1. Principles of Chemistry

Question 1

What are the three states of matter?

Answer 1

Solid, liquid, and gas.

Question 2

How are particles arranged in a solid?

Answer 2

Particles are tightly packed in a regular arrangement, vibrating in fixed positions.

Question 3

How are particles arranged in a liquid?

Answer 3

Particles are close together but can move past each other, with a less regular arrangement.

Question 4

How are particles arranged in a gas?

Answer 4

Particles are far apart, moving randomly with high energy and no fixed arrangement.

Question 5

What are the interconversions between states of matter?

Answer 5

Melting, freezing, boiling, condensing, sublimation, and deposition.

Question 6

How is melting achieved?

Answer 6

By heating a solid to its melting point, increasing particle energy.

Question 7

How is condensation achieved?

Answer 7

By cooling a gas below its boiling point, decreasing particle energy.

Question 8

What experiment explains diffusion of gases?

Answer 8

Gases diffuse from high to low concentration, observed by spreading of perfume in air.

Question 9

What is a solvent?

Answer 9

The substance in which a solute dissolves.

Question 10

What is a solute?

Answer 10

The substance dissolved in a solvent.

Question 11

What is a solution?

Answer 11

A homogeneous mixture of solute and solvent.

Question 12

What is a saturated solution?

Answer 12

A solution that contains the maximum amount of solute dissolved at a given temperature.

Question 13

How do you classify a substance as an element, compound, or mixture?

Answer 13

Element: made of one type of atom; compound: made of two or more elements chemically bonded; mixture: physically combined substances.

Question 14

Do pure substances have fixed melting and boiling points?

Answer 14

Yes. Mixtures melt or boil over a range of temperatures.

Question 15

Name techniques to separate mixtures.

Answer 15

• Simple distillation
• Fractional distillation
• Filtration
• Crystallisation
• Paper chromatography

Question 16

How does a chromatogram show the composition of a mixture?

Answer 16

By displaying different spots or bands representing components; Rf values help identify them.

Question 17

How do you calculate Rf values?

Answer 17

Rf = distance moved by substance / distance moved by solvent front.

Question 18

What is an atom?

Answer 18

The smallest unit of an element, consisting of protons, neutrons, and electrons.

Question 19

What is a molecule?

Answer 19

Two or more atoms bonded together.

Question 20

Where are sub-atomic particles located?

Answer 20

Protons and neutrons in the nucleus; electrons in shells surrounding the nucleus.

Question 21

What are atomic number and mass number?

Answer 21

• Atomic number: number of protons
• Mass number: protons + neutrons

Question 22

What are isotopes?

Answer 22

Atoms with the same atomic number but different neutron numbers.

Question 23

How is relative atomic mass (Ar) calculated?

Answer 23

Using isotopic abundances: Ar = (sum of isotopic mass × abundance) / 100.

Question 24

How are elements arranged in the periodic table?

Answer 24

In order of increasing atomic number, in groups (columns) and periods (rows).

Question 25

How do you deduce electronic configuration from the periodic table?

Answer 25

By the group number: main group elements have electrons in s and p shells according to their group.

Question 26

How are metals and non-metals classified?

Answer 26

Metals are to the left and middle; non-metals to the right.

Question 27

Why do elements in the same group have similar properties?

Answer 27

Because they have the same number of electrons in their outer shell.

Question 28

Why are noble gases unreactive?

Answer 28

Because their outer shells are full.

Question 29

How do you write a word and balanced symbol equation?

Answer 29

Word: describing substances; balanced: ensures equal atoms of each element on both sides (with state symbols).

Question 30

How do you calculate relative formula mass (Mr)?

Answer 30

Sum of Ar of all atoms in the formula.

Question 31

What is a mole?

Answer 31

The unit for amount of substance, containing 6.02 × 10²³ particles.

Question 32

How do you find reacting masses?

Answer 32

Using balanced equations, molar ratios, and Ar/Mr.

Question 33

How is percentage yield calculated?

Answer 33

(Actual yield / Theoretical yield) × 100%.

Question 34

What are empirical and molecular formulas?

Answer 34

* Empirical: simplest whole-number ratio * Molecular: actual number of atoms

Question 35

How to determine the formula of a metal oxide?

Answer 35

By combustion or reduction, measuring masses before and after.

Question 36

How are ions formed?

Answer 36

By electron loss (metals) or gain (non-metals).

Question 37

What are common positive ions (cations)?

Answer 37

* Na⁺ * K⁺ * Ca²⁺ * Ag⁺ * Cu²⁺ * Fe²⁺ * Fe³⁺ * Pb²⁺ * Zn²⁺ * H⁺

Question 38

What are common negative ions (anions)?

Answer 38

* OH⁻ * NO₃⁻ * SO₄²⁻ * CO₃²⁻ * Cl⁻ * Br⁻ * I⁻ * NH₄⁺

Question 39

How do you write formulae for ionic compounds?

Answer 39

Combine ions in ratios that balance total charge to zero.

Question 40

Why do ionic compounds have high melting points?

Answer 40

Due to strong electrostatic forces in giant ionic lattices.

Question 41

Do ionic compounds conduct electricity?

Answer 41

Yes, when molten or in solution, but not as solids.

Question 42

How is a covalent bond formed?

Answer 42

By sharing a pair of electrons between atoms.

Question 43

What is a dot-and-cross diagram?

Answer 43

A visual representation showing shared electrons, with dots and crosses for different atoms.

Question 44

How do we represent molecules like H₂, O₂, N₂, HCl, H₂O, CO₂?

Answer 44

Using structural or displayed formulas showing bonds and lone pairs.

Question 45

Why do substances with simple molecular structures have low melting and boiling points?

Answer 45

Because intermolecular forces are weak.

Question 46

How does molecular mass affect melting and boiling points?

Answer 46

Higher molecular mass generally means higher melting and boiling points.

Question 47

Why are giant covalent structures solid with high melting points?

Answer 47

Due to strong covalent bonds throughout the structure.

Question 48

How do structures of diamond, graphite, and fullerenes differ?

Answer 48

* Diamond: 3D covalent network (hard, high melting point) * Graphite: layers of hexagonal rings (soft, conducts electricity) * Fullerenes: molecules with curved surfaces.

Question 49

Do covalent compounds conduct electricity?

Answer 49

Usually no, except some with delocalized electrons (like graphite).