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Question 1. What discovery has led to Dalton atomic model being modified? [1]

Question 2. Identify the element that has the electronic arrangement of its atoms shown in the image. [1]

Question 3. Define isotopes. [1]

Question 4. Complete the sentence: Elements are made up of small particles called _________. [1]

Question 5. What is brass made of? [1]

Question 6. Define filtration. [1]

Question 7. Thomas set up paper chromatography. He placed a drop of orange juice on a piece of card. Then, he put the card in a beaker with some water. Name the mobile phase in this experiment. [1]

Question 8. A black ink separated by using paper chromatography consists of an orange, red, blue, green and purple dyes with their retention factors in water being respectively 0.4, 0.87, 0.32, 0.98, 0.21. Which colour dye is the highest when the water reaches the top of paper? [1]

Question 9. What is the general name of elements X highlighted in the image? [1]

Question 10. Explain why iodine does not displace chlorine in sodium chloride that is dissolved in water. [1]

Question 11. Define a covalent structure. [2]

Question 12. Andres has drawn a dot and cross diagram for calcium oxide provided in the image. How should the diagram be corrected? [1]

Question 13. Isaac has collected some gas during an experiment and after he has passed it through lime water, the liquid became cloudy. Name the gas that Isaac has collected. [1]

Question 14. 2.2 mol of H₂SO₄ are mixed with 1.6 mol of KOH. How many moles of potassium sulphate are produced during the reaction between them?

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O [2]

Question 15. Explain why sodium metal does not displace iron in an iron chloride solution. [1]

Question 16. Provide an application for endothermic reactions. [1]

Question 17. Li has drawn a diagram that shows the bonds of both reactants and products of a reaction. Calculate the molar change of energy of the reaction by using the mean bond enthalpies provided below.

ΔH(H−H) = 436 kJ/mol
ΔH(O=O) = 495 kJ/mol
ΔH(N≡N) = 941 kJ/mol
ΔH(N−H) = 391 kJ/mol
ΔH(O−H) = 463 kJ/mol [2]

Question 18. Which of the following acids are weak?

phosphoric acid, hydrochloric acid, sulphuric acid, nitric acid, carbonic acid [2]

Question 19. Provide a balanced chemical equation for the reaction between butanoic acid and sodium oxide. [2]

Question 20. Alexander knows the concentrations of the solutions provided in the image. Describe how he can use them to produce a pure dry sample of NaCl. [2]

Question 21. Which test tube contains potassium ions? [1]

Question 22. Mary is performing a NaOH with HCl titration and she has chosen to use an indicator that is yellow in the base but red in the acid. Mary's setup just before she starts the titration is shown in the image and the colour of the liquid in the burette is red. What is wrong with the titration setup provided? [1]

Question 23. What is the volume of 1.73 mol/dm³ aluminium hydroxide solution needed to titrate 5.00 cm³ of 0.300 M sulphuric acid solution?

2Al(OH)₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 6H₂O [3]

Question 24. What is the volume of hydrogen gas needed to produce 50 mol of ammonia?

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) [2]

Question 25. What mass of hydrogen gas produces 340 g of ammonia?

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) [4]

Question 26. How many hydrogen atoms are there in 0.75 mol of NH₃? [2]

Question 27. Describe how the experimental set up in the image can be used to measure the rate of reaction between sodium thiosulfate and hydrochloric acid. [2]

Question 28. Name the barrier which molecules must overcome in order to react. [1]

Question 29. Name the state that is reached by a reversible chemical reaction in a closed system. [1]

Question 30. Determine atom economy for the production of NaOH according to 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g). [2]

Question 31. Explain why it can be challenging to use the flame test experiment to determine metal ions in a potassium chloride and sodium chloride mixture. [1]

Question 32. Provide a balanced chemical equation for the reaction between lithium and water. [2]

Question 33. Provide a definition for corrosion. [1]

Question 34. Provide a balanced chemical equation for the electrolysis of a molten compound shown in the image. [2]

Question 35. Which one of the following ions reaches the anode first during electrolysis?

SO₄²⁻, Cl⁻, Li⁺, H⁺, OH⁻, PO₄³⁻ [1]

Question 36. Two separate redox reactions within solutions can be linked with a salt bridge to create a cell. Explain the function of the salt bridge. [1]

Question 37. Finish and balance chemical equation CH₃CH₂OH + O₂ → ... [2]

Question 38. What are the most common uses for petrol? [2]

Question 39. Provide the molecular formula for pent-2-ene. [1]

Question 40. Predict the products of the oxidation of propan-1-ol. [2]

Question 41. Name the reaction presented in the image. [1]

Question 42. Taylor has got a solution of sodium iodide and they have decided to mix it with a silver nitrate solution and diluted nitric acid. What observation should they expect? [1]

Question 43. Cathleen has poured potassium hydroxide into a solution of some metal chloride. After mixing the solutions she has observed brown precipitate. Provide a chemical formula for the unknown compound. [1]

Question 44. Which of the following are the main sources of natural resources?

water, condensation, space, earth, manufacturing [1]

Question 45. Explain why paper is separated from plastic in recycling facilities. [1]

Question 46. Why is the second solution provided in the image more likely to be used to produce drinking water? [1]

Question 47. How did plants and algae influence the composition of the Earth's atmosphere since the planet's early days? [2]

Question 48. Describe the impact of particulates on human health. [1]

Question 49. Define the greenhouse effect. [1]

Question 50. Discuss how a worldwide interruption in ammonia production could affect a potato harvest. [2]

Question 51. What was the discovery made by Ernest Rutherford using alpha particle scattering experiment? [1]

Question 52. One of hydrogen isotopes has 1 proton in each of its atoms. How many protons does a twice heavier hydrogen isotope atom have? [1]

