4.4 Chemical changes

Question 1

What is an acid?

Answer 1

An acid is a substance that releases hydrogen ions (H⁺) in solution.

Question 2

What is an alkali?

Answer 2

An alkali is a substance that releases hydroxide ions (OH⁻) in solution.

Question 3

What is the pH scale?

Answer 3

The pH scale measures the acidity or alkalinity of a solution, ranging from 0 (acidic) to 14 (alkaline), with 7 being neutral.

Question 4

What pH value do acids have?

Answer 4

Acids have a pH value less than 7.

Question 5

What pH value do alkalis have?

Answer 5

Alkalis have a pH value greater than 7.

Question 6

What pH value is considered neutral?

Answer 6

A pH value of 7 is considered neutral (e.g., pure water).

Question 7

What is a neutralization reaction?

Answer 7

A neutralization reaction occurs when an acid reacts with a base (alkali), producing water and a salt.

Question 8

What is the general equation for a neutralization reaction?

Answer 8

Acid + Base → Salt + Water.

Question 9

What is the formula for hydrochloric acid?

Answer 9

HCl.

Question 10

What is the formula for sulfuric acid?

Answer 10

H₂SO₄.

Question 11

What is the formula for nitric acid?

Answer 11

HNO₃.

Question 12

What is the formula for sodium hydroxide (a common alkali)?

Answer 12

NaOH.

Question 13

What is an indicator?

Answer 13

An indicator is a substance that changes color to show whether a solution is acidic, neutral, or alkaline.

Question 14

What is litmus paper?

Answer 14

Litmus paper is a type of indicator that turns red in acidic solutions and blue in alkaline solutions.

Question 15

What is universal indicator?

Answer 15

Universal indicator is a mixture of indicators that shows a range of colors to indicate pH from red (strong acid) to purple (strong alkali).

Question 16

What is an example of a strong acid?

Answer 16

HCl (hydrochloric acid).

Question 17

What is an example of a weak acid?

Answer 17

Acetic acid (CH₃COOH) found in vinegar.

Question 18

What is an example of a strong alkali?

Answer 18

Sodium hydroxide (NaOH).

Question 19

What is an example of a weak alkali?

Answer 19

Ammonia solution (NH₃).

Question 20

What is a base?

Answer 20

A base is a substance that can accept hydrogen ions (H⁺).

Question 21

What is the reaction between an acid and a metal?

Answer 21

Acid + Metal → Salt + Hydrogen gas.

Question 22

What is the reaction between an acid and a metal carbonate?

Answer 22

Acid + Metal carbonate → Salt + Water + Carbon dioxide.

Question 23

What happens during the electrolysis of water?

Answer 23

Electrolysis of water splits water (H₂O) into hydrogen gas (H₂) and oxygen gas (O₂) using an electric current.

Question 24

What is electrolysis?

Answer 24

Electrolysis is a process in which electrical energy is used to cause a non-spontaneous chemical reaction.

Question 25

What is the anode?

Answer 25

The anode is the positive electrode where oxidation occurs during electrolysis.

Question 26

What is the cathode?

Answer 26

The cathode is the negative electrode where reduction occurs during electrolysis.

Question 27

What happens at the cathode during electrolysis?

Answer 27

At the cathode, positive ions gain electrons (reduction) and form solid products.

Question 28

What happens at the anode during electrolysis?

Answer 28

At the anode, negative ions lose electrons (oxidation) and form gas products.

Question 29

What is an example of a product formed at the cathode during electrolysis of aqueous solutions?

Answer 29

Hydrogen gas (H₂) can be formed at the cathode.

Question 30

What is an example of a product formed at the anode during electrolysis of aqueous solutions?

Answer 30

Oxygen gas (O₂) can be formed at the anode.

Question 31

What is oxidation?

Answer 31

Oxidation is the loss of electrons.

Question 32

What is reduction?

Answer 32

Reduction is the gain of electrons.

Question 33

What is the reactivity series?

Answer 33

The reactivity series is a list of metals ranked from the most reactive to the least reactive.

Question 34

What is a displacement reaction?

Answer 34

A displacement reaction occurs when a more reactive element displaces a less reactive element from a compound.

Question 35

What is an example of a displacement reaction?

Answer 35

When zinc reacts with copper sulfate (CuSO₄) to form zinc sulfate (ZnSO₄) and copper metal (Cu).

Question 36

What happens during the reaction between a metal and an acid?

Answer 36

The metal reacts with the acid to produce hydrogen gas and a salt.

Question 37

What are the products of the reaction between sodium and water?

Answer 37

The products are sodium hydroxide (NaOH) and hydrogen gas (H₂).

Question 38

What are the products of the reaction between potassium and water?

Answer 38

The products are potassium hydroxide (KOH) and hydrogen gas (H₂).

Question 39

What is a redox reaction?

Answer 39

A redox reaction is a reaction in which both reduction and oxidation occur simultaneously.

Question 40

What is the oxidation number of hydrogen in most compounds?

Answer 40

1

Question 41

What is the oxidation number of oxygen in most compounds?

Answer 41

-2

Question 42

What happens during the reaction of acids with bases?

Answer 42

Acids neutralize bases to form water and salts.

Question 43

What is an example of a salt produced from an acid-base reaction?

Answer 43

When hydrochloric acid reacts with sodium hydroxide, sodium chloride (NaCl) and water are produced.

Question 44

What is an example of a salt produced from an acid and a metal?

Answer 44

When hydrochloric acid reacts with zinc, zinc chloride (ZnCl₂) and hydrogen gas are produced.

Question 45

What is a salt?

Answer 45

A salt is a compound formed from the reaction of an acid with a base or metal.

Question 46

What is the main use of sulfuric acid in industry?

Answer 46

Sulfuric acid is used in the manufacture of fertilizers, detergents, and in oil refining.

Question 47

What is the main use of hydrochloric acid in industry?

Answer 47

Hydrochloric acid is used in metal cleaning and in the production of PVC (polyvinyl chloride).