Mandatory Experiments Exam Tips (Leaving Cert Chemistry): Revision Notes

Mandatory Experiments Exam Tips

There are 31 mandatory experiments for LC Chemistry.

• They are examined in Section A of the paper.
• You must complete two out of three questions for a total of 50 marks. Note: Questions about experiments may also appear in Section B.

Question 1

Question 1 covers titration and volumetric analysis. It typically involves carrying out calculations based on experimental titration results.

Mandatory Experiments

Topic - Volumetric Analysis

4.1 - Preparation of a Standard Solution of Sodium Carbonate

4.2 - Standardisation of a Hydrochloric Acid Solution

4.2a - Titration of Hydrochloric Acid with Sodium Hydroxide to Form Sodium Chloride

4.3 - Determination of the Concentration of Ethanoic Acid in Vinegar

4.4 - Determination Percentage Water of Crystallisation in a Sample of Hydrated Sodium Carbonate

4.5 - A Potassium Manganate (VII) / Ammonium Iron (II) Sulphate Titration

4.6 - Determination of the Amount of Iron in an Iron Tablet

4.7 - An Iodine and Sodium Thiosulfate Titration

4.8 - Determination of the Percentage of Hypochlorite in Bleach

Topic - Environmental Chemistry: Water

9.3 - Estimation of Total Hardness using Ethylenediaminetetraacetic Acid

9.4 - Estimation of Dissolved Oxygen by Redox Titration

Advice for Answering

Titration Procedures:

Be confident with the steps of setting up and performing titrations. This includes:

• Rinsing and filling a burette and pipette correctly.

• Measuring the correct volume of solution (using a pipette).

• Adding titrant to the analyte and identifying the endpoint using an appropriate indicator.

• Recording titration volumes accurately from the burette. Understanding Titration Types:

• Acid-Base Titrations (e.g., standardisation of $HCl$ using $Na₂CO₃$).

• Redox Titrations (e.g., potassium manganate (VII) titration to determine iron content).

• Water Titrations (e.g., determining water hardness with EDTA). Preparation of Standard Solutions:

You may be asked about how to prepare a standard solution, such as sodium carbonate ($Na₂CO₃$), for use in a titration.

Common Calculations

Molarity (M)

Use the formula:

$$M = \frac{n}{V}$$

where $n$ is the number of moles and $V$is the volume in litres.

Ensure units are correctly converted to litres and moles when necessary.

Moles of a Substance

Given by:

$$\text{Moles} = M \times V$$

Calculate moles from concentration (molarity) and volume.

Balanced Equations

Use stoicheiometry to relate the moles of titrant and analyte. Pay attention to the molar ratios in the balanced chemical equations.

Dilution Calculations

When the question involves diluting a solution, remember:

$$M_1V_1 = M_2V_2$$

• Where $M_1$ and $V_1$ are the molarity and volume before dilution
• and $M_2$ and $V_2$ are after dilution.

Question 2

Question 2 in Section A focuses on the seven mandatory organic experiments in the Leaving Cert Chemistry syllabus. The question typically involves knowing the procedures, chemicals, apparatus, and reactions involved.

Mandatory Experiments

Topic - Organic Chemistry

7.1 - Recrystallisation of Benzoic Acid and Determination of its Melting Point

7.2 - Preparation of Soap

7.3 - Preparation and Properties of Ethene

7.4 - Preparation and Properties of Ethanal

7.5 - Preparation and Properties of Ethanoic Acid

7.6 - Extraction of Clove Oil from Cloves by Steam Distillation

7.7 - Separation of a Mixture of Indicators

Advice for Answering

Know Each Experiment:

For each experiment, ensure you can outline the steps clearly, name the key chemicals and apparatus used, and explain any reactions involved.

Understand Reaction Types:

• These experiments cover various organic reactions, such as addition, substitution, and esterification.
• Be able to explain the relevant chemical reactions, including balanced equations where needed. Make Summaries:

Given that the details of different experiments can be confusing, summarise each one in terms of:

• Method: A step-by-step guide.
• Chemicals Used: Reactants and products.
• Apparatus: Essential equipment.
• Key Concepts and Results: What the experiment demonstrates (e.g., dehydration, oxidation, or extraction).

Common Calculations

Percentage Yield:

Some experiments require calculating the percentage yield of a product:

$$\text{Percentage Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100$$

Ensure you can calculate actual and theoretical yields based on experimental data.

Purity Determination:

Recrystallisation experiments often require understanding how purity is determined, for example, by measuring the melting point of the recrystallised product.

Question 3

Question 3 in Section A covers the remaining mandatory experiments not addressed in Questions 1 and 2. These experiments span a range of topics from different areas of the syllabus, such as rates of reaction, equilibrium, water chemistry, and thermochemistry. While there is variation in the content, the exam questions in these experiments tend to be repetitive, making this a manageable question with good preparation.