Question 53. 75% of naturally existing chlorine atoms are ³⁵Cl and 25% are ³⁷Cl. Calculate the relative atomic mass of chlorine to one decimal place. [2]

Question 54. Which one of the following elements is the most likely to have chemical properties similar to calcium?

rubidium, strontium, yttrium, zirconium, niobium [1]

Question 55. Provide a reason why gas particles can be at longer distances to each other in comparison to liquid particles. [1]

Question 56. Define simple distillation. [1]

Question 57. Provide a definition for chromatography. [1]

Question 58. Braden performed a paper chromatography experiment. He placed a water-based ink on a horizontal pencil line. The die rose to the same level as the top of the solvent. What is the retention factor of the substance? [1]

Question 59. Define metallic bonding. [3]

Question 60. Provide a balanced chemical equation for the reaction that happens when chlorine is added to a calcium iodide solution. [1]

Question 61. Explain why most materials with a covalent network structure do not conduct electricity. [1]

Question 62. Explain why nitrogen has a relatively low melting point. [2]

Question 63. Describe the test for identifying oxygen gas. [1]

Question 64. Determine the limiting reactant in the reaction between 50 g of sulphur and 60 g of aluminium. Show your working.

2Al + 3S → Al₂S₃ [3]

Question 65. Provide a balanced chemical equation for the reaction in the beaker. [2]

Question 66. Name A and B shown in the reaction profile. [1]

Question 67. How many bonds are broken during the reaction provided?

CH₄ + 2O₂ → CO₂ + 2H₂O [1]

Question 68. The concentration of an alkaline solution has been reduced by 1000 times by diluting it. Find the pH of the newly created solution if the pH of the initial solution is 12. [1]

Question 69. What is a balanced equation for the reaction of butanoic acid with strontium oxide? [2]

Question 70. Provide the steps on how to produce soluble salts without using titration, starting with an acid and an insoluble metal hydroxide. [3]

Question 71. Define ionic bonding. [1]

Question 72. Name the 3 pieces of chemical equipment provided in the same order they are presented in the image. [3]

Question 73. 4 moles of sodium hydroxide have been neutralised with sulphuric acid. Use the balanced equation provided to find the amount of sulphuric acid that has reacted with the base.

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O [1]

Question 74. Find the volume that 5.0 mol of methane gas takes at room temperature and pressure. [1]

Question 75. Calculate the mass of ammonia gas needed to produce 107 g of ammonium chloride?

NH₃(g) + HCl(g) → NH₄Cl(s) [3]

Question 76. Sophie has 5.4 mol of AgNO₃ available in the lab. What is the maximum volume of 3.0 mol/dm³ silver nitrate solution that she can make? [1]

Question 77. How can the rate of reaction between calcium carbonate chips and hydrochloric acid be determined? [2]

Question 78. Which one of the curves provided represents a reaction carried out at the lowest temperature? [1]

Question 79. Provide the symbol that is used to represent a reaction that can reach equilibrium. [1]

Question 80. Calculate atom economy for the production of iron according to the reaction equation provided.

Fe₃O₄(s) + 2C(s) → 3Fe(s) + 2CO₂(g) [2]

Question 81. What colour does lithium produce during a flame test? [1]

Question 82. Identify all particles that are reduced in the half-equations provided.

2Cl⁻ → Cl₂ + 2e⁻
Mn⁵⁺ + 3e⁻ → Mn²⁺ [1]

Question 83. Name the substance that iron needs to rust apart from water. [1]

Question 84. Provide a chemical equation for the electrolysis of copper(II) chloride. [1]

Question 85. What are the formulae of ions participating in oxidation and reduction reactions at relevant electrodes during the electrolysis of potassium bromide solution? [2]

Question 86. Name two main factors that affect the voltage created by a chemical cell. [2]

Question 87. Balance equation CH₃OH + O₂ → CO₂ + H₂O. [1]

Question 88. Name three fractions of crude oil. [3]

Question 89. Gareth reacted substance X with but-2-ene to produce C₄H₉Cl. Name X. [1]

Question 90. Discuss how a reduction in national grape yield in California can affect local ethanol prices. [3]

Question 91. Miko drew a polymer structure provided in the image. What needs adding to his diagram? [1]

Question 92. Name the compound that is commonly used to test for bromide ions in a solution. [1]

Question 93. What colour precipitate does mixing a NaOH solution with a CuCl₂ solution form? [1]

Question 94. Compare the biodegradability of paper and plastic. [1]

Question 95. Which of the following materials can be recycled by crushing and melting to produce granules?

glass, wood, paper, metal, concrete, plastic [1]

Question 96. Describe how a coastal city without rivers or underground water might obtain drinking water. [2]

Question 97. Over time sediments have absorbed large amounts of carbon dioxide. Name two examples of such deposits. [2]

Question 98. Describe the effects of sulphur dioxide on human health. [1]

Question 99. Describe the impact of burning fossil fuels on climate. [2]

Question 100. Name the compound essential in the production of ammonium salts. [1]

Answer 1. What discovery has led to Dalton atomic model being modified? [1]

Dalton atomic model has been disproven when negative particles electrons were discovered by Joseph John Thompson leading to a new plum pudding atomic model.

discovery of an electron

Answer 2. Identify the element that has the electronic arrangement of its atoms shown in the image. [1]

The atomic number of an element is the sum of the numbers in the electronic configuration; 2 + 8 + 3 = 13. The element that has 13 electrons is aluminium.

aluminium

Answer 3. Define isotopes. [1]

Isotopes of an element are atoms with the same number of protons but a different number of neutrons or, alternatively, atoms with the same atomic number but a different mass number.

