Topic – 8.1
Fig. 1.1 shows part of the Periodic Table.
Answer the following questions using only the elements in Fig. 1.1. Each symbol of the element may be used once, more than once or not at all.
Give the symbol of the element that:
(a)(i) produces a lilac colour in a flame test
(a)(ii) has an atom with only two occupied electron shells
(a)(iii) is an unreactive gas
(a)(iv) forms an ion that gives a white precipitate after the addition of excess sodium hydroxide
(a)(v) forms an ion with a charge of 2-
(a)(vi) is added to iron to make stainless steel.
(b) Stainless steel is a mixture. State two characteristics of a mixture.
▶️ Answer/Explanation
(a)(i) K (Potassium)
Potassium is well known for producing a lilac (pale purple) color in flame tests, which is a characteristic test for this element.
(a)(ii) F (Fluorine)
Fluorine has an atomic number of 9, with electron configuration 2,7. This means it has electrons in only two shells (K and L shells).
(a)(iii) Ar (Argon)
Argon is a noble gas in Group VIII (18) which is chemically unreactive due to its complete outer electron shell.
(a)(iv) Ca (Calcium)
Calcium forms Ca²⁺ ions which react with sodium hydroxide to form white calcium hydroxide precipitate, Ca(OH)₂, which remains insoluble even in excess NaOH.
(a)(v) S (Sulfur)
Sulfur forms S²⁻ ions (sulfide ions) with a 2- charge, as it gains two electrons to achieve a stable electron configuration.
(a)(vi) Ni (Nickel)
Nickel is commonly added to iron to make stainless steel, which improves its corrosion resistance and mechanical properties.
(b) Any two of:
- Contains two or more different substances not chemically bonded
- Does not have a fixed amount of each substance in it (has variable composition)
- Substances in mixture can be separated by physical methods
- Substances in mixture keep their own chemical properties
These are fundamental characteristics that distinguish mixtures from compounds. In stainless steel, the iron and nickel (and often chromium) retain their individual properties and can be separated by physical means.
Topic – 2.5
Nitrogen molecules are diatomic.
(a) (i) State the meaning of the term diatomic.
(ii) State the percentage of nitrogen in clean, dry air.
(b) Ammonia has a simple molecular structure. Complete Fig. 2.1 to show the dot-and-cross diagram for a molecule of ammonia. Show outer shell electrons only.
(c) Sodium chloride has a giant ionic structure of positive and negative ions.
(i) State the general name given to any positive ion.
(ii) State one physical property of an ionic compound.
(d) Graphite is used as an electrode.
(i) State one other use of graphite.
(ii) Choose the correct statement that describes the structure and bonding in graphite.
▶️ Answer/Explanation
(a) (i) A diatomic molecule consists of two atoms chemically bonded together. Many elements like nitrogen (N₂), oxygen (O₂), and hydrogen (H₂) exist as diatomic molecules in their natural state.
(ii) Nitrogen makes up approximately 78% of clean, dry air by volume. The remaining 21% is mostly oxygen, with about 1% being other gases like argon and carbon dioxide.
(b) The dot-and-cross diagram for ammonia (NH₃) should show:
- Nitrogen (N) with 5 valence electrons (2 lone pairs and 3 bonding electrons)
- Each hydrogen (H) with 1 valence electron
- Three covalent bonds between nitrogen and each hydrogen (shared electron pairs)
- One lone pair remaining on the nitrogen atom
The final structure should show the nitrogen at the center with three hydrogen atoms bonded to it and one lone pair on nitrogen.
(c) (i) A positive ion is called a cation. Cations are formed when atoms lose electrons, resulting in a net positive charge.
(ii) Ionic compounds typically have high melting and boiling points due to the strong electrostatic forces between oppositely charged ions. They also conduct electricity when molten or dissolved in water because the ions become free to move.
(d) (i) Graphite is commonly used as a lubricant because its layered structure allows the sheets to slide over one another easily. It’s also used in pencils (as the “lead”) and as a moderator in nuclear reactors.
(ii) The correct description of graphite’s structure is giant covalent. Graphite consists of layers of carbon atoms arranged in hexagonal rings, with strong covalent bonds within each layer but weak van der Waals forces between layers.
