Substance Identification
Choose from the following substances to answer the questions:
anhydrous copper(II) sulfate, calcium carbonate, carbon monoxide, chlorine, ethanoic acid, iron, 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 Contact process
(b) is a reducing agent in the blast furnace
(c) changes from a white solid to a blue solid when water is added to it
(d) kills microbes during the treatment of the domestic water supply
(e) has the empirical formula CH₂O
Solutions
(a) vanadium(V) oxide
(b) carbon monoxide
(c) anhydrous copper(II) sulfate
(d) chlorine
(e) methanoic acid
Strategy & Concept
This question tests your knowledge of specific chemical substances and their properties. You need to recall specific facts from the syllabus.
- Contact Process: Industrial production of sulfuric acid using vanadium(V) oxide catalyst
- Blast Furnace: Carbon monoxide reduces iron(III) oxide to iron
- Hydrated Salts: Anhydrous copper(II) sulfate is white, turns blue when hydrated
- Water Treatment: Chlorine is used to disinfect water by killing microbes
- Empirical Formula: Simplest whole-number ratio of atoms in a compound
Predicted Related Questions
- Name a substance that is an oxidizing agent in the blast furnace
- Identify a substance that is used as a catalyst in the Haber process
- Which substance is used to test for the presence of water?
Aluminium Carbide and Methane
Aluminium carbide, Al4C3, reacts with water to form methane, CH4, and aluminium hydroxide.
(a) Construct the symbol equation for this reaction.
(b) Methane is a saturated hydrocarbon.
(b)(i) Explain why methane is a hydrocarbon.
(b)(ii) Explain why methane is saturated.
(b)(iii) Methane reacts with chlorine in the presence of ultraviolet light. State the formulae of two products of this reaction.
(b)(iv) Draw a dot-and-cross diagram to show the electronic configuration in a molecule of methane.
(c) The equation for the complete combustion of methane is shown:
This reaction is exothermic.
(c)(i) Explain, using ideas about bond breaking and bond making, why this reaction is exothermic.
(c)(ii) Complete the reaction pathway diagram for the complete combustion of methane.
Reaction Pathway Diagram
Energy profile showing exothermic reaction
Drag the labels to the correct positions: Reactants, Products, ΔH, Ea
Solutions
(a) Al4C3 + 12H2O → 3CH4 + 4Al(OH)3
(b)(i) It contains only hydrogen and carbon atoms.
(b)(ii) It contains only single bonds between carbon atoms.
(b)(iii) CH3Cl and HCl
(b)(iv) Diagram showing C atom at center with four H atoms, each sharing one electron pair with carbon.
(c)(i) More energy is released forming the bonds in the products (CO2 and H2O) than is absorbed breaking the bonds in the reactants (CH4 and O2).
(c)(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
- Hydrocarbons: Compounds containing only C and H atoms
- Saturation: Presence of only single C-C bonds
- Substitution Reaction: Chlorine replaces hydrogen in methane
- 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 methane
- Explain why methane does not decolorize bromine water
- Describe the test for methane gas
Hydrogen Peroxide Decomposition
Aqueous hydrogen peroxide decomposes when heated to form oxygen:
(a) A 35.0 cm3 sample of 0.266 mol/dm3 H2O2 is completely decomposed. Calculate the volume of oxygen formed, measured at room temperature and pressure. Give your answer to two significant figures.
(b) Describe and explain the effect of decreasing the temperature on the rate of this reaction.
(c) Describe and explain the effect of increasing the concentration of hydrogen peroxide on the rate of this reaction.
(d) A sample of aqueous hydrogen peroxide has a pH of 5.5.
(d)(i) State which ion is responsible for this pH value.
(d)(ii) A pH meter is used to measure the pH of an aqueous solution. Describe one other way to measure the pH of an aqueous solution.
Solutions
(a) 0.11 dm3
(b) The rate decreases because particles have less kinetic energy, leading to less frequent and less energetic collisions.