atoms with same number of protons, different numbers of neutrons

Answer 4. Complete the sentence: Elements are made up of small particles called _________. [1]

Elements are made up of small particles called atoms.

atoms

Answer 5. What is brass made of? [1]

Brass is a copper and zinc alloy that has a relatively low melting point allowing it to be used for the production of musical instruments and taps.

copper, zinc

Answer 6. Define filtration. [1]

Filtration is a physical process during which insoluble substance is removed from a liquid.

separation of insoluble substance from a liquid

Answer 7. Thomas set up paper chromatography. He placed a drop of orange juice on a piece of card. Then, he put the card in a beaker with some water. Name the mobile phase in this experiment. [1]

Paper chromatography uses a piece of card (stationary phase) with a horizontal line drawn on it using a pencil and a drop of a mixture put on the line. The bottom of the card is then submerged into a suitable solvent (mobile phase) below the line and solvent rises up the card. Since the solvent used is water, it is also the mobile phase.

water

Answer 8. A black ink separated by using paper chromatography consists of an orange, red, blue, green and purple dyes with their retention factors in water being respectively 0.4, 0.87, 0.32, 0.98, 0.21. Which colour dye is the highest when the water reaches the top of paper? [1]

Retention factor is a measure of a fractional length a compound travels on a stationary phase. Since the green dye has the highest retention factor, it is going to reach the highest position.

green

Answer 9. What is the general name of elements X highlighted in the image? [1]

Transition metals are found in groups 1B to 10B or 2 to 12.

transition metals

Answer 10. Explain why iodine does not displace chlorine in sodium chloride that is dissolved in water. [1]

A more reactive halogen displaces a less reactive halogen in halide salt solutions. The reactivity of halogens decreases going down the group 7 of the periodic table. Since iodine is lower down the group 7 than chlorine, it it is less reactive and does not displace chlorine in its salt.

Iodine is less reactive than chlorine.

Answer 11. Define a covalent structure. [2]

A covalent (network) structure is a large lattice consisting of atoms connected with covalent bonds

[1 mark] large lattice of atoms
[1 mark] bonded with covalent bonds

Answer 12. Andres has drawn a dot and cross diagram for calcium oxide provided in the image. How should the diagram be corrected? [1]

Usually dots are used to represent electrons originating from one element and crosses are used for the electrons that come from the other element. Since 2 of the 8 electrons surrounding oxide ion are from calcium, they should be represented using different symbols, for example, crosses.

2 of the dots should be crosses instead.

Answer 13. Isaac has collected some gas during an experiment and after he has passed it through lime water, the liquid became cloudy. Name the gas that Isaac has collected. [1]

Carbon dioxide can be identified by passing it through lime water which is a clear solution of calcium hydroxide. If a gas contains CO₂, lime water becomes cloudy.

carbon dioxide

Answer 14. 2.2 mol of H₂SO₄ are mixed with 1.6 mol of KOH. How many moles of potassium sulphate are produced during the reaction between them?

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O [2]

In order to determine which reactant is the limiting reactant, divide the amount in moles of each substance by its coefficient in the chemical equation and the reactant that has the lowest result is the limiting one.

n(H₂SO₄) ÷ N(H₂SO₄) = 2.2 ÷ 1 = 2.2 mol
n(KOH) ÷ N(KOH) = 1.6 ÷ 2 = 0.80 mol
0.80 mol < 2.2 mol, KOH is the limiting reactant.

N(KOH) : N(K₂SO₄) = 2 : 1
n(K₂SO₄) × N(KOH) = n(KOH) × N(K₂SO₄)
n(K₂SO₄) × 2 = 1.6 × 1
n(K₂SO₄) = 0.80 mol

[2 marks] 0.8 mol or 0.80 mol
[1 mark only] 0.80 or 0.8
[1 mark only] limiting reactant: KOH

Answer 15. Explain why sodium metal does not displace iron in an iron chloride solution. [1]

A more reactive metal displaces a less reactive metal in its salt solution unless the more reactive metal reacts with water in a solution. Since sodium reacts vigorously with water, sodium does not displace iron in an iron chloride solution.

sodium reacting with water in solution

Answer 16. Provide an application for endothermic reactions. [1]

Endothermic reactions can be useful for cooling down injuries.

cold packs

Answer 17. Li has drawn a diagram that shows the bonds of both reactants and products of a reaction. Calculate the molar change of energy of the reaction by using the mean bond enthalpies provided below.

ΔH(H−H) = 436 kJ/mol
ΔH(O=O) = 495 kJ/mol
ΔH(N≡N) = 941 kJ/mol
ΔH(N−H) = 391 kJ/mol
ΔH(O−H) = 463 kJ/mol [2]

The energy transferred in a chemical reaction can be calculated by subtracting total bond enthalpies of products from the total bond enthalpies of reactants. If multiple same bonds are broken or formed, multiples of the bond energies are used.

In this case two H−H, one O=O bonds are broken and four O−H bonds are made.
ΔH = 436 × 2 + 495 − 463 × 4
ΔH = 872 + 495 − 1852
ΔH = −485 kJ/mol

[2 marks] −485 kJ/mol
[1 mark] (−)485 or 1367 or 1852 or 436 × 2 + 495 − 463 × 4

Answer 18. Which of the following acids are weak?

phosphoric acid, hydrochloric acid, sulphuric acid, nitric acid, carbonic acid [2]

Examples of strong acids include hydrochloric acid (HCl), sulphuric acid (H₂SO₄), and nitric acid (HNO₃). Examples of weak acids include carbonic acid (H₂CO₃), phosphoric acid (H₃PO₄), and many organic acids.

