Possible 6 mark questions for the end of year exam

1. Describe the structure of an atom and explain how elements are arranged in the periodic table.

✅ Model Answer:

An atom consists of a central nucleus made up of protons and neutrons, surrounded by electrons that orbit the nucleus in electron shells. The number of protons in the nucleus determines the atomic number, which is unique to each element. The periodic table arranges elements in order of increasing atomic number. Elements are grouped into periods (horizontal rows) that represent the number of electron shells, and groups (vertical columns) based on their chemical properties and the number of electrons in their outer shell.

🎯 Mark Scheme Guidance:

• 1–2 marks: Mentions the nucleus and electron shells.

• 3–4 marks: Describes the role of protons, neutrons, and electrons.

• 5–6 marks: Clearly explains the periodic table arrangement and how elements are classified into periods and groups.

🧪 2. Explain how the reactivity of alkali metals changes as you go down the group.

✅ Model Answer:

As you go down Group 1 (alkali metals) in the periodic table, the reactivity of the metals increases. This is because the outer electron is further away from the nucleus, making it easier to lose. The shielding effect of inner electrons also increases, reducing the attraction between the outer electron and the nucleus. As a result, alkali metals such as lithium, sodium, and potassium become more reactive as you move down the group. This increased reactivity is shown in the violent reactions of potassium and cesium with water.

🎯 Mark Scheme Guidance:

• 1–2 marks: States that reactivity increases down the group.

• 3–4 marks: Describes the effect of distance and shielding on reactivity.

• 5–6 marks: Explains both atomic structure and trends in reactivity, including an example.

🔬 3. Describe what happens during a neutralisation reaction between an acid and a base.

✅ Model Answer:

In a neutralisation reaction, an acid reacts with a base (or alkali) to produce water and a salt. The acid provides hydrogen ions (H⁺), and the base provides hydroxide ions (OH⁻). When these ions combine, they form water (H₂O). The remaining ions from the acid and base combine to form a salt. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the products are water and sodium chloride (NaCl). This reaction is exothermic and releases energy.

🎯 Mark Scheme Guidance:

• 1–2 marks: Describes the general concept of acid and base reaction.

• 3–4 marks: States the products (water and salt) and mentions ions.

• 5–6 marks: Explains the specific process of ion interaction, with a detailed example.

⚖ 4. Explain how the rate of a chemical reaction can be increased.

✅ Model Answer:

The rate of a chemical reaction can be increased by several factors:

1. Increasing temperature: This gives particles more kinetic energy, causing them to collide more frequently and with greater energy, increasing the likelihood of successful collisions.

2. Increasing concentration: A higher concentration of reactants means there are more particles in a given volume, leading to more frequent collisions.

3. Increasing surface area: Smaller particles (e.g. powdered solids) have more surface area for collisions, leading to more effective reactions.

4. Using a catalyst: A catalyst provides an alternative reaction pathway with a lower activation energy, increasing the rate of reaction without being consumed.

🎯 Mark Scheme Guidance:

• 1–2 marks: Mentions one or two factors that affect reaction rate.

• 3–4 marks: Describes how temperature, concentration, or surface area affects the rate.

• 5–6 marks: Explains all factors in detail, including catalysts.

💨 5. Describe the process of fractional distillation and how it is used to separate liquids.

✅ Model Answer:

Fractional distillation is a process used to separate a mixture of liquids with different boiling points. The mixture is heated, and the liquid with the lowest boiling point evaporates first. The vapour rises through a column, which is cooler at the top. As the vapour cools, it condenses back into liquid form. The liquid is then collected in different fractions, based on their boiling points. This process is used to separate mixtures such as crude oil into its various components, like petrol, diesel, and kerosene.

🎯 Mark Scheme Guidance:

• 1–2 marks: Mentions separating liquids and using boiling points.

• 3–4 marks: Describes the process of heating, vaporisation, and condensation.

• 5–6 marks: Explains the process in detail, including the use of a fractionating column and specific examples.

🔋 6. Explain the difference between exothermic and endothermic reactions, and give an example of each.

✅ Model Answer:

Exothermic reactions release energy to the surroundings, usually in the form of heat, making the surroundings feel warmer. An example is the combustion of methane, where methane reacts with oxygen to release energy as heat and light. On the other hand, endothermic reactions absorb energy from the surroundings, causing a temperature drop. An example is the reaction between ammonium nitrate and water, which is used in cold packs. In both types of reactions, the total energy change is related to the difference between the energy required to break bonds and the energy released when new bonds form.

🎯 Mark Scheme Guidance:

• 1–2 marks: Describes the basic difference between exothermic and endothermic reactions.

• 3–4 marks: Gives clear examples of each type of reaction.

• 5–6 marks: Explains energy changes in terms of bond breaking and forming, with full examples.

🌍 7. Describe how chemical reactions are used in the process of electrolysis.

✅ Model Answer:

Electrolysis is the process of using an electric current to drive a non-spontaneous chemical reaction. In electrolysis, two electrodes (positive anode and negative cathode) are placed in an electrolyte, a solution containing ions. When current passes through the electrolyte, ions move towards the electrodes. At the anode, negative ions lose electrons and are oxidised (e.g. chloride ions forming chlorine gas). At the cathode, positive ions gain electrons and are reduced (e.g. copper ions forming copper metal). Electrolysis is used in processes such as the extraction of metals and the production of chlorine and hydrogen.

🎯 Mark Scheme Guidance:

• 1–2 marks: Mentions the use of electric current and electrodes.

• 3–4 marks: Describes the movement of ions and the processes of oxidation and reduction.

• 5–6 marks: Provides a clear explanation of the electrolysis process, with specific examples.