(c) The rate increases because there are more reactant particles per unit volume, leading to more frequent collisions.
(d)(i) H+ ions
(d)(ii) Using universal indicator paper and comparing the color to a chart.
Strategy & Concept
Calculation Strategy:
- Find moles of H2O2: Moles = Concentration × Volume (in dm3)
- Use mole ratio from equation to find moles of O2 (2:1 ratio)
- Use molar volume (24 dm3/mol) to find volume of O2
Rate of Reaction:
- Temperature: Decreases 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 manganese(IV) oxide on the rate of this reaction
- Describe how to collect and test the gas produced in this reaction
Calcium Bromide Chemistry
Calcium bromide, CaBr2, is an ionic solid composed of a lattice of calcium ions and bromide ions.
(a) Explain why calcium bromide has a high melting point.
(b) Describe how calcium atoms and bromine molecules react to form calcium ions and bromide ions. Use ideas about electron transfer.
(c) Predict the products at each electrode during the electrolysis of dilute aqueous calcium bromide.
(d) (i) Ozone is an oxidising agent. Describe the colour change when ozone gas is bubbled through aqueous potassium iodide.
(d) (ii) Zinc is a reducing agent. Describe the colour change when excess zinc is added to acidified potassium manganate(VII).
(e) The ionic equation for the reaction between aqueous calcium bromide 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) Calcium atoms lose two electrons to form Ca2+ ions, bromine molecules gain electrons to form Br– ions.
(c) Anode: Oxygen (O2), Cathode: Hydrogen (H2)
(d)(i) Colorless to brown (due to formation of iodine)
(d)(ii) Purple to colorless
(e) Br– ions lose electrons (oxidation), Cl2 molecules gain electrons (reduction).
Strategy & Concept
Key Concepts:
- Ionic Bonding: Electron transfer from metal to non-metal
- Electrolysis: In dilute solutions, water molecules are preferentially discharged
- Redox Reactions: Identify species that lose electrons (oxidation) and gain electrons (reduction)
- Color Changes: Ozone oxidizes I– to I2 (brown), Zn reduces MnO4– (purple) to Mn2+ (colorless)
Predicted Related Questions
- Write half-equations for the reactions at the electrodes in (c)
- Explain why concentrated calcium bromide solution would give different products
- Describe a test to identify the gas produced at the cathode
Zinc Carbonate Equilibrium
When a sample of zinc carbonate is heated in a closed system, an equilibrium mixture is formed:
The forward reaction is endothermic.
(a) The temperature of the closed system is decreased 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 increased 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 4.23 g of zinc carbonate.
(d) Zinc oxide reacts with both aqueous sodium hydroxide and dilute hydrochloric acid, but carbon dioxide only reacts with aqueous sodium hydroxide. Explain why.
(e) Solid zinc carbonate reacts with dilute nitric acid to give a colourless solution and bubbles of a gas. Construct the symbol equation for this reaction. Include state symbols.
Solutions
(a) Shifts to the left. The forward reaction is endothermic, so it is favored by an increase in temperature. Decreasing temperature favors the exothermic reverse reaction.
(b) Shifts to the left. There are more gas molecules on the product side, so increasing pressure favors the side with fewer gas molecules.
(c) 2.73 g
(d) ZnO is amphoteric, CO2 is acidic.
(e) ZnCO3(s) + 2HNO3(aq) → Zn(NO3)2(aq) + CO2(g) + H2O(l)
Strategy & Concept
Le Chatelier’s Principle:
- Temperature: Decrease favors exothermic direction
- Pressure: Increase favors side with fewer gas molecules
Stoichiometry:
- Calculate moles of ZnCO3
- 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 would happen to the equilibrium if more CO2 is added
- Calculate the volume of CO2 gas produced in part (c)
- Describe a test to identify the gas produced in part (e)
Air Pollutants
Methane, nitrogen monoxide and sulfur dioxide are air pollutants.