[1 mark] phosphoric acid
[1 mark] carbonic acid

Answer 19. Provide a balanced chemical equation for the reaction between butanoic acid and sodium oxide. [2]

Carboxylic acids react with some metal oxides and metal hydroxides to produce a salt and water.

[2 marks] Na₂O + 2CH₃CH₂CH₂COOH → 2CH₃CH₂CH₂COONa + H₂O
[1 mark] correct equation without coefficients

Answer 20. Alexander knows the concentrations of the solutions provided in the image. Describe how he can use them to produce a pure dry sample of NaCl. [2]

Both HCl and NaOH are soluble in water. Therefore, he can prepare a soluble salt by titration by reacting the acid with a soluble metal hydroxide. Titration ensures that exact amounts of each compound are mixed since soluble metal hydroxides cannot be removed from a solution by filtration. After he obtains the salt solution using titration, he could use evaporation to crystallise the salt.

[1 mark] titration
[1 mark] crystallisation/evaporation

Answer 21. Which test tube contains potassium ions? [1]

Test tube B should have potassium ions since the formula displayed nearby has K in it which stands for potassium.

B

Answer 22. Mary is performing a NaOH with HCl titration and she has chosen to use an indicator that is yellow in the base but red in the acid. Mary's setup just before she starts the titration is shown in the image and the colour of the liquid in the burette is red. What is wrong with the titration setup provided? [1]

One of the solutions during a titration is placed into a conical flask with a few drops of an indicator. The flask is placed directly below the burette to avoid spillages and the titrant is slowly poured to the conical flask while stirring it. When the indicator changes the colour to signify the end of the reaction, the volume of the titrant used is recorded.

The indicator has been put in the burette.

Answer 23. What is the volume of 1.73 mol/dm³ aluminium hydroxide solution needed to titrate 5.00 cm³ of 0.300 M sulphuric acid solution?

2Al(OH)₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 6H₂O [3]

n(H₂SO₄) = c(H₂SO₄) × V(H₂SO₄) = 0.300 × 0.00500 = 1.50 × 10⁻³ mol

N(Al(OH)₃) : N(H₂SO₄) = 2 : 3
N₁n₂ = N₂n₁
N(Al(OH)₃) × n(H₂SO₄) = N(H₂SO₄) × n(Al(OH)₃)
2 × 1.50 × 10⁻³ = 3 × n(Al(OH)₃)
n(Al(OH)₃) = 2 × 1.50 × 10⁻³ ÷ 3 = 1.00 × 10⁻³ mol

c(Al(OH)₃) = n(Al(OH)₃) ÷ V(Al(OH)₃)
1.73 = 1.00 × 10⁻³ ÷ V(Al(OH)₃)
V(Al(OH)₃) = 1.00 × 10⁻³ ÷ 1.73 = 5.78 × 10⁻⁴ dm³

[3 marks] 5.78 × 10⁻⁴ dm³
[2 marks only] 5.78 × 10⁻⁴ or 1.00 × 10⁻³
[1 mark] 1.50 × 10⁻³

Answer 24. What is the volume of hydrogen gas needed to produce 50 mol of ammonia?

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) [2]

N(H₂) : N(NH₃) = 3 : 2
n(H₂) × N(NH₃) = n(NH₃) × N(H₂)
n(H₂) × 2 = 50 × 3
n(H₂) = 75 mol
V(H₂) = 75 × 24 = 1800 dm³

[2 marks] 1800 dm³
[1 mark] 1800 or 75

Answer 25. What mass of hydrogen gas produces 340 g of ammonia?

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) [4]

M(NH₃) = 17 g/mol
n(NH₃) = 340 ÷ 17 = 20 mol
N(H₂) : N(NH₃) = 3 : 2
n(H₂) × N(NH₃) = n(NH₃) × N(H₂)
n(H₂) × 2 = 20 × 3
n(H₂) = 30 mol
m(H₂) = 30 × 2 = 60 g

[4 marks] 60 g
[3 marks only] 60 or 30
[2 marks only] 20
[1 mark] 17

Answer 26. How many hydrogen atoms are there in 0.75 mol of NH₃? [2]

There are three hydrogen atoms in each NH₃ molecule.
N = 3 × n × A
N = 3 × 0.75 × 6.02 × 10²³ = 1.4 × 10²⁴ (2 s. f.)

[2 marks] 1.4 × 10²⁴
[1 mark] 4.5 × 10²³ or 2.25

Answer 27. Describe how the experimental set up in the image can be used to measure the rate of reaction between sodium thiosulfate and hydrochloric acid. [2]

When sodium thiosulfate and hydrochloric acid are mixed, the solution goes from clear to cloudy as a precipitate forms. To measure the rate of this reaction, we place a conical flask with sodium thiosulfate over a piece of paper with a cross drawn on it. The cross should be visible through the clear solution. When we add hydrochloric acid, the solution turns cloudy. We measure the time taken for the cross to disappear - this measures the reaction rate.

[1 mark] Mix sodium thiosulphate and hydrochloric acid.
[1 mark] Measure the time taken for the cross to disappear.

Answer 28. Name the barrier which molecules must overcome in order to react. [1]

The energy that molecules must possess in order to react is known as the activation energy.

activation energy

Answer 29. Name the state that is reached by a reversible chemical reaction in a closed system. [1]

In a closed system, i.e. a system where matter cannot enter or leave the system, the reaction can reach what is known as a dynamic equilibrium.

dynamic equilibrium

Answer 30. Determine atom economy for the production of NaOH according to 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g). [2]

M(Na) = 23 g/mol
M(H₂O) = 18 g/mol
M(NaOH) = 40 g/mol

e = 40 × 2 / (23 × 2 + 18 × 2) × 100%
e = 80 / 82 × 100%
e = 98%

[2 marks] 98%
[1 mark] 23 and 18 and 40

Answer 31. Explain why it can be challenging to use the flame test experiment to determine metal ions in a potassium chloride and sodium chloride mixture. [1]

When multiple ions are present in a sample, their colours can mix during a flame test and make it difficult to determine the ions.

several colours mixing

Answer 32. Provide a balanced chemical equation for the reaction between lithium and water. [2]

The most reactive metals react with water to produce metal hydroxides and hydrogen.

