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Questions and Answers
What is the primary function of the electrolyte in an electrolytic cell?
Which electrode is positively charged in an electrolytic cell?
What type of current is required for electrolysis to take place?
In the electrolysis of molten Lead (II) Bromide, what is produced at the anode?
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What occurs at the cathode during electrolysis?
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Which gas is produced at the cathode when dilute sulfuric acid undergoes electrolysis?
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In the electrolysis of aqueous sodium chloride, which product is obtained at the anode?
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During electrolysis, what directly causes the movement of charge in the electrolyte?
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What role does a power source play in an electrolytic cell?
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In the electrolysis of water, what is the ratio of hydrogen to oxygen produced?
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What is the primary reason for adding sulfuric acid to water before electrolysis?
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Which of the following describes the half-equation at the anode during electrolysis of Lead (II) Bromide?
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Which process describes the gain and loss of electrons at the electrodes during electrolysis?
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During the electrolysis of aqueous copper (II) sulfate, which species is discharged at the anode?
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What type of reaction occurs within a hydrogen-oxygen fuel cell?
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In the electrolysis of sodium chloride solution, which gas is produced at the cathode?
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Which of the following statements best describes an endothermic reaction?
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What is the role of activation energy in chemical reactions?
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What happens to the concentration of copper ions in a copper electrode electrolysis setup?
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Which of the following is a characteristic of a physical change?
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In bond breaking and making, what is true of exothermic reactions?
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What is the main waste product of a hydrogen-oxygen fuel cell?
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What describes the energy changes during an exothermic reaction?
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When hydroxide ions are discharged in electrolysis, what is the result?
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Which reaction pathway diagram indicates a reaction that absorbs energy?
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Why is hydrogen considered a clean fuel?
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In the electrolysis of molten substances, what happens to the ions?
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Which factor does NOT increase the rate of reaction?
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What is the main role of a catalyst in a chemical reaction?
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In collision theory, what is required for a reaction to occur between reactant particles?
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Which of the following substances is oxidized in a redox reaction?
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Which statement about photosynthesis is correct?
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What happens to the rate of photosynthesis when carbon dioxide concentration decreases?
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In what direction does phloem transport sugars in a plant?
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Which condition does NOT speed up transpiration in plants?
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What is the primary function of red blood cells?
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Which type of blood vessel has the highest blood pressure?
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What consequence does coronary heart disease primarily have on the heart?
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Which of the following components makes up the majority of blood?
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What happens to the heart rate during exercise?
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Study Notes
Electrolysis
- Decomposition of an ionic compound in either molten or aqueous solution by applying an electric current
- Liquid metals and graphite can conduct electricity due to the presence of free electrons that can move around
- The apparatus used is called an electrolytic cell, which changes electrical energy into chemical energy
Parts of an Electrolytic Cell
- Electrolyte: The molten or aqueous substance that undergoes electrolysis
- Direct current: Supplied by a power source (like a battery)
-
Electrodes: Points where the electric current enters and exits the cell. Often made of graphite, which is unreactive.
- Anode: Positive electrode
- Cathode: Negative electrode
How Electrolysis Works
- Electrons flow from the negative terminal to the positive terminal of the battery
- Ions move through the electrolyte to carry the current
- Positive ions (cations) move towards the negative cathode, while negative ions (anions) move towards the positive anode
Comparing Metallic and Electrolytic Conductivity