(a) Describe one adverse effect of higher levels of methane in air.
(b) The combustion of fossil fuels that contain sulfur produces sulfur dioxide. Describe two strategies to reduce the emission of sulfur dioxide from the combustion of fossil fuels.
(c) Nitrogen monoxide, NO, is linked to acid rain.
(c)(i) This pollutant is present in the gases made in car engines. Describe how nitrogen monoxide is removed from these gases. Include a word equation in your answer.
(c)(ii) State two other adverse effects of oxides of nitrogen pollutants in the air.
Solutions
(a) Contributes to global warming / greenhouse effect
(b) 1. Use low-sulfur fuels; 2. Use flue gas desulfurization
(c)(i) Using catalytic converters; nitrogen monoxide + carbon monoxide → nitrogen + carbon dioxide
(c)(ii) 1. Respiratory problems; 2. Formation of photochemical smog
Oxygen and Sulfur Properties
Oxygen is a gas at room temperature. Sulfur is a solid at room temperature.
(a) A sample of oxygen has a volume of 540 cm³ at room temperature and pressure. The temperature of the sample is increased but the pressure is unchanged. Describe and explain, in terms of kinetic particle theory, what happens to the volume of the sample.
(b) Sulfur is a gas above 445 °C. Describe the changes in particle separation, arrangement and motion when a sample of sulfur gas is cooled down to room temperature.
(c) Describe diffusion in terms of kinetic particle theory.
(d) The symbol of a sulfide ion is shown. Complete Table 7.1 about this sulfide ion.
Solutions
(a) Volume increases. The particles gain kinetic energy and move faster, colliding with the container walls more frequently and forcefully.
(b) Separation: decreases; Arrangement: from random to regular/ordered; Motion: from moving randomly/rapidly to vibrating.
(c) The random movement of particles from an area of high concentration to an area of low concentration.
(d) Electrons: 18; Neutrons: 17; Protons: 16
Organic Chemistry Reactions
Fig. 8.1 is a flow diagram showing information about some organic chemical reactions.
(a) Draw the displayed formula of compound A.
(b) State the name of ester B.
(c) (i) State the name of compound C.
(c) (ii) Deduce the molecular formula of compound C.
(d) State the name and formula of compound D.
(e) State the formula of gas E and of liquid F.
(f) Draw the structural formula of ester G.
Solutions
(a) Structure of butan-1-ol: CH3-CH2-CH2-CH2OH
(b) ethyl ethanoate
(c)(i) butanoic acid
(c)(ii) C3H7COOH or C4H8O2
(d) name: sodium butanoate, formula: CH3CH2CH2COONa
(e) E: CO2, F: H2O
(f) CH3CH2COOCH2CH3
Polymers and Plastics
Polymers are made by either an addition reaction or a condensation reaction.
(a) Fig. 9.1 shows the equation for the reaction used to prepare a polymer. The monomer is both an alcohol and a carboxylic acid.
(a)(i) Name the type of linkage that bonds the repeat units to one another in this polymer.
(a)(ii) Explain how the equation shows that the polymer is made by a condensation reaction.
(b) A polymer contains 10.8% carbon, 17.1% fluorine and 72.1% bromine by mass. Calculate the empirical formula of this polymer.
(c) Some plastics are made from polymers that are hydrocarbons. There are many environmental challenges caused by plastics.
(c)(i) Explain why there is an accumulation of plastics in the oceans. Use ideas about the properties of plastics.
(c)(ii) Explain why the disposal of plastics causes an environmental challenge.
Solutions
(a)(i) ester linkage
(a)(ii) A small molecule (water) is produced as a by-product.
(b) C2F3Br3
(c)(i) Plastics are non-biodegradable and insoluble in water, so they accumulate.
(c)(ii) Plastics release toxic gases when burned and take up space in landfills.