[2 marks] 2Li + 2H₂O → 2LiOH + H₂
[1 mark] correct unbalanced equation

Answer 33. Provide a definition for corrosion. [1]

Corrosion is a process during which substances are damaged by reacting with chemicals in the environment.

damage of substances by chemicals in the environment

Answer 34. Provide a balanced chemical equation for the electrolysis of a molten compound shown in the image. [2]

During many of the electrolysis reactions, pure elements are produced. Since sodium chloride contains sodium and chloride elements, sodium metal and chloride gas are produced during this reaction.

[2 marks] 2NaCl → 2Na + Cl₂
[1 mark] correct unbalanced equation

Answer 35. Which one of the following ions reaches the anode first during electrolysis?

SO₄²⁻, Cl⁻, Li⁺, H⁺, OH⁻, PO₄³⁻ [1]

In aqueous solutions, chloride ions (Cl⁻) are usually discharged at the anode before sulfate ions (SO₄²⁻) or other larger anions because chloride ions have a lower discharge potential compared to sulfate and other complex anions. Hydroxide ions (OH⁻) could also be discharged if they are present in high enough concentration, as they can compete with chloride ions for discharge.

Cl⁻

Answer 36. Two separate redox reactions within solutions can be linked with a salt bridge to create a cell. Explain the function of the salt bridge. [1]

The salt bridge completes the circuit by providing relevant ions to the solution it connects.

completing the circuit by providing ions

Answer 37. Finish and balance chemical equation CH₃CH₂OH + O₂ → ... [2]

The first step is to write the unbalanced chemical equation for the reaction: CH₃CH₂OH + O₂ → CO₂ + H₂O. Next, we need to balance the equation so that there are equal numbers of atoms of each kind on each side of the equation. In this case, we need to add a coefficient of 3 to the water molecule and 2 to the carbon dioxide molecule on the right side: CH₃CH₂OH + O₂ → 2CO₂ + 3H₂O. Finally, we need to add a coefficient of 3 to the oxygen molecule on the left side: CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O.

[2 marks] CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O
[1 mark] correct unbalanced equation

Answer 38. What are the most common uses for petrol? [2]

Petrol is fuel for cars and power equipment.

[1 mark] transport
[1 mark] power equipment

Answer 39. Provide the molecular formula for pent-2-ene. [1]

The molecular formula for pent-2-ene is C₅H₁₀.

C₅H₁₀

Answer 40. Predict the products of the oxidation of propan-1-ol. [2]

The predicted products of propan-1-ol (C₃H₇OH) oxidation are propanoic acid (C₃H₆O₂) and water.

[1 mark] propanoic acid
[1 mark] water

Answer 41. Name the reaction presented in the image. [1]

The reaction presented in the image is called addition polymerisation, the process of forming an addition polymer from monomers by bonding together through a chemical bond with no other by-products.

addition polymerisation

Answer 42. Taylor has got a solution of sodium iodide and they have decided to mix it with a silver nitrate solution and diluted nitric acid. What observation should they expect? [1]

Halide ions can be identified by adding silver nitrate with diluted nitric acid to their solutions. Presence of iodide results in yellow AgI precipitate.

yellow precipitate

Answer 43. Cathleen has poured potassium hydroxide into a solution of some metal chloride. After mixing the solutions she has observed brown precipitate. Provide a chemical formula for the unknown compound. [1]

In the presence of Fe³⁺ ions NaOH forms brown precipitate.

FeCl₃

Answer 44. Which of the following are the main sources of natural resources?

water, condensation, space, earth, manufacturing [1]

The main sources of natural resources are the earth (such as minerals and fossil fuels), water, plants, and animals.

water, earth

Answer 45. Explain why paper is separated from plastic in recycling facilities. [1]

Paper and plastic are separated in recycling facilities because they are recycled differently. Paper is typically recycled by pulping and repulping, while plastic is recycled by melting and reforming. Separating paper and plastic allows the materials to be processed more efficiently and effectively.

They are recycled differently.

Answer 46. Why is the second solution provided in the image more likely to be used to produce drinking water? [1]

In some areas only sea water is available which needs to be desalinated before it becomes potable. Desalination is an energy consuming process that can be performed using distillation or reverse osmosis making it expensive to provide drinking water via this route. However, required salts could much more easily added to the distilled water to make it potable.

Adding salt to pure water is less expensive than desalination.

Answer 47. How did plants and algae influence the composition of the Earth's atmosphere since the planet's early days? [2]

Since the planet's early days, plants and algae have influenced the composition of the Earth's atmosphere by producing oxygen through photosynthesis. This process releases large amounts of oxygen into the atmosphere, which is essential for the survival of most living organisms.

[1 mark] oxygen production via photosynthesis
[1 mark] carbon dioxide consumption via photosynthesis

Answer 48. Describe the impact of particulates on human health. [1]

Particulates are tiny particles that can be inhaled into the lungs and cause respiratory problems. Inhaling particulates can irritate the eyes, nose, throat, and lungs and aggravate respiratory conditions such as asthma. Long-term exposure to high levels of particulates can lead to chronic bronchitis and reduced lung function.

respiratory problems

Answer 49. Define the greenhouse effect. [1]

The greenhouse effect is heat retention by some gases in the Earth's atmosphere.

heat retention by gases in the atmosphere

Answer 50. Discuss how a worldwide interruption in ammonia production could affect a potato harvest. [2]

A worldwide interruption in ammonia production could affect the potato harvest. We use ammonia to produce fertilisers, which are critical for agriculture. Without fertilisers, the growth and yield of the crop might drop, leading to a shortage of potatoes.

