Substance Identification
Choose from the following substances to answer the questions:
carbon, chlorine, glucose, hydrated copper(II) sulfate, iron, magnesium sulfate, methanoic acid, methanol, nickel, silicon(IV) oxide, vanadium(V) oxide
Each substance can be used once, more than once or not at all.
(a) is a catalyst in the Haber process
(b) has a giant covalent structure
(c) changes from a blue solid to a white solid when heated
(d) removes tastes and odours during the treatment of the domestic water supply
(e) has the empirical formula CH₂O
Solutions
(a) iron
(b) silicon(IV) oxide
(c) hydrated copper(II) sulfate
(d) carbon
(e) glucose
Strategy & Concept
This question tests your knowledge of specific chemical substances and their properties. You need to recall specific facts from the syllabus.
- Haber Process: Industrial production of ammonia using an iron catalyst
- Giant Covalent Structures: Networks of atoms bonded by strong covalent bonds (diamond, graphite, silica)
- Hydrated Salts: Contain water of crystallization that can be removed by heating
- Water Treatment: Activated carbon adsorbs impurities causing tastes and odors
- Empirical Formula: Simplest whole-number ratio of atoms in a compound
Predicted Related Questions
- Name a substance with a simple molecular structure from the list
- Identify a substance that conducts electricity in the molten state (ionic compounds)
- Which substance is used as a catalyst in the Contact Process?
Calcium Carbide and Ethyne
Calcium carbide, CaC₂, reacts with water to form a flammable gas ethyne, C₂H₂, and calcium hydroxide.
(a) Construct the symbol equation for this reaction.
(b) Calcium carbide is ionic. Deduce the formula of the carbide ion.
(c) Fig. 2.1 shows the displayed formula of ethyne: H-C≡C-H
Ethyne is an unsaturated hydrocarbon.
(c)(i) Explain why ethyne is a hydrocarbon.
(c)(ii) Suggest why ethyne is unsaturated.
(c)(iii) Aqueous bromine reacts with ethyne. Predict the colour change.
(c)(iv) Draw a dot-and-cross diagram to show the electronic configuration in a molecule of ethyne.
(d) The equation for the complete combustion of ethyne is shown:
This reaction is exothermic.
(d)(i) Explain, using ideas about bond breaking and bond making, why this reaction is exothermic.
(d)(ii) Complete the reaction pathway diagram for the complete combustion of ethyne.
Solutions
(a) CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂
(b) C₂²⁻
(c)(i) It contains only hydrogen and carbon atoms.
(c)(ii) It contains a carbon-carbon triple bond.
(c)(iii) Orange/brown to colorless.
(c)(iv) Diagram showing H atoms with one electron each, C atoms with four outer electrons, and a triple bond between C atoms (three shared electron pairs).
(d)(i) More energy is released forming the bonds in the products (CO₂ and H₂O) than is absorbed breaking the bonds in the reactants (C₂H₂ and O₂).
(d)(ii) Energy profile diagram showing reactants at higher energy, products at lower energy, downward arrow for ΔH, and energy barrier for Eₐ.
Strategy & Concept
Key Concepts:
- Balancing Equations: Ensure atom conservation on both sides
- Ionic Compounds: Charges must balance (Ca²⁺ requires C₂²⁻)
- Hydrocarbons: Compounds containing only C and H atoms
- Unsaturation: Presence of double or triple C-C bonds
- Bromine Test: Decolorization indicates unsaturation
- Energy Changes: Exothermic reactions release more energy in bond formation than absorbed in bond breaking
Predicted Related Questions
- Write the equation for the incomplete combustion of ethyne
- Define the term “activation energy”
- Compare the reactivity of ethyne with ethene
Aqueous Ammonium Nitrite Decomposition
Aqueous ammonium nitrite decomposes when heated to form nitrogen:
(a) A 25.0 cm³ sample of 0.133 mol/dm³ NH₄NO₂ is completely decomposed. Calculate the volume of nitrogen formed, measured at room temperature and pressure. Give your answer to two significant figures.
(b) Describe and explain the effect of increasing the temperature on the rate of this reaction.
(c) Describe and explain the effect of decreasing the concentration of ammonium nitrite on the rate of this reaction.
(d) One way to measure the pH of aqueous ammonium nitrite is to use a pH meter. Describe one other way to measure the pH of aqueous ammonium nitrite.
Solutions
(a) 0.080 dm³
(b) The rate increases because particles have more kinetic energy, leading to more frequent and more energetic collisions.
(c) The rate decreases because there are fewer reactant particles per unit volume, leading to less frequent collisions.
(d) Using universal indicator paper and comparing the color to a chart.
Strategy & Concept
Calculation Strategy:
- Find moles of NH₄NO₂: Moles = Concentration × Volume (in dm³)
- Use mole ratio from equation to find moles of N₂ (1:1 ratio)
- Use molar volume (24 dm³/mol) to find volume of N₂
Rate of Reaction:
- Temperature: Increases kinetic energy and collision frequency
- Concentration: More particles per unit volume increases collision frequency
pH Measurement: Universal indicator provides a color-based pH estimation
Predicted Related Questions
- Calculate the volume of water produced in the same reaction
- Explain the effect of adding a catalyst on the rate of reaction
- Describe how to measure the rate of this reaction experimentally
Potassium Iodide Chemistry
Potassium iodide, KI, is an ionic solid composed of a lattice of potassium ions and iodide ions.
