The West African Examinations Council (WAEC) Chemistry Practical exam is one of the most anticipated papers for science students. With this detailed guide, we will walk you through the likely WAEC Chemistry practical questions for 2024, provide sure answers, and offer solutions to theoretical aspects. By the end of this article, you will be better prepared for the exam, understand the pattern, and gain confidence to achieve excellent results.
Key Components of WAEC Chemistry Practical Exam
The Chemistry practical exam typically focuses on three main components:
- Titration (Volumetric Analysis)
- Qualitative Analysis (Salt Analysis)
- Simple Experiments and Calculations (Physical and Chemical Properties)
Let’s break down these sections with questions and answers based on past trends.
1. Titration (Volumetric Analysis)
In the titration section, students are given two solutions: an acid and a base. They are required to carry out titration, record their results, and calculate various values like molarity or concentration.
Sample Question:
You are provided with a solution of HCl (Hydrochloric acid) and NaOH (Sodium hydroxide). The HCl has a molarity of 0.05 M, and you are to titrate 25.0 cm³ of NaOH with it. Your aim is to determine the molarity of NaOH.
Steps to Solve:
- Fill the burette with HCl solution and note the initial reading.
- Pipette 25.0 cm³ of NaOH into a conical flask and add a few drops of phenolphthalein indicator (color changes from pink to colorless at endpoint).
- Titrate the NaOH against HCl, while swirling the flask until the endpoint is reached.
- Record your final burette reading and calculate the volume of HCl used.
Calculation:
- Molarity of HCl (M₁) = 0.05 M
- Volume of HCl used (V₁) = final burette reading – initial burette reading (e.g., 20.5 cm³ – 0.0 cm³ = 20.5 cm³)
- Volume of NaOH (V₂) = 25.0 cm³
Using the titration formula:
M1×V1=M2×V2M₁ \times V₁ = M₂ \times V₂Where M₂ is the molarity of NaOH:
0.05×20.5=M2×25.00.05 \times 20.5 = M₂ \times 25.0 M2=0.05×20.525.0=0.041MM₂ = \frac{0.05 \times 20.5}{25.0} = 0.041 MThus, the molarity of NaOH is 0.041 M.
2. Qualitative Analysis (Salt Analysis)
This section tests your ability to analyze salts and identify their ions based on chemical reactions and observation of physical properties.
Sample Question:
You are provided with a sample of a salt solution. Perform the following tests and record your observations and inferences.
- Test for Anions: Add a few drops of barium chloride solution to the salt solution. Follow this by adding dilute hydrochloric acid.
Observation: A white precipitate is formed, which dissolves in dilute hydrochloric acid.
Inference: The presence of sulfate ions (SO₄²⁻) is confirmed.
- Test for Cations: Add sodium hydroxide solution to a portion of the salt solution dropwise and then in excess.
Observation: A gelatinous white precipitate is formed, which dissolves in excess sodium hydroxide.
Inference: The cation is likely aluminum (Al³⁺).
3. Simple Experiments and Calculations
This section might involve determining the physical or chemical properties of a substance or conducting a reaction.
Sample Question:
A sample of magnesium was reacted with dilute hydrochloric acid, and the volume of hydrogen gas produced was measured at room temperature and pressure.
- Given: Mass of magnesium = 0.24 g, Volume of hydrogen produced = 240 cm³, Molar mass of Mg = 24 g/mol, Molar volume of a gas at room temperature = 24,000 cm³.
Solution:
- First, calculate the number of moles of magnesium:
Number of moles of Mg=0.24g24g/mol=0.01mol\text{Number of moles of Mg} = \frac{0.24 g}{24 g/mol} = 0.01 mol
- According to the balanced chemical equation:
Mg+2HCl→MgCl2+H2Mg + 2HCl \rightarrow MgCl₂ + H₂1 mole of Mg produces 1 mole of H₂ gas. Therefore, 0.01 mol of Mg will produce 0.01 mol of H₂.
- Since the molar volume of a gas at room temperature is 24,000 cm³, the volume of hydrogen produced is:
0.01mol×24,000cm3/mol=240cm30.01 mol \times 24,000 cm³/mol = 240 cm³Thus, the calculated volume of hydrogen matches the experimental value.
WAEC Chemistry Practical FAQs
What should I focus on for the WAEC Chemistry practical?
Focus on titration, qualitative analysis (salt tests), and basic chemical reactions involving common acids, bases, and salts. Be familiar with common indicators like methyl orange and phenolphthalein, and practice simple calculations involving molarity and gas volumes.
How can I prepare for the titration section?
Practice titration using acids and bases with known concentrations. Ensure you are comfortable with reading burettes accurately and performing molarity calculations. Also, know the reactions between common acids and bases.
What materials do I need for the practical?
You’ll need basic laboratory equipment like a burette, pipette, conical flask, beakers, and reagents such as acids, bases, and indicators. Familiarize yourself with these in advance to avoid confusion during the exam.
How are practical marks awarded?
Marks are typically awarded for accuracy in titration readings, correct observations in qualitative analysis, and proper calculations in theoretical sections. Proper documentation and neat work are also important.
Are there any common mistakes to avoid?
Yes, students often forget to de-bubble the burette during titration, misinterpret the color changes in indicators, or fail to clean apparatus properly between experiments. Always ensure you’re following lab safety and best practices.
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Conclusion
The WAEC Chemistry practical exam demands a good grasp of fundamental laboratory techniques, chemical reactions, and theoretical understanding. With this guide and consistent practice, you are well on your way to success in the 2024 WAEC Chemistry exam. For more details on WAEC preparations, you can check out official resources on the WAEC website or explore other useful guides.