Topic – 10.1
(a) Polluted water can contain harmful substances such as plastics and phosphates.
State two other types of harmful substance in polluted water.
(b) Table 3.1 shows the masses of ions, in mg, present in a 1000 cm3 sample of polluted water.
Answer these questions using the information from Table 3.1.
(i) Name the negative ion that has the lowest concentration.
(ii) State the name of the NO3– ion.
(iii) Calculate the mass of sodium ions in 250 cm3 of polluted water.
mass = ______ mg
(c) Fig. 3.1 shows some of the stages in the treatment of the domestic water supply.
(i) Complete Fig. 3.1 by adding the final stage.
(ii) State why carbon is added to drinking water.
(d) Describe how to test the purity of water using melting point.
(e) Complete the symbol equation for the reaction of phosphorus(V) chloride, PCl5, with water.
2PCl5 + 8H2O → ….H3PO4 + ….HCl
▶️ Answer/Explanation
(a) Any two of: metal compounds, sewage, nitrates
Polluted water can contain various harmful substances beyond plastics and phosphates. Metal compounds from industrial waste, sewage containing organic matter and pathogens, and nitrates from agricultural runoff are common contaminants that make water unsafe for consumption or harmful to aquatic life.
(b)(i) bromide
Looking at Table 3.1, the bromide ion (Br–) has the lowest concentration at 0.3 mg per 1000 cm3 among all the negative ions listed.
(b)(ii) nitrate
The NO3– ion is called nitrate, which is a common polyatomic ion containing nitrogen and oxygen.
(b)(iii) 2.3 mg
Calculation: The table shows 9.2 mg of Na+ in 1000 cm3. For 250 cm3, the mass would be (9.2 mg × 250)/1000 = 2.3 mg.
(c)(i) chlorination
The final stage in water treatment is typically chlorination, where chlorine is added to kill any remaining bacteria or pathogens in the water.
(c)(ii) to remove tastes/odors
Activated carbon is added to water treatment processes primarily to adsorb and remove unpleasant tastes and odors caused by organic compounds or chlorine byproducts.
(d) Heat the water sample to its melting point (or cool to freezing point) and measure the temperature. Pure water will melt/freeze at exactly 0°C, while impure water will melt/freeze at a lower temperature or over a range of temperatures.
This works because impurities lower the melting/freezing point of water (freezing point depression). The more impurities present, the greater the deviation from 0°C.
(e) 2PCl5 + 8H2O → 2H3PO4 + 10HCl
Balancing the equation:
Phosphorus atoms: 2 on left (in 2PCl5) → 2 on right (2H3PO4)
Chlorine atoms: 10 on left (2×5) → 10 on right (10HCl)
Hydrogen atoms: 16 on left (8×2) → 6 (from H3PO4) + 10 (from HCl) = 16 on right
Oxygen atoms: 8 on left (8×1) → 8 on right (2×4 from H3PO4)
Topic – 11.5
(a) Fig. 4.1 shows the displayed formula of compound A.
(i) Explain why compound A is described as unsaturated.
(ii) Explain why compound A is a hydrocarbon.
(iii) Deduce the molecular formula of compound A.
(b) Compound A reacts with steam to produce an alcohol.
(i) State the general formula for the homologous series of alcohols.
(ii) Ethanol is an alcohol which can be manufactured by fermentation.
– Name two substances needed for fermentation.
– Give two conditions needed for fermentation.
(iii) State one use of ethanol.
(c) A compound in the same homologous series as compound A reacts with ozone, \( O_3 \), to form compound B.
(i) Define the term homologous series.
(ii) The molecular formula for compound B is \( C_6H_{12}O_3 \).
Complete Table 4.1 to calculate the relative molecular mass of \( C_6H_{12}O_3 \).
relative molecular mass = ………………………… [2]
▶️ Answer/Explanation
(a)(i) C=C bond / carbon-carbon double bond
Detailed explanation: An unsaturated compound contains at least one double or triple bond between carbon atoms. The presence of a C=C double bond (as shown in Fig. 4.1) means the compound is unsaturated because it can undergo addition reactions where atoms add across the double bond.