- Metallic conductivity: Charge is carried by electrons moving through a solid material
- Electrolytic conductivity: Charge is carried by ions moving through a liquid
Electrolysis Examples
-
Molten Lead (II) Bromide:
- Formula: PbBr2
- Gaseous product: Br2
- Half equations:
- Cathode: Pb2+ + 2e- → Pb (l)
- Anode: 2Br- - 2e- → Br2 (g)
- Balanced equation: Pb2+ + 2Br- → Pb (l) + Br2 (g)
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Dilute Sulfuric Acid:
- Water is a poor conductor of electricity due to its limited number of ions
- Electrolysis requires a Hofmann Voltameter to separate the gases produced
- Ions present: H+, OH-, SO42-
- At the cathode, only one ion can be discharged, and OH- is discharged over SO42- due to its relative ion stability
- Reaction: 2H2O (l) → 2H2 (g) + O2 (g)
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Aqueous Sodium Chloride:
- Four ions present: Na+, Cl-, OH-, H+
- Hydrogen gas is produced at the cathode and chlorine gas is produced at the anode
- Products differ from molten sodium chloride electrolysis
-
Molten Ionic Compounds:
- Electrolysis requires heating the salt to ensure it can conduct electricity
- General Product Rules:
- Cathode: Metal solid or hydrogen (the first element in the chemical formula)
- Anode: Non-metal gas (the second element in the chemical formula)
-
Aqueous Solutions (including acids):
- Products differ from molten electrolysis due to the presence of water, which breaks down into ions
- Hydrogen and hydroxide ions compete with ions from the acid or salt to be discharged at the electrodes
Aqueous Copper (II) Sulfate Electrolysis
- Using inert electrodes like carbon or graphite:
- Copper metal is deposited on the cathode
- Copper is less reactive than hydrogen, therefore discharged at the cathode: Cu2+ (aq) + 2e- → Cu (s)
- Hydroxide ions are discharged, not sulfate ions: 4OH- → 2H20 + O2 + 4e-
- Observations:
- The blue solution color will fade overtime as copper ions are discharged
- Electrolyte solution becomes more acidic as hydroxide ions are discharged
- Using copper electrodes:
- Cathode gains mass as copper deposits on it: Cu2+ (aq) + 2e- → Cu (s)
- Anode loses mass as copper dissolves from it: Cu (s) → Cu2+ (aq) + 2e-
- The blue solution color does not change as the concentration of copper ions remains constant in the solution
Ionic Half-equations
- Anode: An anion (negatively charged ion) gives up electrons to become neutral (oxidation)
- Example: Cl- gives up one electron to become Cl
- Cathode: A cation (positively charged ion) accepts electrons to become a neutral atom (reduction)
- Example: Mg2+ accepts two electrons to become Mg
Hydrogen-Oxygen Fuel Cells
- Device that continuously converts chemical energy into electrical energy using a chemical reaction
- Hydrogen-Oxygen Fuel Cell: uses the combustion reaction of hydrogen and oxygen gas to create energy for electricity, with water as the only product
- Reaction: 2H2 (g) + O2 (g) → 2H2O (l)
Advantages and Disadvantages of Hydrogen-Oxygen Fuel Cells
-
Advantages:
- Clean fuel: Only produces water as waste
- Lower flammability than petrol
- More efficient technology
- Convenient for heavy transport and trains
- Produces more energy per gram than any other fuel
-
Disadvantages:
- Difficult and potentially dangerous to store and transport hydrogen gas
- Requires widespread distribution of hydrogen filling stations
- Difficulty in producing the fuel cell itself
- Large fuel tank required
Exothermic Reactions
- Reactions where thermal energy is released into the surroundings, causing an increase in the temperature of the surroundings
- Feels hot
- "Exothermic" means "energy exits the reaction"
Endothermic Reactions
- Reactions that absorb thermal energy from the surroundings, causing a decrease in the temperature of the surroundings
- Feels cold
- "Endothermic" means "energy enters the reaction"
Reaction Pathways (Energy Level) Diagrams
-
Exothermic reactions:
- Reactant energy is higher than the product energy
- Arrow points down: Shows energy is released
-
Endothermic reactions:
- Reactant energy is lower than the product energy
- Arrow points upwards: Shows energy is absorbed
Enthalpy Change (∆H)
- Enthalpy: The thermal energy content of a system
-
Enthalpy change: The transfer of energy during a reaction
- Exothermic: Negative enthalpy change
- Endothermic: Positive enthalpy change
Activation Energy
- The minimum energy required for colliding particles to react (cause a chemical reaction to occur)
- Activation energy is represented on the energy level diagram
- Important: Some bonds must be broken before new bonds can be formed
- Activation energy must be overcome before a reaction can proceed, regardless of whether it is exothermic or endothermic
How to Draw Reaction Pathway Diagrams
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Label the axes:
- X-axis: Reaction coordinate
- Y-axis: Energy
- Draw reactant and product lines: The lines represent the energy levels of the reactants and products
- Add a hump: This represents the activation energy needed for the reaction to occur
- Label the activation energy and enthalpy change: Clearly indicate these values on the diagram.
Bond Breaking and Making
- Bond Breaking: Requires energy to be absorbed (endothermic)
- Bond Making: Releases energy (exothermic)
- Stronger bonds require more energy to break and release more energy when new bonds are formed (high bond energy)
Physical Changes
- No new substance is formed
- The substances present remain chemically unchanged
- Usually easy to reverse
- Often easy to separate
- May involve the transfer of heat
Chemical Changes
- Result of a chemical reaction where a new substance is formed
- Usually difficult to reverse
- Energy can be given out or taken in (exothermic or endothermic)
Rate of Reaction
- Reaction rate is measured as the speed at which reactants become products.
