A student carries out a reaction between hydrogen and chlorine to produce hydrogen chloride. Write the word equation for this reaction, then explain why it is important that the student checks the hazard information for all substances involved before starting the experiment.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Hydrogen + chlorine → hydrogen chloride
The student must check the hazard information for all substances because each chemical has specific risks. Chlorine is toxic and can cause severe respiratory irritation; hydrogen is highly flammable and can form explosive mixtures with air; hydrogen chloride is corrosive and releases irritating vapours. Knowing these hazards allows the student to choose appropriate protective equipment, ventilation and handling procedures, thereby preventing injury or damage.
The student must check the hazard information for all substances because each chemical has specific risks. Chlorine is toxic and can cause severe respiratory irritation; hydrogen is highly flammable and can form explosive mixtures with air; hydrogen chloride is corrosive and releases irritating vapours. Knowing these hazards allows the student to choose appropriate protective equipment, ventilation and handling procedures, thereby preventing injury or damage.
Examiner tips
- Write the correct word equation first; it earns 1 mark. Explain that hazard data identifies risks – 1 mark. State that this knowledge lets the student take precautions – 1 mark. Give a specific hazard of one substance – 1 mark. Use UK spelling and correct terminology.
- common_mistakes
- :
- Writing a chemical equation instead of a word equation. Omitting a specific hazard or giving a general statement. Using American spelling (e.g., ‘colour’ instead of ‘colour’).
Mark scheme (4 marks)
- Correct word equation: hydrogen + chlorine → hydrogen chloride
- Hazard information identifies risks/dangers associated with the substances
- So that the student can take appropriate precautions / use correct safety measures
- Reference to a specific hazard of any named substance (e.g. chlorine is toxic/poisonous, hydrogen is flammable, hydrogen chloride is corrosive/toxic)
Key terms in this question
word equation · hazard information
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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