(a)(ii) contains carbon and hydrogen only / contains carbon and hydrogen and no other element
Detailed explanation: A hydrocarbon is defined as any compound that consists exclusively of carbon and hydrogen atoms. Since compound A only contains these two elements (as evident from its displayed formula), it qualifies as a hydrocarbon.
(a)(iii) \( C_6H_{10} \)
Detailed explanation: By counting the atoms in the displayed formula (Fig. 4.1), we can determine the molecular formula. The structure shows 6 carbon atoms and 10 hydrogen atoms, giving the molecular formula \( C_6H_{10} \).
(b)(i) \( C_nH_{2n+1}OH \)
Detailed explanation: The general formula for alcohols is \( C_nH_{2n+1}OH \), where n represents the number of carbon atoms. This formula accounts for the hydroxyl (-OH) functional group characteristic of alcohols.
(b)(ii) substances needed: (aqueous) glucose and yeast
conditions: any two of: absence of oxygen, 25-45°C, aqueous/in water
Detailed explanation: Fermentation requires glucose as the substrate and yeast as the microorganism that carries out the process. The optimal conditions include: anaerobic conditions (absence of oxygen), warm temperatures (25-45°C) that allow yeast enzymes to function efficiently, and an aqueous environment for the reaction to occur.
(b)(iii) solvent / fuel
Detailed explanation: Ethanol has multiple uses including as a solvent in various industries (perfumes, medicines) and as a biofuel or fuel additive due to its combustible properties.
(c)(i) family of similar chemical compounds / compounds with similar chemical properties with same functional group
Detailed explanation: A homologous series is a group of organic compounds that share: 1) the same general formula, 2) similar chemical properties, and 3) a gradual change in physical properties. Members differ by a \( CH_2 \) unit and have the same functional group.
(c)(ii) 132
Detailed explanation: To calculate the relative molecular mass of \( C_6H_{12}O_3 \):
Carbon: 6 atoms × 12 = 72
Hydrogen: 12 atoms × 1 = 12
Oxygen: 3 atoms × 16 = 48
Total = 72 + 12 + 48 = 132
The completed table would show 12 hydrogen atoms and 3 oxygen atoms.
Topic – 8.3
(a) Table 5.1 shows some properties of five halogens.
Use the information in Table 5.1 to predict:
(i) the melting point of iodine
(ii) the atomic radius of fluorine
(iii) the physical state of bromine at 0°C. Give a reason for your answer.
(b) Aqueous chlorine reacts with aqueous potassium iodide.
(i) Complete the word equation for this reaction.
chlorine + potassium iodide → ………………………………………….. + …………………………………………..
(ii) Explain why aqueous iodine does not react with aqueous potassium bromide.
(c) Fluorine reacts with hot concentrated sodium hydroxide to produce sodium fluoride, water and oxygen.
(i) Complete the symbol equation for this reaction.
\( 2F_2 + 4NaOH \rightarrow ….NaF + 2H_2O + …… \)
(ii) Describe a test for oxygen.
▶️ Answer/Explanation
(a)(i) Between −5°C and 180°C inclusive
Looking at the trend in melting points down the group (fluorine to astatine), we see they increase steadily. Iodine’s melting point should be between bromine’s (−7°C) and astatine’s (302°C). A reasonable prediction would be around 113°C (actual value is 113.7°C).
(a)(ii) Between 0.098 nm and 0.01 nm
Atomic radius increases down the group. Fluorine, being at the top, should have the smallest radius. From the given data, chlorine is 0.099 nm, so fluorine should be slightly smaller.
(a)(iii) liquid (1)
temperature between −7°C and +59°C / 0°C is between the melting and boiling point (1)
Bromine’s melting point is −7°C and boiling point is +59°C. At 0°C (between these two points), bromine would be in its liquid state.
(b)(i) iodine (1)
potassium chloride (1)
This is a displacement reaction where the more reactive chlorine displaces iodine from potassium iodide:
\( Cl_2 + 2KI \rightarrow I_2 + 2KCl \)
(b)(ii) iodine is less reactive than bromine / bromine is more reactive than iodine / bromine is higher in the electrochemical series than iodine
In halogen displacement reactions, a more reactive halogen can displace a less reactive one from its compound. Since iodine is less reactive than bromine, it cannot displace bromine from potassium bromide.
