Area 1: Chemical changes and structure

Name the bonding and the forces between particles before you explain a property: a trend or a boiling point follows from what has to be overcome.

A lesson for this area

Multiple choice, Section 1 style

Question 1

Covalent radius decreases across period 3 from sodium to chlorine. Which statement explains this trend?

Question 2

Which list puts the atoms in order of increasing covalent radius?

Question 3

Which equation represents the first ionisation energy of chlorine?

Question 4

The first ionisation energy decreases down group 2 from beryllium to barium. Which statement explains this?

Question 5

The first four ionisation energies of element X are 578, 1817, 2745 and 11 577 kJ mol⁻¹. In which group of the periodic table is X?

Question 6

The first three ionisation energies of calcium are 590, 1145 and 4912 kJ mol⁻¹. How much energy is needed to turn 0.250 mol of gaseous calcium atoms into gaseous Ca²⁺ ions?

Question 7

Without using any data, which of these changes needs the most energy for one mole of the particle shown?

Question 8

Why is the electronegativity of fluorine greater than that of iodine?

Question 9

Electronegativity increases across period 2 from lithium to fluorine. Which pair of changes across the period explains this?

Question 10

Which element in the first 20 of the periodic table has a covalent network structure?

Question 11

What holds two atoms together in a covalent bond?

Question 12

Use these electronegativities: H 2.2, C 2.6, N 3.0, O 3.4, S 2.6, Cl 3.2. Which bond is the most polar?

Question 13

The electronegativity of carbon is 2.6 and that of hydrogen is 2.2. Using these values, how are the partial charges shown on the atoms of a C-H bond?

Question 14

Use these electronegativities: K 0.8, Na 0.9, Mg 1.3, Al 1.6, F 4.0, Cl 3.2, I 2.7. Which compound has the greatest ionic character?

Question 15

Titanium(IV) chloride is a colourless liquid at room temperature. It boils at 136 °C and the liquid does not conduct electricity. What can be deduced about it?

Question 16

Element E melts at 98 °C. It conducts electricity both as a solid and as a liquid. What is its bonding and structure?

Question 17

What is the formula of ammonium dichromate?

Question 18

Use these electronegativities: H 2.2, C 2.6, O 3.4, F 4.0, S 2.6, Cl 3.2. Which bond is pure covalent even though it joins atoms of two different elements?

Question 19

Compound Q melts at 1713 °C, is insoluble in water and does not conduct electricity as a solid or when molten. What is its structure?

Question 20

How do London dispersion forces arise?

Question 21

Bromine, Br₂, boils at 59 °C and chlorine, Cl₂, boils at −34 °C. Which statement explains the difference?

Question 22

Hydrogen chloride, HCl, and fluorine, F₂, both have 18 electrons. HCl boils at −85 °C and F₂ at −188 °C. Why is the boiling point of HCl higher?

Question 23

Iodine monochloride, ICl, and bromine, Br₂, each have 70 electrons. The electronegativity of iodine is 2.7 and that of chlorine is 3.2. Which correctly compares their boiling points?

Question 24

Propane (CH₃CH₂CH₃), methoxymethane (CH₃OCH₃) and ethanol (CH₃CH₂OH) each have 26 electrons. Which list puts them in order of increasing boiling point?

Question 25

Water, H₂O, boils at 100 °C, but hydrogen sulfide, H₂S, boils at −60 °C although an H₂S molecule has more electrons. Why?

Question 26

Why is ice less dense than liquid water at 0 °C?

Question 27

Which molecule contains polar bonds but is non-polar overall?

Question 28

Which of these liquids is the most viscous at room temperature?

Question 29

Which substance is likely to dissolve in hexane but not in water?

Question 30

Zinc reacts with copper(II) sulfate solution: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). Which species is the oxidising agent?

Question 31

Which element is most likely to act as a reducing agent?

Question 32

Dichromate ions are reduced to chromium(III) ions in acid: Cr₂O₇²⁻(aq) + xH⁺(aq) + ye⁻ → 2Cr³⁺(aq) + zH₂O(l). What are x, y and z?

