Chemical Changes

Question 1

What is an acid?

Answer 1

A substance that releases H⁺ (hydrogen) ions in solution

Question 2

What is an alkali?

Answer 2

A soluble base that releases OH⁻ (hydroxide) ions in solution.

Question 3

What is the pH scale?

Answer 3

A scale from 0 to 14 that measures the acidity or alkalinity of a solution.

Question 4

What pH values do acids, neutral substances, and alkalis have?

Answer 4

Acids: pH < 7, Neutral: pH 7, Alkalis: pH > 7.

Question 5

What is a neutralisation reaction?

Answer 5

Acid + Base → Salt + Water.

Question 6

What is the equation for neutralisation in terms of ions?

Answer 6

H⁺ + OH⁻ → H₂O.

Question 7

How can you measure pH?

Answer 7

Using universal indicator or a pH probe.

Question 8

What is the reaction between an acid and a metal?

Answer 8

Acid + Metal → Salt + Hydrogen.

Question 9

How can you test for hydrogen gas?

Answer 9

The squeaky pop test – a lit splint will make a “pop” sound.

Question 10

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

Answer 10

Acid + Metal Carbonate → Salt + Water + Carbon Dioxide.

Question 11

How can you test for carbon dioxide?

Answer 11

Bubble it through limewater – it turns cloudy.

Question 12

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

Answer 12

Acid + Metal Oxide → Salt + Water.

Question 13

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

Answer 13

Acid + Metal Hydroxide → Salt + Water (neutralisation).

Question 14

What is the difference between a strong acid and a weak acid?

Answer 14

Strong acids (e.g., HCl, H₂SO₄) completely ionise in water, while weak acids (e.g., ethanoic acid) only partially ionise.

Question 15

What happens to pH when acid concentration increases?

Answer 15

The pH decreases (becomes more acidic).

Question 16

What happens to pH when the acid is diluted?

Answer 16

The pH increases (becomes less acidic)

Question 17

What is the reactivity series?

Answer 17

A list of metals in order of reactivity.

Question 18

Name the top three most reactive metals in the reactivity series.

Answer 18

Potassium (K), Sodium (Na), Calcium (Ca).

Question 19

Which metals react with cold water?

Answer 19

Potassium, Sodium, Calcium (they produce hydrogen gas).

Question 20

What is displacement?

Answer 20

A more reactive metal displaces a less reactive metal from its compound.

Question 21

What happens when magnesium is placed in copper sulfate?

Answer 21

Magnesium + Copper Sulfate → Magnesium Sulfate + Copper (magnesium displaces copper).

Question 22

What is electrolysis?

Answer 22

The process of breaking down a compound using electricity.

Question 23

What happens at the cathode (-ve electrode)?

Answer 23

Positive ions (cations) gain electrons (reduction).

Question 24

What happens at the anode (+ve electrode)?

Answer 24

Negative ions (anions) lose electrons (oxidation).

Question 25

What is produced at the cathode during electrolysis of a solution?

Answer 25

Hydrogen (if the metal is more reactive than hydrogen), otherwise the metal.

Question 26

What is produced at the anode during electrolysis of a solution?

Answer 26

Oxygen (unless a halide ion is present, in which case the halogen is released).

Question 27

Who created the modern periodic table?

Answer 27

Dmitri Mendeleev in 1869.

Question 28

How did Mendeleev arrange the elements?

Answer 28

By atomic mass, but he also grouped elements with similar properties and left gaps.

Question 29

How is the modern periodic table arranged?

Answer 29

By atomic number (proton number).

Question 30

What are groups in the periodic table?

Answer 30

Vertical columns that show the number of outer shell electrons.

Question 31

What are periods in the periodic table?

Answer 31

Horizontal rows that show the number of electron shells.

Question 32

What are the properties of alkali metals?

Answer 32

Soft, low density, highly reactive, low melting points.

Question 33

How does reactivity change down Group 1?

Answer 33

Increases because the outer electron is further from the nucleus and more easily lost.

Question 34

What happens when alkali metals react with water?

Answer 34

They form a metal hydroxide + hydrogen gas.

Question 35

Why are alkali metals stored in oil?

Answer 35

To prevent reaction with oxygen and moisture in the air.

Question 36

What are the properties of halogens?

Answer 36

Non-metals, diatomic molecules, reactive.

Question 37

How does reactivity change down Group 7?

Answer 37

Decreases because the outer shell is further from the nucleus, making it harder to gain an electron.

Question 38

What is a halogen displacement reaction?

Answer 38

A more reactive halogen displaces a less reactive halogen from its compound.

Question 39

Give an example of a halogen displacement reaction.

Answer 39

Chlorine + Potassium Bromide → Potassium Chloride + Bromine.

Question 40

What are the properties of noble gases?

Answer 40

Unreactive, colorless gases, low boiling points.

Question 41

Why are noble gases unreactive?

Answer 41

They have a full outer shell of electrons.

Question 42

How does boiling point change down Group 0?

Answer 42

Increases due to stronger intermolecular forces.