(c)(i) 4(NaF) (1)
\( O_2 \) (1)
The balanced equation is:
\( 2F_2 + 4NaOH \rightarrow 4NaF + 2H_2O + O_2 \)
(c)(ii) glowing splint (1)
relights (1)
Oxygen supports combustion. The standard test is to insert a glowing splint into the gas. If oxygen is present, the splint will relight.
Topic – 9.1
This question is about metals.
(a) Metals are good electrical conductors.
State three other typical physical properties of metals.
(b) (i) Complete Table 6.1 to show the number of electrons, neutrons and protons in the potassium atom and the nickel ion shown.
(ii) Write the electronic configuration of the potassium atom.
(c) Choose one property from the list that shows that nickel is a transition element.
Tick (✓) one box.
- □ has a low density
- □ forms coloured compounds
- □ has a low melting point
- □ does not act as a catalyst
(d) Nickel can be manufactured by reducing nickel(II) oxide with carbon monoxide and hydrogen.
\[ 2NiO + CO + H_2 \rightarrow 2Ni + H_2O + CO_2 \]
Explain how this equation shows that nickel(II) oxide is reduced.
(e) Table 6.2 shows the observations when four different metals are heated with steam.
Put the four metals in order of their reactivity.
Put the least reactive metal first.
▶️ Answer/Explanation
(a) Any three of:
- Malleable (can be hammered into sheets)
- Ductile (can be drawn into wires)
- High melting point / high boiling point
- Good thermal conductor
- Shiny/lustrous appearance
- Sonorous (produces ringing sound when struck)
(b)(i) Table 6.1 completed:
| number of electrons | number of neutrons | number of protons | |
|---|---|---|---|
| 41K | 19 | 22 (41-19) | 19 |
| 62Ni2+ | 26 (28-2) | 34 | 28 |
For potassium: Neutrons = mass number (41) – atomic number (19) = 22. Protons = atomic number = 19.
For nickel ion: Protons = atomic number = 28. Electrons = atomic number (28) – charge (2+) = 26.
(b)(ii) Electronic configuration of potassium: 2,8,8,1
Potassium (K) has atomic number 19, so its electron arrangement is: 2 electrons in first shell, 8 in second, 8 in third, and 1 in outer shell.
(c) Second box ticked: “forms coloured compounds”
This is a characteristic property of transition elements like nickel. They form colored compounds due to the presence of partially filled d-orbitals.
(d) Nickel(II) oxide loses oxygen
In the reaction, nickel(II) oxide (NiO) is converted to nickel (Ni), meaning it loses oxygen. This is the definition of reduction (loss of oxygen).
(e) Order of reactivity: niobium < copper < chromium < magnesium
The rate of oxide formation indicates reactivity with steam/oxygen. Magnesium reacts most rapidly, followed by chromium, then copper. Niobium doesn’t react at all, making it least reactive.
Topic – 7.1
This question is about acids, bases and salts.
(a) Crystals of potassium chloride can be made by reacting an acid with an alkali.
(i) Name the acid and the alkali used.
(ii) Choose from the list the type of reaction that takes place when an acid reacts with an alkali.
Draw a circle around your chosen answer.
addition neutralisation redox substitution
(iii) Thymolphthalein is an acid-base indicator.
State the colour of thymolphthalein at pH2 and at pH12.
(iv) Describe how to make dry crystals of potassium chloride from an aqueous solution of potassium chloride.
(b) Crystals of potassium chloride dissolve in water. This process is endothermic.
(i) Define the term endothermic.
(ii) Fig. 7.1 shows the reaction pathway diagram for dissolving potassium chloride in water.
Answer the following questions using the information in Fig. 7.1.
– State the meaning of the state symbol (l).
– Explain how Fig. 7.1 shows that dissolving potassium chloride in water is endothermic.
▶️ Answer/Explanation
(a)(i) acid: hydrochloric acid (1)
alkali: potassium hydroxide (1)
Detailed solution: Potassium chloride can be made by neutralization reaction between hydrochloric acid (HCl) and potassium hydroxide (KOH). The balanced equation is: \( \text{HCl} + \text{KOH} \rightarrow \text{KCl} + \text{H}_2\text{O} \).
(a)(ii) neutralisation
Detailed solution: The reaction between an acid and a base is called a neutralization reaction, where the acid and base react to form a salt and water.
(a)(iii) pH 2: colourless (1)
pH 12: blue (1)
Detailed solution: Thymolphthalein is a pH indicator that changes color around pH 9.3-10.5. In acidic conditions (pH 2), it remains colorless. In basic conditions (pH 12), it turns blue.
(a)(iv) One mark each for any two of:
• evaporate some of the water / heat to the point of crystallisation / heat until crystals seen
• filter off crystals / pick out crystals
• dry crystals with filter paper
Detailed solution: To obtain dry KCl crystals from solution: First, heat the solution to evaporate water until crystals begin to form (point of crystallization). Then, filter the solution to separate the crystals from remaining liquid. Finally, dry the crystals between filter papers to remove any residual moisture.
(b)(i) absorption of thermal energy
Detailed solution: An endothermic process is one that absorbs heat energy from the surroundings. When KCl dissolves in water, it takes in heat, causing the temperature of the solution to decrease.
(b)(ii) state symbol: liquid (1)
explanation: the energy of the products is higher than the energy of the reactants / the energy of KCl + H₂O is greater than the energy of KCl (aq) (1)
Detailed solution: The (l) symbol indicates the substance is in liquid state. The diagram shows an endothermic process because the products (KCl in solution) have higher energy than the reactants (solid KCl and liquid water). This upward energy change means energy is absorbed during dissolution.
Topic – 6.2
(a) A student investigates the reaction of small pieces of zinc with excess dilute sulfuric acid of three different concentrations. The time taken for each reaction to finish is recorded.
The three concentrations of the acid are:
- 0.2 mol/dm3
- 0.4 mol/dm3
- 0.8 mol/dm3
All other conditions stay the same.
Table 8.1 shows the time taken for each reaction to finish.
(i) Complete Table 8.1 by writing the concentrations in the first column.
(ii) Describe the effect on the time taken for the reaction to finish when the reaction is carried out in the presence of a catalyst. All other conditions stay the same.
(iii) Describe the effect on the time taken for the reaction to finish when larger pieces of zinc are used instead of small pieces of zinc. All other conditions stay the same.
(b) Dilute sulfuric acid is electrolysed using inert electrodes.
(i) Name the products at the positive and negative electrodes.
(ii) Choose from the list the metal used as an inert electrode. Draw a circle around your chosen answer.
calcium magnesium platinum sodium
(c) Zinc is a solid at room temperature. Describe the arrangement and separation of the particles in solid zinc.
▶️ Answer/Explanation
(a)(i) The concentrations should be ordered from slowest to fastest reaction time:
- 0.2 mol/dm3 – 92 s (slowest)
- 0.4 mol/dm3 – 46 s
- 0.8 mol/dm3 – 23 s (fastest)
This shows that higher acid concentrations lead to faster reaction times as there are more reactant particles available for collisions.
(a)(ii) The presence of a catalyst would decrease the time taken for the reaction to finish. Catalysts provide an alternative reaction pathway with lower activation energy, increasing the rate of reaction without being consumed.
(a)(iii) Using larger pieces of zinc would increase the time taken for the reaction to finish. Larger pieces have smaller surface area to volume ratio, meaning fewer zinc particles are exposed to the acid at any time, slowing the reaction.
(b)(i) Positive electrode (anode): oxygen
Negative electrode (cathode): hydrogen
During electrolysis of dilute sulfuric acid, water molecules decompose to form these gases.
(b)(ii) The correct inert electrode is platinum. Platinum is used because it doesn’t react with the electrolyte or products of electrolysis, unlike the other metals listed which would react.
(c) Arrangement: The particles in solid zinc are arranged in a regular, repeating pattern (crystalline structure).
Separation: The particles are closely packed together and touching, with strong metallic bonds between them.
This regular, close arrangement explains why zinc is dense and maintains a fixed shape at room temperature.