(a) Explain why potassium iodide has a high melting point.
(b) Describe how potassium atoms and iodine molecules react to form potassium ions and iodide ions. Use ideas about electron transfer.
(c) Predict the products at each electrode during the electrolysis of concentrated aqueous potassium iodide.
(d) Aqueous potassium iodide reacts with aqueous acidified potassium manganate(VII). Suggest the colour changes that happen during this reaction.
(e) The ionic equation for the reaction between aqueous potassium iodide and aqueous chlorine is shown. Explain, in terms of electrons, why this reaction involves both oxidation and reduction.
Solutions
(a) It has a giant ionic lattice with strong electrostatic forces between ions that require a lot of energy to break.
(b) Potassium atoms lose electrons to form K⁺ ions, iodine molecules gain electrons to form I⁻ ions.
(c) Anode: Iodine (I₂), Cathode: Hydrogen (H₂)
(d) Purple to colorless (and possibly brown from iodine formation).
(e) I⁻ ions lose electrons (oxidation), Cl₂ molecules gain electrons (reduction).
Strategy & Concept
Key Concepts:
- Ionic Bonding: Electron transfer from metal to non-metal
- Electrolysis: I⁻ oxidized at anode, H⁺ reduced at cathode (in aqueous solutions)
- Redox Reactions: Identify species that lose electrons (oxidation) and gain electrons (reduction)
- Color Changes: MnO₄⁻ (purple) reduced to Mn²⁺ (colorless), I⁻ oxidized to I₂ (brown)
Predicted Related Questions
- Write half-equations for the reactions at the electrodes in (c)
- State the observation when aqueous potassium iodide is added to aqueous lead(II) nitrate
- Explain why potassium iodide is soluble in water
Zinc Sulfite Equilibrium
When a sample of zinc sulfite is heated in a closed system, an equilibrium mixture is formed:
The forward reaction is endothermic.
(a) The temperature of the closed system is increased and the pressure is kept constant. Predict how the position of equilibrium of this reaction is affected. Explain your answer.
(b) The pressure of the closed system is decreased and the temperature is kept constant. Predict how the position of equilibrium of this reaction is affected. Explain your answer.
(c) Calculate the maximum mass of zinc oxide that can be made from 25.5 g of zinc sulfite.
(d) Zinc oxide reacts with both aqueous sodium hydroxide and dilute hydrochloric acid, but sulfur dioxide only reacts with aqueous sodium hydroxide. Explain why.
(e) Solid zinc sulfite reacts with dilute nitric acid to give sulfur dioxide gas, an aqueous zinc salt and a colourless liquid. Construct the symbol equation for this reaction. Include state symbols.
Solutions
(a) Shifts to the right. The forward reaction is endothermic, so it is favored by an increase in temperature.
(b) Shifts to the right. There are more gas molecules on the product side.
(c) 14.2 g
(d) ZnO is amphoteric, SO₂ is acidic.
(e) ZnSO₃(s) + 2HNO₃(aq) → Zn(NO₃)₂(aq) + SO₂(g) + H₂O(l)
Strategy & Concept
Le Chatelier’s Principle:
- Temperature: Increase favors endothermic direction
- Pressure: Decrease favors side with more gas molecules
Stoichiometry:
- Calculate moles of ZnSO₃
- Use 1:1 mole ratio to find moles of ZnO
- Calculate mass of ZnO
Oxide Properties:
- Amphoteric oxides react with both acids and bases
- Acidic oxides react only with bases
Predicted Related Questions
- Explain what happens to the equilibrium constant, Kc, when temperature is increased
- Calculate the volume of SO₂ gas produced in part (c)
- Describe a test to identify the gas produced in part (e)
Carbon Dioxide and Global Warming
Carbon dioxide is a greenhouse gas that is linked to increased global warming.
(a) Describe one adverse effect of increased global warming.
(b) Describe how carbon dioxide causes global warming.
(c) Photosynthesis removes carbon dioxide from the atmosphere.
(c)(i) Write the word equation for photosynthesis.
(c)(ii) Describe the conditions needed for photosynthesis.
(d) Explain one strategy to reduce global warming caused by carbon dioxide.
Solutions
(a) Rising sea levels / flooding of low-lying land.
(b) It allows short-wave radiation from the sun to pass through but absorbs the long-wave radiation re-emitted by the Earth, trapping heat.
(c)(i) carbon dioxide + water → glucose + oxygen
(c)(ii) Light and chlorophyll.
(d) Use renewable energy sources instead of burning fossil fuels.
