WaterCambridge IGCSE Chemistry: Flashcards
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What is the chemical test for the presence of water using anhydrous cobalt(II) chloride?
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- What is the chemical test for the presence of water using anhydrous cobalt(II) chloride?
- Anhydrous cobalt(II) chloride is blue. When water is present, it turns pink because it forms a hydrated complex with the water molecules.
- What is the chemical test for the presence of water using anhydrous copper(II) sulfate?
- Anhydrous copper(II) sulfate is white. When water is present, it turns blue because it forms a hydrated complex (CuSO₄·5H₂O) with the water molecules.
- How is the purity of water tested using melting point and boiling point?
- Pure water has a melting point of 0 °C and a boiling point of 100 °C. Impure water has a different melting point (lower) and boiling point (higher) than pure water.
- Why is distilled water used in practical chemistry rather than tap water?
- Distilled water is used because it contains fewer chemical impurities, ensuring that any reactions or results are not affected by unwanted dissolved substances.
- Name four substances that may be present in water from natural sources.
- Dissolved oxygen, metal compounds, plastics, sewage, harmful microbes, nitrates and phosphates from fertilisers.
- Which dissolved substances in water are beneficial and why?
- Dissolved oxygen is beneficial because it is essential for aquatic life. Some metal compounds are beneficial because they provide essential minerals.
- Explain why some metal compounds in water are potentially harmful.
- Some metal compounds are toxic to aquatic organisms and humans. They may accumulate in the body and cause poisoning.
- Why are plastics in water potentially harmful?
- Plastics can harm aquatic life by being ingested by animals, causing physical damage or blockages, and breaking down into microplastics that contaminate ecosystems.
- How does sewage in water pose a health risk?
- Sewage contains disease-causing microbes and pathogens that can cause serious illness or death if the water is consumed without treatment.
- Explain the problem caused by nitrates and phosphates in water.
- Nitrates and phosphates from fertilisers cause eutrophication. They cause excessive algal growth, which depletes dissolved oxygen when the algae decompose, leading to deoxygenation of the water and death of aquatic life.
- What does the sedimentation and filtration stage remove from domestic water?
- Sedimentation and filtration remove solid particles and suspended impurities from the water.
- Why is carbon used in the treatment of domestic water supply?
- Carbon (activated carbon) removes tastes and odours from the water by adsorption.
- What is the purpose of chlorination in domestic water treatment?
- Chlorination kills harmful microbes and pathogens in the water, making it safe to drink.
- Describe the three main stages of domestic water treatment in order.
- Sedimentation and filtration (remove solids). 2. Carbon treatment (remove tastes and odours). 3. Chlorination (kill microbes).
- Name the two chemical reagents used to test for the presence of water.
- Anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate.