Analysis For Compounds

Question 1

What is periodicity?

Answer 1

The repeating trends in the properties of elements across the periodic table due to the arrangement of electrons.

Question 2

Why does atomic radius decrease across a period?

Answer 2

Increasing nuclear charge pulls electrons closer to the nucleus, reducing atomic radius.

Question 3

Why does ionisation energy increase across a period?

Answer 3

Increasing nuclear charge and decreasing atomic radius make it harder to remove electrons.

Question 4

Why does electronegativity increase across a period?

Answer 4

Increasing nuclear charge and decreasing atomic radius increase the attraction for bonding electrons.

Question 5

Why do melting points of metals decrease down Group 2?

Answer 5

Metallic bonding weakens as the atomic radius increases.

Question 6

What is the trend in reactivity of Group 2 elements?

Answer 6

Reactivity increases down the group due to decreasing ionisation energy.

Question 7

Why is magnesium a special case in Group 2?

Answer 7

Magnesium has a smaller atomic radius and higher ionisation energy, making it less reactive than other Group 2 elements. It also forms a protective oxide layer.

Question 8

What is the trend in melting points down Group 2?

Answer 8

Melting points decrease due to weaker metallic bonding as the atomic radius increases.

Question 9

Why does ionisation energy decrease down Group 2?

Answer 9

Ionisation energy decreases due to increased shielding and atomic radius, making it easier to remove outer electrons.

Question 10

Why does reactivity increase down Group 2?

Answer 10

Reactivity increases because the outer electrons are further from the nucleus and experience more shielding, making them easier to lose.

Question 11

Write the equation for the reaction of magnesium with oxygen.

Answer 11

2Mg + O2 = 2MgO.

Question 12

Write the equation for the reaction of calcium with chlorine

Answer 12

Ca + Cl2 = CaCl2.

Question 13

Write the equation for the reaction of barium with water.

Answer 13

Ba + 2H2O = Ba(OH)2 + H2.

Question 14

Why does magnesium react slowly with cold water?

Answer 14

Magnesium forms a protective oxide layer that slows its reaction with cold water.

Question 15

Write the equation for the reaction of magnesium with steam.

Answer 15

Mg + H2O (steam) = MgO + H2.

Question 16

Write the equation for the reaction of magnesium oxide with water.

Answer 16

MgO + H2O = Mg(OH)2.

Question 17

Write the equation for the reaction of calcium oxide with dilute hydrochloric acid.

Answer 17

CaO + 2HCl = CaCl2 + H2O.

Question 18

What is observed when barium hydroxide reacts with sulfuric acid?

Answer 18

A white precipitate of barium sulfate forms: Ba(OH)2 + H2SO4 = BaSO4 + 2H2O.

Question 19

Why is magnesium hydroxide basically insoluble in water?

Answer 19

Magnesium hydroxide has a high lattice energy due to the small size and high charge density of the Mg2+ ion.

Question 20

What is the trend in solubility of Group 2 hydroxides?

Answer 20

Solubility increases down the group (e.g., Mg(OH)2 is sparingly soluble, while Ba(OH)2 is more soluble).

Question 21

What is the trend in solubility of Group 2 sulfates?

Answer 21

Solubility decreases down the group (e.g., MgSO4 is soluble, while BaSO4 is insoluble).

Question 22

Why is barium sulfate used in medical imaging?

Answer 22

It is insoluble and opaque to X-rays, making it useful for imaging the digestive system.

Question 23

Why does thermal stability of Group 1 and 2 carbonates increase down the group?

Answer 23

Larger cations have lower charge density, causing less polarisation of the carbonate ion and greater stability.

Question 24

Write the equation for the thermal decomposition of magnesium carbonate

Answer 24

MgCO3 = MgO + CO2.

Question 25

Why does thermal stability of Group 1 and 2 nitrates increase down the group?

Answer 25

Larger cations have lower charge density, causing less polarisation of the nitrate ion and greater stability.

Question 26

Write the equation for the thermal decomposition of calcium nitrate.

Answer 26

2Ca(NO3)2 = 2CaO + 4NO2 + O2.

Question 27

Why do Group 1 and 2 compounds produce characteristic flame colours?

Answer 27

Electrons are excited to higher energy levels and emit light of specific wavelengths when they return to the ground state.

Question 28

Why do melting and boiling points increase down Group 7?

Answer 28

Larger molecules have stronger van der Waals forces between them.

Question 29

Why does electronegativity decrease down Group 7?

Answer 29

Atomic radius increases, and the attraction for bonding electrons decreases.

Question 30

Why does reactivity decrease down Group 7?

Answer 30

Atomic radius increases, and the ability to gain electrons decreases.

Question 31

Write the equation for the reaction of chlorine with potassium iodide.

Answer 31

Cl2 + 2KI = 2KCl + I2.

Question 32

What is observed when chlorine reacts with water?

Answer 32

Chlorine disproportionates to form hydrochloric acid and chloric(I) acid: Cl2 + H2O = HCl + HClO.

Question 33

Write the equation for the reaction of chlorine with cold, dilute sodium hydroxide.

Answer 33

Cl2 + 2NaOH = NaCl + NaClO + H2O.

Question 34

What is the use of chlorine in water treatment?

Answer 34

Chlorine kills bacteria and disinfects water.

Question 35

What is observed when silver nitrate is added to bromide ions (Br-)?