Question 33

In acid, vanadate ions, VO₃⁻, can be reduced to V²⁺ ions. Which ion-electron equation is balanced?

Question 34

Use these ion-electron equations: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O and Fe²⁺ → Fe³⁺ + e⁻. What is the balanced redox equation?

Question 35

In a blast furnace, iron(III) oxide reacts with carbon monoxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Which statement is correct?

Question 36

Which of these ion-electron equations shows an oxidation?

Question 37

Acidified potassium dichromate solution is added to a reducing agent and warmed. What colour change is seen?

Question 38

These reductions are listed in order: the oxidising agent on the left becomes stronger down the list. I₂ + 2e⁻ → 2I⁻ Fe³⁺ + e⁻ → Fe²⁺ Br₂ + 2e⁻ → 2Br⁻ Which pair of solutions react together?

Question 39

Why can oxidising agents be used to bleach clothes and hair?

Question 40

The electronegativity of sulfur is 2.6, chlorine 3.2 and bromine 3.0. Which statement explains why chlorine has the highest value of the three?

Question 41

Ammonia, NH₃, boils at −33 °C, phosphine, PH₃, at −88 °C and stibine, SbH₃, at −17 °C. Which statement explains this pattern?

Question 42

Acidified dichromate oxidises ethanol to ethanoic acid. The ion-electron equations are Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O and C₂H₅OH + H₂O → CH₃COOH + 4H⁺ + 4e⁻. What is the redox equation?

Question 43

The first four ionisation energies of element Z are 1086, 2353, 4620 and 6223 kJ mol⁻¹. Which conclusion about Z is supported by these values?

Question 44

The first four ionisation energies of aluminium are 578, 1817, 2745 and 11 577 kJ mol⁻¹. How much energy is needed to remove all of the outer electrons from 1.00 g of gaseous aluminium atoms? (Relative atomic mass: Al 27.0)

Question 45

Aluminium fluoride stays solid until about 1290 °C, but aluminium chloride turns to vapour at 180 °C. Electronegativities: Al 1.6, F 4.0, Cl 3.2. Which statement explains the difference?

Question 46

The boiling points of the hydrogen halides are HF 20 °C, HCl −85 °C, HBr −67 °C and HI −35 °C. Which statement explains why HCl has the lowest boiling point of the four?

Question 47

Acidified dichromate oxidises iron(II) ions: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O and Fe²⁺ → Fe³⁺ + e⁻. What volume of 0.0200 mol l⁻¹ dichromate solution is needed to oxidise 0.00600 mol of iron(II) ions?

Question 48

These reductions are listed in order: the oxidising agent on the left becomes stronger down the list. Sn⁴⁺ + 2e⁻ → Sn²⁺ I₂ + 2e⁻ → 2I⁻ Fe³⁺ + e⁻ → Fe²⁺ Br₂ + 2e⁻ → 2Br⁻ Which substance can oxidise Sn²⁺ ions but cannot oxidise Fe²⁺ ions?

Question 49

Hydrazine, N₂H₄, and ethane, C₂H₆, each have 18 electrons. Hydrazine boils at 114 °C and ethane at −89 °C. Which statement explains this and predicts how hydrazine behaves with water?

Section 2 questions, then open-ended questions

Trends across period 3Section 2 question · 7 marks

The table gives the covalent radius and electronegativity of some period 3 elements. The first four ionisation energies of aluminium are 578, 1817, 2745 and 11 577 kJ mol⁻¹.

Period 3 elements
Element	Covalent radius (pm)	Electronegativity
Sodium	160	0.9
Magnesium	140	1.3
Aluminium	124	1.6
Silicon	114	1.9
Sulfur	104	2.6
Chlorine	100	3.2

(a) Explain why the covalent radius decreases from sodium to chlorine. [2]

0 words · one point a mark

(b) Which element in the table attracts the electrons in a covalent bond most strongly? [1]

(d) Explain why the fourth ionisation energy of aluminium is much larger than the third. [2]

0 words · one point a mark

Boiling points of hydridesSection 2 question · 7 marks

The table shows the boiling points of the hydrides of group 6 elements and the number of electrons in each molecule.