[1 mark] less fertilisers
[1 mark] lower yield

Answer 51. What was the discovery made by Ernest Rutherford using alpha particle scattering experiment? [1]

Soon after the discovery of electrons, alpha scattering experiment has been performed by Ernest Rutherford that has suggested the existence of a nucleus at the centre of an atom.

nucleus of an atom

Answer 52. One of hydrogen isotopes has 1 proton in each of its atoms. How many protons does a twice heavier hydrogen isotope atom have? [1]

Each element has its specific atomic number that is the same as the number of protons in an atom of the element. Since both of the mentioned atoms are of hydrogen element, they both have 1 proton in each of their atoms.

1

Answer 53. 75% of naturally existing chlorine atoms are ³⁵Cl and 25% are ³⁷Cl. Calculate the relative atomic mass of chlorine to one decimal place. [2]

Relative atomic mass is found by multiplying atomic mass by the abundance for each isotope, adding the results and dividing the sum by the sum of abundances.

M = (75% × 35 + 25% × 37) ÷ (25% + 75%)
M = (2625 + 925) ÷ 100
M = 35.5 g/mol

[2 marks] 35.5 g/mol
[1 mark] 35.5 or (2625 + 925) ÷ 100

Answer 54. Which one of the following elements is the most likely to have chemical properties similar to calcium?

rubidium, strontium, yttrium, zirconium, niobium [1]

Many elements in the same groups have similar physical and chemical properties due to having the same number of electrons in their outer shells. The only element from the ones provided that is in the same group as calcium is strontium.

strontium

Answer 55. Provide a reason why gas particles can be at longer distances to each other in comparison to liquid particles. [1]

Gas particles have more energy and are able to move around at large distances to other particles.

Gas particles have more energy.

Answer 56. Define simple distillation. [1]

Distillation is a physical technique used to separate liquids with different boiling points.

separation of liquids with different boiling points

Answer 57. Provide a definition for chromatography. [1]

Chromatography is a separation of compounds dissolved in a solvent.

separation of compounds dissolved in a solvent

Answer 58. Braden performed a paper chromatography experiment. He placed a water-based ink on a horizontal pencil line. The die rose to the same level as the top of the solvent. What is the retention factor of the substance? [1]

The retention factor is the ratio of a substance's distance and the solvent's distance. If they are both the same, this ratio is 1.

1

Answer 59. Define metallic bonding. [3]

Metallic bonding is the electrostatic attraction between metal ions and delocalised electrons they share.

[1 mark] electrostatic attraction
[1 mark] metal ions
[1 mark] delocalised electrons

Answer 60. Provide a balanced chemical equation for the reaction that happens when chlorine is added to a calcium iodide solution. [1]

A more reactive halogen displaces a less reactive halogen in halide salt solutions. Chlorine is more reactive than iodine, thus chlorine displaces iodine in the salt.

CaI₂ + Cl₂ → CaCl₂ + I₂

Answer 61. Explain why most materials with a covalent network structure do not conduct electricity. [1]

Most giant covalent structures like diamond, silica or silicon do not have charged particles that are free to move to transfer the charge. Thus, they do not conduct electricity, even when molten.

no free-to-move charged particles

Answer 62. Explain why nitrogen has a relatively low melting point. [2]

Nitrogen exists as N₂ molecules that have weak intermolecular forces. The weak interactions result in nitrogen having a low melting point as weak intermolecular forces are broken instead of strong covalent bonds when melting.

[1 mark] weak intermolecular forces
[1 mark] requiring little energy to break

Answer 63. Describe the test for identifying oxygen gas. [1]

The test for oxygen involves bringing a splint into contact with the gas. A glowing splint relights in oxygen.

glowing splint relighting

Answer 64. Determine the limiting reactant in the reaction between 50 g of sulphur and 60 g of aluminium. Show your working.

2Al + 3S → Al₂S₃ [3]

In order to determine which reactant is the limiting reactant, divide the amount in moles of each substance by its coefficient in the chemical equation, and the reactant with the lowest result is the limiting one.

n(Al) = 60 ÷ 27 = 2.2 mol
n(S) = 50 ÷ 32 = 1.6 mol

n(Al) ÷ N(Al) = 2.2 ÷ 2 = 1.1 mol
n(S) ÷ N(S) = 1.6 ÷ 3 = 0.53 mol
0.53 mol < 1.1 mol

[1 mark] sulphur
[1 mark] 0.53 and 1.1
[1 mark] 2.2 and 1.6

Answer 65. Provide a balanced chemical equation for the reaction in the beaker. [2]

A more reactive metal displaces a less reactive metal in its salt solution, unless the more reactive metal reacts with water.

[2 marks] 2Al + 3FeCl₂ → 2AlCl₃ + 3Fe
[1 mark] correct unbalanced equation

Answer 66. Name A and B shown in the reaction profile. [1]

Reaction profile shows the energies of reactants, intermediates and products in a reaction.

A = reactants, B = products

Answer 67. How many bonds are broken during the reaction provided?

CH₄ + 2O₂ → CO₂ + 2H₂O [1]

CH₄ has 4 C−H bonds and 2O₂ has 2 O=O bonds; in total 4 + 2 = 6.

6

Answer 68. The concentration of an alkaline solution has been reduced by 1000 times by diluting it. Find the pH of the newly created solution if the pH of the initial solution is 12. [1]

Diluting an alkaline solution usually results in a pH value decreasing as it becomes more neutral. Changing the concentration of H⁺ or OH⁻ ions in a solution by 10 times is equivalent to changing the pH by 1 unit.