Strategy & Concept
Greenhouse Effect:
- Short-wave radiation passes through atmosphere
- Earth re-radiates as long-wave (infrared) radiation
- Greenhouse gases absorb and re-radiate this heat
Photosynthesis:
- Process that converts CO₂ and water to glucose using light energy
- Requires chlorophyll as catalyst
Mitigation Strategies:
- Reduce fossil fuel consumption
- Increase use of renewable energy
- Carbon capture and storage
Predicted Related Questions
- Name another greenhouse gas
- Describe how deforestation contributes to increased global warming
- Explain how increased global warming affects biodiversity
Chlorine and Iodine Properties
Chlorine is a gas at room temperature. Iodine is a solid at room temperature.
(a) A sample of chlorine has a volume of 240 cm³ at room temperature and pressure. The pressure of the sample is increased at room temperature. Describe and explain, in terms of kinetic particle theory, what happens to the volume of the sample.
(b) When heated at atmospheric pressure, iodine changes directly into a gas without becoming a liquid. Describe the changes in particle separation, arrangement and motion during this change.
(c) At the same temperature and pressure, the rate of diffusion of chlorine gas is greater than that of iodine gas. Explain why.
(d) The symbol of an iodide ion is shown. Complete Table 7.1 about this iodide ion.
Solutions
(a) Volume decreases. The particles are forced closer together by the increased pressure.
(b) Separation: increases; Arrangement: from regular/ordered to random; Motion: from vibrating to moving randomly/rapidly.
(c) Chlorine molecules have a lower relative molecular mass.
(d) Electrons: 54; Neutrons: 75; Protons: 53
Strategy & Concept
Gas Laws:
- Boyle’s Law: Pressure increase at constant temperature decreases volume
- Particles forced closer together
Sublimation:
- Solid to gas transition
- Particle separation increases
- Arrangement becomes random
- Motion changes from vibration to rapid random movement
Diffusion:
- Graham’s Law: Lighter gases diffuse faster
- Chlorine (Cl₂, Mr=71) lighter than iodine (I₂, Mr=254)
Ion Structure:
- Protons = atomic number (53 for iodine)
- Neutrons = mass number – protons (128-53=75)
- Electrons = protons + charge (53+1=54 for I⁻)
Predicted Related Questions
- Describe the structure and bonding in solid iodine
- Explain why iodine has a higher melting point than chlorine
- Calculate the relative rate of diffusion of chlorine compared to iodine
Organic Chemistry Reactions
Fig. 8.1 is a flow diagram showing information about some organic chemical reactions.
(a) Compound A is one of the structural isomers of alcohols with molecular formula C₃H₈O.
(a)(i) State the name of compound A.
(a)(ii) Draw the displayed formula of the other structural isomer of C₃H₈O that is an alcohol.
(b) Draw the displayed formula of ester B.
(c) Draw the structural formula of propanoic acid.
(d) State the name and formula of compound D.
(e) State the name of gas E and of gas F.
(f) State the name of ester G.
Solutions
(a)(i) propan-1-ol
(a)(ii) Structure of propan-2-ol
(b) Structure of ethyl methanoate
(c) CH₃CH₂COOH
(d) name: magnesium propanoate, formula: (C₂H₅COO)₂Mg
(e) E: hydrogen, F: carbon dioxide
(f) ethyl propanoate
Strategy & Concept
Organic Reaction Pathways:
- Alcohols can be oxidized to carboxylic acids
- Carboxylic acids react with alcohols to form esters
- Carboxylic acids react with carbonates to produce CO₂
- Carboxylic acids react with metals to produce H₂
Isomerism:
- Structural isomers have same molecular formula but different structure
- C₃H₈O has two alcohol isomers: propan-1-ol and propan-2-ol
Ester Formation:
- Alcohol + carboxylic acid → ester + water
- Naming: alkyl from alcohol, alkanoate from acid
Predicted Related Questions
- State the reagent and conditions for converting A to propanoic acid
- Describe a test for gas E
- Explain the difference between structural and stereoisomers
Polymers and Plastics
Polymers are made by either an addition reaction or a condensation reaction.
(a) Describe the differences between addition and condensation polymerisation.
(b) PET is a condensation polymer. Name the type of linkage that bonds the repeat units to one another in PET.
(c) A polymer contains 47.1% carbon, 6.5% hydrogen and 46.4% chlorine by mass. Calculate the empirical formula of this polymer.
(d) Plastics are made from polymers. Describe two environmental challenges caused by plastics.
Solutions
(a) Addition uses unsaturated monomers / one product only. Condensation uses monomers with two functional groups / produces a small molecule (e.g., water) as a by-product.
(b) ester (linkage)
(c) C₃H₅Cl
(d) 1. They are non-biodegradable. 2. They cause harm to animals.
Strategy & Concept
Polymerization Types:
- Addition: Unsaturated monomers (C=C), only polymer formed
- Condensation: Monomers with functional groups, small molecule by-product (H₂O, HCl)
Empirical Formula Calculation:
- Assume 100g sample, find mass of each element
- Calculate moles of each element
- Find simplest whole number ratio
Environmental Issues:
- Non-biodegradable – persist in environment
- Harm to wildlife through ingestion/entanglement
- Microplastics in food chain
Predicted Related Questions
- Draw the structure of the monomer used to make poly(ethene)
- Suggest one way to reduce the environmental impact of plastics
- Explain why condensation polymers are biodegradable but addition polymers are not