Group 6 hydrides
Hydride	Number of electrons	Boiling point (°C)
H₂O	10	100
H₂S	18	−60
H₂Se	36	−41
H₂Te	54	−2

(a) Explain why the boiling point increases from H₂S to H₂Te. [2]

0 words · one point a mark

(b) Explain why the boiling point of water is far higher than the trend in the other hydrides suggests. [2]

0 words · one point a mark

(c) Hydrogen fluoride, HF, boils at 20 °C but hydrogen chloride, HCl, boils at −85 °C. Name the intermolecular force responsible for the higher boiling point of HF. [1]

0 words · a word or a sentence

(d) Ice floats on water. Explain why ice is less dense than liquid water. [2]

0 words · one point a mark

Deducing bonding from propertiesSection 2 question · 6 marks

The table gives some properties of three substances. Electronegativities: K 0.8, I 2.7, C 2.6, Cl 3.2.

Three substances
Substance	Melting point (°C)	Conducts as a solid	Conducts when molten	Soluble in water
Potassium iodide	681	no	yes	yes
Silicon carbide	about 2700	no	no	no
Tetrachloromethane	−23	no	no	no

(a) What is the bonding and structure of silicon carbide? [1]

(b) Explain why potassium iodide conducts electricity when molten but not when solid. [2]

0 words · one point a mark

(d) Tetrachloromethane is insoluble in water. State a reason. [1]

0 words · a word or a sentence

Iron in a supplement tabletSection 2 question · 8 marks

An iron supplement tablet contains iron(II) ions. A student dissolves one tablet in dilute sulfuric acid and adds 0.0200 mol l⁻¹ potassium permanganate solution from a burette. 18.6 cm³ of permanganate solution react with all of the iron(II) ions. The redox equation is MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 4H₂O + 5Fe³⁺. (Relative atomic mass: Fe 55.8.)

(a) Write the ion-electron equation for the oxidation of iron(II) ions. [1]

0 words · a word or a sentence

(b) No indicator is added. Explain how the student can tell when all of the iron(II) ions have reacted. [2]

0 words · one point a mark

(d) Explain, in terms of electrons, why the permanganate ion is described as the oxidising agent in this reaction. [2]

0 words · one point a mark

Dry cleaningSection 2 question · 6 marks

Dry cleaners remove stains from clothes using tetrachloroethene, C₂Cl₄, instead of water. Tetrachloroethene is a liquid with four polar C-Cl bonds arranged symmetrically in a flat molecule. Grease is made of non-polar molecules. Sucrose, a sugar, has many O-H groups in each molecule.

(a) Which solvent would remove a grease stain best? [1]

(b) Explain why sucrose dissolves in water but not in tetrachloroethene. [2]

0 words · one point a mark

(d) Name the intermolecular forces that act between tetrachloroethene molecules. [1]

0 words · a word or a sentence

Household bleachSection 2 question · 7 marks

Household bleach is a solution of sodium hypochlorite, which contains ClO⁻ ions. In acid, hypochlorite ions react: ClO⁻(aq) + 2H⁺(aq) + 2e⁻ → Cl⁻(aq) + H₂O(l). Bleach must never be mixed with acidic toilet cleaners, because chlorine gas forms. Electronegativities: Na 0.9, Cl 3.2.

(a) State whether the hypochlorite ion acts as an oxidising agent or a reducing agent, and give a reason. [2]

0 words · one point a mark

(b) When bleach is mixed with acid, chloride ions are converted into chlorine. Which ion-electron equation shows this change? [1]

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(d) Use the electronegativities to explain why chlorine acts as an oxidising agent but sodium acts as a reducing agent. [2]

0 words · one point a mark

Hydrogen peroxideOpen-ended question · 3 marks

Hydrogen peroxide, H₂O₂, is sold as a dilute solution in water. Dentists use it to whiten teeth, hairdressers use it to lighten hair and it has been used to clean wounds. It slowly breaks down into water and oxygen, faster in light, so it is sold in dark bottles.

(a) Using your knowledge of chemistry, comment on the uses and properties of hydrogen peroxide. [3]

0 words · one point a mark