IB MYP Chemistry : Types of chemical reaction – uses of salts Practice Question

Question  (17 marks) – Comparing De-icing Salts

Background:

A new company is looking to provide a local community with a better de-icer for roads. You are provided with the following salts and asked to determine which will be the best one for de-icing roads:

• Lithium chloride (LiCl)
• Potassium chloride (KCl)
• Magnesium chloride (MgCl₂)
• Calcium chloride (CaCl₂)
• Strontium chloride (SrCl₂)

a. (1 mark) The image below shows a bottle of strontium chloride, SrCl₂. Select the hazard represented by this symbol:

▶️ Answer & Explanation

Correct Answer: Toxic

Explanation:

• The skull-and-crossbones symbol specifically indicates acute toxicity (harmful if swallowed/inhaled)
• Strontium chloride is classified as toxic with LD₅₀ = 1473 mg/kg (oral, rat)
• This differs from:
  • Corrosive (⚠️): Causes skin burns
  • Flammable (🔥): Catches fire easily
  • Radioactive (☢️): Emits radiation

b. (16 marks) Design an experiment to investigate which salt would be the best de-icer for roads. In your answer, you should include:

1. The independent, dependent and control variables
2. A list of equipment you will use
3. The method you will follow
4. Details of measurements you will take to collect sufficient data
5. Any safety precautions you need to take

▶️ Answer & Explanation

Component	Details	Marks
Variables	• Independent: Type of chloride salt (5 specified) • Dependent: Mass of ice melted OR time to melt fixed mass • Control: Ice mass (e.g., 100g), ambient temperature, salt mass (e.g., 10g), container type	4
Equipment	• Digital balance (±0.01g precision) • Thermometer (±0.5°C) • Stopwatch • 5 identical containers • Measuring cylinder • Safety goggles & gloves	3
Method	1. Prepare 5 containers with equal ice masses (100g ±1g) 2. Add 10g of each salt to separate containers 3. Start timer and record temperature every minute 4. Measure melted water mass every 5 minutes 5. Continue until all ice melts or 1 hour elapses 6. Repeat for reliability (3 trials per salt)	4
Measurements	• Initial/final ice masses (to 0.01g) • Time to complete melting • Temperature changes (minute intervals) • Calculate melting rate (g/min) • Record observations (e.g., bubbling, residue)	3
Safety	• Wear goggles (salt solutions irritate eyes) • Use gloves (toxic/corrosive salts) • Work in ventilated area (chlorine gas risk) • Clean spills immediately (slippery surfaces) • Emergency eye wash available	2

Key Evaluation Points:

• Fair Testing: All salts tested under identical conditions (mass, temperature, container)
• Quantitative Data: Precise measurements enable rate calculations
• Reliability: Multiple trials reduce random errors
• Real-World Relevance: Simulates road de-icing conditions