- Factors influencing the rate of reaction:
- Concentration: Higher reactant concentration means more particle collisions and faster reaction.
- Pressure (gaseous reactions): Increasing pressure leads to reduced space between particles, boosting collision frequency and chances for successful collisions.
- Surface Area (solid reactants): Larger surface area exposes more reactant particles for collisions, increasing reaction opportunity.
- Temperature: Higher temperature increases particle kinetic energy, leading to more frequent and successful collisions.
- Catalyst: Provides an alternative reaction pathway with lower activation energy, resulting in a greater proportion of successful collisions. Catalysts are not reactants and remain unchanged throughout the reaction, making them reusable.
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Collision Theory: Chemical reactions occur due to collisions between reacting particles, with two essential criteria:
- Correct orientation of reactant particles.
- Sufficient energy to break reactant bonds (known as activation energy).
-
Factors influencing collision success:
- Particle concentration: Higher concentration leads to greater collision probability.
- Collision frequency: Determined by particle movement and energy.
- Kinetic energy: Higher energy increases the likelihood of overcoming the activation energy barrier.
- Activation energy: Minimal energy required for successful collisions.
-
Practical methods for investigating reaction rate:
- Measuring the rate at which reactants are used up.
- Measuring the rate at which products are formed.
-
Properties changing during the reaction:
- Gas production: Measure gas volume as a reaction progresses, as in the magnesium ribbon experiment.
- Color or turbidity change: Changes in the reaction solution's appearance.
- Mass change: Tracking the mass of reactants and products.
Redox
- Redox reactions: Reactions involving simultaneous oxidation and reduction.
- Oxidation: Gain of oxygen.
- Reduction: Loss of oxygen.
-
Oxidation and Reduction with electrons:
- Oxidation number: Represents the positive charge on a metal ion.
- Oxidation: Loss of electrons, resulting in an increase in oxidation number.
- Reduction: Gain of electrons, leading to a decrease in oxidation number.
- Oxidising agent: Oxidises another substance and gets reduced itself; typically a non-metal.
- Reducing agent: Reduces another substance and gets oxidised itself; typically a metal.
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Identifying oxidation and reduction:
- Oxidation: Increase in charge or oxidation number.
- Reduction: Decrease in charge or oxidation number.
Photosynthesis
- Photosynthesis: The process by which plants create carbohydrates from raw materials, using light energy.
- Equation: Carbon dioxide + water → oxygen + glucose in the presence of light and chlorophyll.
- Chlorophyll: A green pigment found in chloroplasts, transferring light energy for carbohydrate synthesis.
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Uses of glucose:
- Sucrose: For transport in the phloem.
- Nectar: Attracting insects for pollination.
- Starch: Energy storage.
- Cellulose: Building cell walls.
- Glucose: Used in respiration for energy release.
- Proteins: Growth.
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Ions: Glucose combines with soil minerals to form essential compounds:
- Nitrates for producing amino acids for proteins.
- Magnesium ions for chlorophyll synthesis.
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Limiting factors for photosynthesis:
- Light: Increases in photosynthesis rate until a point of saturation.
- Temperature: Increases in photosynthesis rate with temperature until enzymes denature.
- Carbon dioxide: Increases in photosynthesis rate until a point of saturation.
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Hydrogencarbonate indicator: Used to detect changes in carbon dioxide concentration.
- Red: Normal concentration.
- Yellow: Increased concentration.
- Purple: Decreased concentration.
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Gas exchange in leaves:
- Bright light: Photosynthesis exceeds respiration, with carbon dioxide uptake and oxygen release. Indicator turns purple due to carbon dioxide reduction.
- Low light: Photosynthesis and respiration rates are equal (compensation point), resulting in no net gas exchange. The indicator remains red.
- Darkness: Only respiration occurs, with oxygen uptake and carbon dioxide release. Indicator turns yellow due to carbon dioxide increase.
Leaf Structure
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Adaptation for photosynthesis:
- Large surface area: For maximizing light absorption.
- Thin structure: Short diffusion distance for gases.
- Chlorophyll: Present in chloroplasts, capturing light energy.
- Veins: Providing water and removing excess water.
- Stomata: Controlling gas exchange and water loss.
Transport in Plants
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Xylem and Phloem: The two main transport tissues in plants.
- Xylem: Transports water and dissolved minerals upwards; dead cells.
- Phloem: Transports sugars both upwards and downwards; living cells.