Since the alkaline solution has been diluted, its pH has decreased. The concentration has been decreased by 1000 times; therefore, the pH has to change by 3. Combined together these statements result in the pH changing from 12 to 9.

9

Answer 69. What is a balanced equation for the reaction of butanoic acid with strontium oxide? [2]

Carboxylic acids react with some metal oxides and metal hydroxides to produce a salt and water.

[2 marks] SrO + 2CH₃CH₂CH₂COOH → (CH₃CH₂CH₂COO)₂Sr + H₂O
[1 mark] correct unbalanced equation

Answer 70. Provide the steps on how to produce soluble salts without using titration, starting with an acid and an insoluble metal hydroxide. [3]

Pure soluble salts are usually produced by reacting an acid with an excess of insoluble metal hydroxide. This ensures that no acid is left once the reaction is finished, but the insoluble metal hydroxide is removed using filtration. The filtrate is then evaporated to produce crystals of the soluble salt.

[1 mark] acid + excess of metal hydroxide
[1 mark] filtrating metal hydroxide out
[1 mark] evaporating filtrate

Answer 71. Define ionic bonding. [1]

Ionic bonding is an electrostatic attraction between oppositely charged ions.

electrostatic attraction between oppositely charged ions

Answer 72. Name the 3 pieces of chemical equipment provided in the same order they are presented in the image. [3]

Volumetric flask is usually taller than the conical flask. Burette is long and has a stopcock at the end of it. Conical flask has a cone shape.

[1 mark] volumetric flask
[1 mark] burette
[1 mark] conical flask

Answer 73. 4 moles of sodium hydroxide have been neutralised with sulphuric acid. Use the balanced equation provided to find the amount of sulphuric acid that has reacted with the base.

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O [1]

N(NaOH) : N(H₂SO₄) = 2 : 1
N₁n₂ = N₂n₁
N(NaOH) × n(H₂SO₄) = N(H₂SO₄) × n(NaOH)
2 × n(H₂SO₄) = 1 × 4
n(H₂SO₄) = 4 ÷ 2 = 2 mol

2 mol

Answer 74. Find the volume that 5.0 mol of methane gas takes at room temperature and pressure. [1]

V = n × v
V = 5.0 × 24 = 120 dm³

120 dm³

Answer 75. Calculate the mass of ammonia gas needed to produce 107 g of ammonium chloride?

NH₃(g) + HCl(g) → NH₄Cl(s) [3]

M(NH₄Cl) = 53.5 g/mol
n(NH₄Cl) = 107 ÷ 53.5 = 2.00 mol
N(NH₃) : N(NH₄Cl) = 1 : 1
The same amount of moles of NH₃ are required.
m(NH₃) = 2.00 × 17 = 34 g

[3 marks] 34 g
[1 mark] 34 or 1 : 1
[1 mark] 2(...) or 53.5

Answer 76. Sophie has 5.4 mol of AgNO₃ available in the lab. What is the maximum volume of 3.0 mol/dm³ silver nitrate solution that she can make? [1]

c = m ÷ V
3.0 = 5.4 ÷ V
V = 5.4 ÷ 3.0 = 1.8 dm³

1.8 dm³

Answer 77. How can the rate of reaction between calcium carbonate chips and hydrochloric acid be determined? [2]

To measure the rate of reaction when calcium carbonate chips are added to hydrochloric acid to produce carbon dioxide gas, the following protocol could be used. The reactants are added to a conical flask with cotton wool at the top which allows the gas formed to leave the flask. As the reaction proceeds, measure the mass of the flask containing the reactants. The mass should decrease as time goes on. The decrease in mass over time is a measure of the rate. Alternatively, the volume of gas produced over time could be measured using a syringe. The increase in volume over time is a measure of the rate of reaction

[1 mark] Add reactants to a flask with cotton wool.
[1 mark] Measure the decrease in mass over time.
[1 mark] Add reactants to a flask connected to a syringe.
[1 mark] Measure the volume of gas produced over time.

Answer 78. Which one of the curves provided represents a reaction carried out at the lowest temperature? [1]

At a lower temperature, the rate of reaction is decreased. This means that the curve of mass of the product against time will have a less steep gradient. The curve indicated by D has the least steep gradient and therefore represents the reaction being carried out at a lower temperature than other.

D

Answer 79. Provide the symbol that is used to represent a reaction that can reach equilibrium. [1]

Reversible reactions are indicated in the equation using this arrow: ⇌.

⇌

Answer 80. Calculate atom economy for the production of iron according to the reaction equation provided.

Fe₃O₄(s) + 2C(s) → 3Fe(s) + 2CO₂(g) [2]

M(Fe₃O₄) = 231.7 g/mol
M(C) = 12 g/mol
M(Fe) = 55.9 g/mol

e = 55.9 × 3 / (231.7 + 12 × 2) × 100%
e = 167.7 / 255.7 × 100%
e = 65.58%

[2 marks] 65.58%
[1 mark] 231.7 and 12 and 55.9

Answer 81. What colour does lithium produce during a flame test? [1]

Lithium ions produce a crimson red colour in a flame.

red

Answer 82. Identify all particles that are reduced in the half-equations provided.

2Cl⁻ → Cl₂ + 2e⁻
Mn⁵⁺ + 3e⁻ → Mn²⁺ [1]

A particle gains electrons when it is reduced. In these half-equations Mn⁵⁺ gains electrons.

Mn⁵⁺

Answer 83. Name the substance that iron needs to rust apart from water. [1]

Rusting is the corrosion of iron and it occurs when iron has access to both water and oxygen.

oxygen

Answer 84. Provide a chemical equation for the electrolysis of copper(II) chloride. [1]

During many of the electrolysis reactions, pure elements are produced. Since copper chloride contains copper and chlorine elements, copper metal and chlorine gas are produced during this reaction.

CuCl₂ → Cu + Cl₂

Answer 85. What are the formulae of ions participating in oxidation and reduction reactions at relevant electrodes during the electrolysis of potassium bromide solution? [2]

During the electrolysis of ionic solutions, multiple positive and negative ions compete to react at relevant electrodes. A more reactive ion participates in a relevant reaction involving it.

Metal ions follow the reactivity series, just in an opposite way, meaning the most reactive metals have the least reactive ions and vice versa. For negative ions, in many common reactions it is reasonable to assume that the larger oxygen-containing ions like sulphate are less reactive than the single-atom ions like chloride.

In a potassium bromide solution there are K⁺, Br⁻, H⁺, OH⁻ ions. H⁺ and Br⁻ are the more reactive ones that participate in redox equations at the electrodes.

[1 mark] H⁺
[1 mark] Br⁻

Answer 86. Name two main factors that affect the voltage created by a chemical cell. [2]

The voltage created at the cell is influenced by the the reactions happening in a cell and electrodes used.

[1 mark] reactions
[1 mark] electrodes

Answer 87. Balance equation CH₃OH + O₂ → CO₂ + H₂O. [1]

CH₃OH + O₂ → CO₂ + 2H₂O
CH₃OH + 1.5O₂ → CO₂ + 2H₂O
2CH₃OH + 3O₂ → 2CO₂ + 4H₂O

2CH₃OH + 3O₂ → 2CO₂ + 4H₂O

Answer 88. Name three fractions of crude oil. [3]

Petroleum gases are the least dense fraction of crude oil. We mainly use these gases for heating and cooking. Petrol is fuel for cars and power equipment. Kerosene powers planes. Diesel is fuel for vehicles like cars, trucks, and buses. Heavy fuel oil fuels ships and power plants.

[1 mark] petroleum gases
[1 mark] petrol
[1 mark] kerosene
[1 mark] diesel
[1 mark] heavy fuel oil
[1 mark] bitumen

Answer 89. Gareth reacted substance X with but-2-ene to produce C₄H₉Cl. Name X. [1]

The substance X that Gareth used to react with but-2-ene to produce C₄H₉Cl is HCl.

hydrogen chloride

Answer 90. Discuss how a reduction in national grape yield in California can affect local ethanol prices. [3]

If the yield of grapes decreases, the amount of them available for fermentation to produce ethanol will also reduce, leading to a decrease in the overall supply of ethanol. As a result of the decreased supply, the price of ethanol is likely to increase due to increased demand for the limited available supply.

[1 mark] using grapes in ethanol production
[1 mark] decreased supply of ethanol
[1 mark] higher ethanol price

Answer 91. Miko drew a polymer structure provided in the image. What needs adding to his diagram? [1]

Miko needs to indicate that the repeating unit repeats throughout the polymer by adding a letter "n" outside the brackets.

letter "n" outside brackets

Answer 92. Name the compound that is commonly used to test for bromide ions in a solution. [1]

Halide ions can be identified by adding silver nitrate with diluted nitric acid to their solutions. Presence of fluoride ions produces no precipitate, chloride - white AgCl precipitate, bromide - yellowish AgBr, iodide - yellow AgI.

silver nitrate

Answer 93. What colour precipitate does mixing a NaOH solution with a CuCl₂ solution form? [1]

In the presence of Cu²⁺ ions NaOH forms light blue precipitate.

blue

Answer 94. Compare the biodegradability of paper and plastic. [1]

Biodegradability is the ability of a material to break down naturally in the environment. Paper is biodegradable and can break down within a few weeks to a few months. Plastic, on the other hand, can take hundreds of years to break down.

Paper is biodegradable, plastic is not.

Answer 95. Which of the following materials can be recycled by crushing and melting to produce granules?

glass, wood, paper, metal, concrete, plastic [1]

The materials recycled by crushing and melting to produce granules are metal, glass and plastic.

metal, glass, plastic

Answer 96. Describe how a coastal city without rivers or underground water might obtain drinking water. [2]

In some areas, only sea water is available, which needs to be desalinated before it becomes potable. Desalination is an energy-consuming process that can be performed using distillation or reverse osmosis, making it expensive to provide drinking water via this route.

[1 mark] sea water
[1 mark] desalination

Answer 97. Over time sediments have absorbed large amounts of carbon dioxide. Name two examples of such deposits. [2]

Examples of deposits that have absorbed large amounts of carbon dioxide over time are fossil fuels and carbonate-rich minerals.

[1 mark] fossil fuels
[1 mark] carbonate-rich minerals

Answer 98. Describe the effects of sulphur dioxide on human health. [1]

Sulfur dioxide (SO₂) is a toxic gas that can cause respiratory problems when inhaled. It can irritate the eyes, nose, throat, and lungs and aggravate respiratory conditions such as asthma. Long-term exposure to high levels of SO₂ can lead to chronic bronchitis and reduced lung function.

respiratory problems

Answer 99. Describe the impact of burning fossil fuels on climate. [2]

Burning fossil fuels produces carbon emissions and increases carbon footprint. As a result, the greenhouse effect may increase.

[1 mark] increased carbon footprint
[1 mark] increased greenhouse effect

Answer 100. Name the compound essential in the production of ammonium salts. [1]

The compound essential in the production of ammonium salts is ammonia. We can produce ammonia during the reaction of nitrogen gas and hydrogen. We can convert it into ammonium salts such as ammonium nitrate and sulphate through a series of chemical reactions.

ammonia

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