Answer 35

A cream precipitate of AgBr forms, which is insoluble in dilute NH3. Soluble in conc NH3

Question 36

What is observed when silver nitrate is added to iodide ions (I-)?

Answer 36

A yellow precipitate of AgI forms, which is insoluble in dilute NH3.

Question 37

Write the equation for the reaction of hydrogen chloride with ammonia.

Answer 37

HCl + NH3 = NH4Cl.

Question 38

How do you test for carbonate ions (CO3^2-)?

Answer 38

Add dilute acid; effervescence of CO2 gas is observed.

Question 39

How do you test for sulfate ions (SO4^2-)?

Answer 39

Add acidified BaCl2; a white precipitate of BaSO4 forms.

Question 40

How do you test for ammonium ions (NH4+)?

Answer 40

Add NaOH and heat; ammonia gas is released, which turns damp red litmus paper blue.

Question 41

Why is fluorine the most reactive halogen?

Answer 41

It has the smallest atomic radius and highest electronegativity.

Question 42

What is the trend in reducing ability of hydrogen halides?

Answer 42

Reducing ability increases down the group (HF is the weakest, HI is the strongest).

Question 43

Write the equation for the reaction of solid sodium chloride with concentrated sulfuric acid.

Answer 43

NaCl + H2SO4 = NaHSO4 + HCl.

Question 44

What is the trend in thermal stability of Group 1 and 2 nitrates?

Answer 44

Thermal stability increases down the group.

Question 45

Why does magnesium react slowly with cold water?

Answer 45

It forms a protective oxide layer that slows the reaction.

Question 46

What is the flame colour for magnesium ions (Mg2+)?

Answer 46

Magnesium does not produce a characteristic flame colour. Flame of magnesium is out of human eye spectrum’s

Question 47

Predict the physical state of astatine at room temperature.

Answer 47

Solid (trend in Group 7 shows increasing melting and boiling points).

Question 48

Predict the reactivity of fluorine compared to chlorine.

Answer 48

Fluorine is more reactive due to its smaller atomic radius and higher electronegativity.

Question 49

Predict the colour of astatine in solution.

Answer 49

Darker than iodine (likely black or very dark purple).

Question 50

Describe an experiment to show the thermal decomposition of Group 1 and 2 nitrates.

Answer 50

Heat the nitrate in a test tube and observe the gas evolved (e.g., brown NO2 gas for Group 2 nitrates).

Question 51

Describe an experiment to show flame colours of Group 1 and 2 compounds

Answer 51

Dip a nichrome wire in the compound and place it in a Bunsen flame. Observe the flame colour.

Question 52

What is the flame test for lithium ions (Li⁺)?

Answer 52

Crimson red flame.

Question 53

What is the flame test for sodium ions (Na⁺)?

Answer 53

Yellow flame.

Question 54

What is the flame test for potassium ions (K⁺)?

Answer 54

Lilac flame.

Question 55

What is the flame test for calcium ions (Ca²⁺)?

Answer 55

Brick red flame.

Question 56

What is the flame test for barium ions (Ba²⁺)?

Answer 56

Green flame.

Question 57

How do you test for carbonate ions (CO₃²⁻)?

Answer 57

Add dilute acid (e.g., HCl). Observation: Effervescence of CO₂ gas (turns limewater cloudy).

Question 58

How do you test for sulfate ions (SO₄²⁻)?

Answer 58

Add acidified BaCl₂ solution. Observation: White precipitate of BaSO₄ forms.

Question 59

How do you test for chloride ions (Cl⁻)?

Answer 59

Add AgNO₃ solution, then dilute NH₃. Observation: White precipitate of AgCl forms, which dissolves in dilute NH₃.

Question 60

How do you test for bromide ions (Br⁻)?

Answer 60

Add AgNO₃ solution, then dilute NH₃. Observation: Cream precipitate of AgBr forms, which is not soluble in dilute NH₃. solube in concentrated NH3 only

Question 61

How do you test for iodide ions (I⁻)?

Answer 61

Add AgNO₃ solution, then dilute NH₃. Observation: Yellow precipitate of AgI forms, which is insoluble in dilute NH₃.

Question 62

How do you test for ammonia gas (NH₃)?

Answer 62

Use damp red litmus paper. Observation: Litmus paper turns blue.

Question 63

How do you test for hydrogen gas (H₂)?

Answer 63

Hold a lit splint near the gas. Observation: A squeaky pop sound is heard.

Question 64

How do you test for chlorine gas (Cl₂)?

Answer 64

Use damp blue litmus paper. Observation: Litmus paper turns white (bleached)

Question 65

How do you test for nitrate ions (NO₃⁻)?

Answer 65

Add NaOH solution and aluminium foil, then heat. Observation: Ammonia gas is produced (turns damp red litmus paper blue).

Question 66

How do you test for hydrogencarbonate ions (HCO₃⁻)?

Answer 66

Add dilute acid. Observation: Effervescence of CO₂ gas (turns limewater cloudy).

Question 67

How do you test for alkenes?

Answer 67

Add bromine water. Observation: Bromine water turns colourless.

Question 68

How do you test for alcohols?

Answer 68

Add acidified potassium dichromate(VI) solution and heat. Observation: Orange solution turns green (for primary and secondary alcohols).

Question 69

How do you test for aluminium ions (Al³⁺)

Answer 69

Add NaOH solution. Observation: White precipitate forms, which dissolves in excess NaOH.