1. Experimental Techniques
Collection of gases
The method used for collecting a gas depends on two factors:
EXAM TIP: Air has a molecular mass of approximately 28 or 29.
Upward delivery of gas: For gases which are soluble in water & less dense than air e.g. hydrogen
Downward delivery of gas: For gases which are soluble in water & more dense than air e.g. carbon dioxide
Displacement of water: Not for gases which are soluble in water e.g. NOT FOR ammonia and sulfur dioxide
Drying of gases
Drying agents are used to remove moisture from gases.
Neutral gases: hydrogen, oxygen
Acidic gases: chlorine, hydrogen chloride, sulfur dioxide
Alkaline gases: ammonia
Pass gas through fused calcium oxide: For drying neutral and alkaline gases. NOT FOR acidic gases.
Concentrated sulfuric acid: For drying neutral and acidic gases. NOT FOR alkaline gases.
Anyhydrous calcium chloride: For drying neutral, acidic and alkaline gases.
EXAM TIP: Anhydrous calcium chloride cannot be used to dry ammonia gas.
Apparatus
Stopwatch: For measuring time to the nearest 0.01s
Electronic balance: For measuring mass to the nearest 0.01g
Thermometer: For measuring temperature to the nearest 0.5°C
Gas syringe: For measuring volume of gas to the nearest 0.5cm3
Measuring cylinder: For measuring volume of solution to the nearest 0.5cm3
Burette: For measuring variable & accurate volume of solution to the nearest 0.01cm3
Pipette: For measuring fixed & accurate volume of solution (25.0cm3)
The method used for collecting a gas depends on two factors:
- Molecular mass of as or density compared to air
- Solubility of gas in water
EXAM TIP: Air has a molecular mass of approximately 28 or 29.
Upward delivery of gas: For gases which are soluble in water & less dense than air e.g. hydrogen
Downward delivery of gas: For gases which are soluble in water & more dense than air e.g. carbon dioxide
Displacement of water: Not for gases which are soluble in water e.g. NOT FOR ammonia and sulfur dioxide
Drying of gases
Drying agents are used to remove moisture from gases.
Neutral gases: hydrogen, oxygen
Acidic gases: chlorine, hydrogen chloride, sulfur dioxide
Alkaline gases: ammonia
Pass gas through fused calcium oxide: For drying neutral and alkaline gases. NOT FOR acidic gases.
Concentrated sulfuric acid: For drying neutral and acidic gases. NOT FOR alkaline gases.
Anyhydrous calcium chloride: For drying neutral, acidic and alkaline gases.
EXAM TIP: Anhydrous calcium chloride cannot be used to dry ammonia gas.
Apparatus
Stopwatch: For measuring time to the nearest 0.01s
Electronic balance: For measuring mass to the nearest 0.01g
Thermometer: For measuring temperature to the nearest 0.5°C
Gas syringe: For measuring volume of gas to the nearest 0.5cm3
Measuring cylinder: For measuring volume of solution to the nearest 0.5cm3
Burette: For measuring variable & accurate volume of solution to the nearest 0.01cm3
Pipette: For measuring fixed & accurate volume of solution (25.0cm3)
