oxygen. When a substance gains oxygen, it undergoes a chemical change called oxidation.
  Example:
  Glucose + Oxygen → Carbon Dioxide + Water

Question 13

What is Neutralisation?

Answer 13

When an acid mixes with an alkali, a neutralisation occurs.

Question 14

Characteristics of Acids

Hint: Taste, Effect on Objects, Litmus Paper, Reaction

Answer 14

• Sour Taste
• Corrosive (Some)
• Turns Blue Litmus Paper Red
• Reacts with Alkali, Metals and Carbonates

Question 15

Characteristics of Alkali

Hint: Taste, Effect on Objects, Litmus Paper, Reaction

Answer 15

• Bitter Taste
• Soapy Feel
• Corrosive (Some)
• Turns Red Litmus Paper Blue
• Reacts with acid in neutralisation reactions.
  Examples:
  Baking Soda, Sodium Hydroxide, Ammonia, Potassium Hydroxide, Calcium Hydroxide

Question 16

Word Equation for Neutralisation

Answer 16

Alkali + Acid → Salt + Water
* Toothpaste contains alkali, which neutralises the acid formed in our teeth by bacteria.
Example:
Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water
* The word “salt” is a general term for a compound containing an element that is a metal. E.g. salts containing the element
potassium include potassium chloride, potassium sulfate and potassium nitrate etc.

Question 17

Word Equation for Acid & Metal Reaction

Answer 17

Acid + Metal → Salt + Hydrogen Gas
Example:
Hydrochloric Acid + Magnesium → Magnesium Chloride + Hydrogen Gas
* However, not all metals react with an acid in the same manner. Some metals (e.g. copper, silver, gold) do not react with acids.

Question 18

What is the test and observation for Hydrogen Gas?

Answer 18

Test: Insert a lighted splint.
Observation: Colourless gas produced extinguishes a lighted splint with a ‘pop’ sound.

Question 19

Word Equation for Acid & Carbonate Reaction

Answer 19

Acid + Carbonate → Salt + Carbon Dioxide Gas + Water
Examples:
Hydrochloric Acid + Calcium Carbonate → Calcium Chloride + Carbon Dioxide Gas + Water

Question 20

What is the test and observation for Carbon Dioxide?

Answer 20

Test: Bubble the gas into limewater.
Observation: When the gas produced is bubbled into limewater, a white precipitate is formed on limewater.

Question 21

What is the pH range for Acid, Alkali and Neutral?

Answer 21

• Solutions pH < 7 are acidic.
• Solutions pH> 7 are alkalinic.
• Solutions pH = 7 are neutral.
• The lower the pH value, the more acidic the solution.
• The higher the pH value, the alkaline the solution.

Question 22

What is an Indicator?

Answer 22

An indicator is a substance which changes colour depending on whether the solution being tested is acidic or alkalinic.

Question 23

Litmus Paper
In acids, what colour does the Red & Blue Litmus Paper turn into?
In alkali, what colour does the Red & Blue Litmus Paper turn into?
In Neutral Solution, what colour does the Red & Blue Litmus Paper turn into?

Answer 23

In acids, blue litmus paper turns red, and the red litmus paper remains red.
In alkali, blue litmus paper stays blue, and the red litmus paper turns blue.
In neutral solution, blue litmus paper stays blue, and the red litmus paper stays red.

Question 24

What is Electrolysis?

Answer 24

Electrolysis is the chemical decomposition of substances with the passage of an electric current.
Example:
Water → (with electricity) Hydrogen + Oxygen

Question 25

What is Electroplating?

Answer 25

Electroplating is the process in which a substance is coated with a metal with the passage of an electric current.