Water Uptake in Plants
- Root hair cells: Tiny hairs providing a large surface area for water and mineral ion absorption by osmosis.
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Pathway for water movement:
- Root hair cell
- Root cortex
- Xylem
- Leaves
- Air
Transpiration
- Transpiration: Loss of water vapour from plant leaves, involving evaporation from mesophyll cells and diffusion through stomata.
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Factors affecting transpiration rate:
- Temperature: Warmer temperatures increase evaporation and diffusion.
- Humidity: High humidity reduces the concentration gradient between the inside and outside of the leaf, slowing down transpiration.
- Wind speed: Increased wind speeds remove water vapour, maintaining a low concentration gradient outside the leaf and enhancing diffusion rate.
- Wilting: Occurs when transpiration exceeds water uptake, leading to flaccid cells and a drooping plant.
- Potometer: Used to measure water uptake by the plant, recording the distance travelled by an air bubble in a tube connected to the plant.
Translocation
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Translocation: Movement of sucrose and other substances (like amino acids) throughout the plant.
- Glucose produced in leaves is converted to sucrose and transported through the phloem.
- Sources: Parts of the plant that release or produce sucrose and amino acids.
- Sinks: Parts of the plant that use or store sucrose and amino acids.
Transport in Animals
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Circulatory systems: Composed of blood vessels, a pump (heart), and valves to ensure one-way blood flow.
- Single circulation (Fish): Two-chambered heart pumps blood to gills, then to the body, and back to the heart.
- Double circulation (Mammals): Four-chambered heart pumps blood to the lungs to pick up oxygen and then back to the heart, then oxygenated blood is pumped to all body cells.
-
Advantages of double circulation:
- Maintains higher blood pressure, allowing for efficient oxygen delivery.
The Heart
-
Response to exercise:
- Heart: Increased heart rate, dilated arteries, increased blood flow to muscles, enhanced oxygen and glucose delivery to muscles, and increased carbon dioxide removal.
- Lungs: Increased breathing rate and depth, facilitating increased oxygen uptake by red blood cells and delivery to muscles, as well as enhanced carbon dioxide removal.
-
Explanation of exercise response:
- Heart: Increased demand for oxygen and glucose delivery to cells for respiration and energy production.
- Lungs: Increased need for oxygen uptake for respiration and energy production.
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Heart parts:
- Right atrium: Receives deoxygenated blood from the body.
- Right ventricle: Pumps deoxygenated blood to the lungs.
- Left atrium: Receives oxygenated blood from the lungs.
- Left ventricle: Pumps oxygenated blood to the body.
- Valves: Ensure one-way blood flow.
-
Pathway of blood:
- Left atrium → left ventricle → aorta → vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein.
-
Monitoring heart activity:
- Pulse rate: Measuring heartbeats per minute.
- Heart sounds (lub-dub): Sounds of the heart valves closing.
- ECG (Electrocardiogram): Recording electrical activity in the heart.
Coronary Heart Disease (CHD)
-
CHD: Blockage of coronary arteries, which supply heart muscle with oxygen and glucose.
- Atheroma: Fatty deposits in artery walls, composed of cholesterol buildup.
- Consequences: Stiffening of artery walls, narrowing of the lumen, restricting blood flow, causing blockages, increasing blood pressure, damaging artery lining, and potentially leading to blood clots.
-
Risk factors:
- Smoking
- Diet (high animal fats)
- Lack of exercise
- Age
- Males
- Stress
- Genetic predisposition
- Myocardial infarction (Heart Attack): Reduced oxygen supply to the heart muscle, a symptom of CHD caused by coronary artery blockage.
Blood Vessels
- Arteries: Carry blood away from the heart, have thick muscular walls, and maintain high blood pressure.
- Veins: Carry blood towards the heart, have thinner, more flexible walls, and have valves to prevent backflow due to lower blood pressure.
- Capillaries: Microscopic blood vessels connecting arteries and veins, facilitate the exchange of oxygen and nutrients between blood and cells.
Blood
-
Components of blood:
- Red blood cells: Transport oxygen, contain haemoglobin, a protein molecule bound to iron atoms, which reversibly binds to oxygen.
- Plasma: Transports blood cells, carbon dioxide, urea, nutrients, ions, and hormones.
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White blood cells: Defending against disease and clearing up dead cells.
- Phagocytes: Engulf and digest pathogens.
- Lymphocytes: Produce antibodies to destroy pathogens.
- Platelets: Involved in blood clotting, preventing pathogen entry and blood loss.
- Blood clotting: A process involving platelets and other clotting factors to form a clot at the site of injury.
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