Mandatory Experiments

Topic - Periodic Table and Atomic Structure

1.1 - Flame Tests

1.2 - Redox Reactions of Group VII Elements and Displacement Reactions of Metals

Topic - Chemical Bonding

2.1 - Tests for Anions in Aqueous Solutions

Topic - Stoicheiometry, Formulas and Equations

3.1 - Determination of the Relative Molecular Mass of a Volatile Liquid

Topic - Fuels and Heats of Reaction

5.1 - Determination of the Heat of Reaction of Hydrochloric Acid with Sodium Hydroxide

5.2 - Preparation and Properties of Ethyne

Topic - Rates of Reaction

6.1 - Rate of Production of Oxygen from Hydrogen Peroxide

6.2 - Effect of Concentration on Reaction Rate using Sodium Thiosulphate and Hydrochloric Acid

6.2a - Effect of Temperature on Reaction Rate using Sodium Thiosulphate and Hydrochloric Acid

Topic - Chemical Equilibrium

8.1 - Simple Experiments to Illustrate Le Chatelier's Principle

8.1a - Effects of Concentration Changes on the Equilibrium Mixture

Topic - Environmental Chemistry: Water

9.1 - Colorimetric Experiment to Estimate Free Chlorine in Swimming Pool Water or Bleach

9.2 - Determination of Total Suspended and Total Dissolved Solids in p.p.m.

9.2a - Determination of pH

Advice for Answering

Understand Each Experiment:

Be familiar with the procedures, chemicals, apparatus, and key concepts for each of the following mandatory experiments:

• Rates of Reaction: e.g., measuring reaction rates using sodium thiosulfate and hydrochloric acid.
• Equilibrium: e.g., demonstrating Le Chatelier's Principle.
• Water Analysis: e.g., determining water hardness or measuring dissolved oxygen.
• Thermochemistry: e.g., determining the heat of reaction between HCl and NaOH. Each experiment should be understood in terms of the procedure and the scientific principle it demonstrates.

Common Exam Patterns:

Because the exams tend to be repetitive, focus on practising past paper questions for these experiments. This will give you a strong sense of what is typically asked, such as:

• Why certain procedures are followed.
• Sources of error and how to minimise them.
• How the scientific concepts are illustrated by each experiment.

Common Calculations

Heat of Reaction:

For thermochemistry experiments, you will need to calculate heat change using:

$$q = mc\Delta T$$

Where:

• $q$ is heat energy
• $m$ is mass
• $c$ is the specific heat capacity
• $\Delta T$ is the temperature change.

Section A Questions 1-3 Overview

Overview of the Question	Mandatory Experiments
QUESTION 1: Question 1 covers titration and volumetric analysis. It typically involves carrying out calculations based on experimental titration results.	Topic • Volumetric Analysis 4.1 • Preparation of a Standard Solution of Sodium Carbonate 4.2 • Standardisation of a Hydrochloric Acid Solution 4.2a • Titration of Hydrochloric Acid with Sodium Hydroxide to Form Sodium Chloride 4.3 • Determination of the Concentration of Ethanoic Acid in Vinegar 4.4 • Determination Percentage Water of Crystallisation in a Sample of Hydrated Sodium Carbonate 4.5 • A Potassium Manganate (VII) / Ammonium Iron (II) Sulphate Titration 4.6 • Determination of the Amount of Iron in an Iron Tablet 4.7 • An Iodine and Sodium Thiosulfate Titration 4.8 • Determination of the Percentage of Hypochlorite in Bleach Topic • Environmental Chemistry: Water 9.3 • Estimation of Total Hardness using Ethylenediaminetetraacetic Acid 9.4 • Estimation of Dissolved Oxygen by Redox Titration
QUESTION 2: Question 2 in Section A focuses on the seven mandatory organic experiments in the Leaving Cert Chemistry syllabus. The question typically involves knowing the procedures, chemicals, apparatus, and reactions involved.	Topic • Organic Chemistry 7.1 • Recrystallisation of Benzoic Acid and Determination of its Melting Point 7.2 • Preparation of Soap 7.3 • Preparation and Properties of Ethene 7.4 • Preparation and Properties of Ethanal 7.5 • Preparation and Properties of Ethanoic Acid 7.6 • Extraction of Clove Oil from Cloves by Steam Distillation 7.7 • Separation of a Mixture of Indicators
QUESTION 3: Question 3 in Section A covers the remaining mandatory experiments not addressed in Questions 1 and 2. These experiments span a range of topics from different areas of the syllabus, such as rates of reaction, equilibrium, water chemistry, and thermochemistry. While there is variation in the content, the exam questions in these experiments tend to be repetitive, making this a manageable question with good preparation.	Topic • Periodic Table and Atomic Structure 1.1 • Flame Tests 1.2 • Redox Reactions of Group VII Elements and Displacement Reactions of Metals Topic • Chemical Bonding 2.1 • Tests for Anions in Aqueous Solutions Topic • Stoicheiometry, Formulas and Equations 3.1 • Determination of the Relative Molecular Mass of a Volatile Liquid Topic • Fuels and Heats of Reaction 5.1 • Determination of the Heat of Reaction of Hydrochloric Acid with Sodium Hydroxide 5.2 • Preparation and Properties of Ethyne Topic • Rates of Reaction 6.1 • Rate of Production of Oxygen from Hydrogen Peroxide 6.2 • Effect of Concentration on Reaction Rate using Sodium Thiosulphate and Hydrochloric Acid 6.2a • Effect of Temperature on Reaction Rate using Sodium Thiosulphate and Hydrochloric Acid Topic • Chemical Equilibrium 8.1 • Simple Experiments to Illustrate Le Chatelier's Principle 8.1a • Effects of Concentration Changes on the Equilibrium Mixture Topic • Environmental Chemistry: Water 9.1 • Colorimetric Experiment to Estimate Free Chlorine in Swimming Pool Water or Bleach 9.2 • Determination of Total Suspended and Total Dissolved Solids in p.p.m. 9.2a • Determination of pH