iGCSE Chemistry (0620) Core:10.3 Air quality and climate: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
When heated, copper reacts with the oxygen in the air to form solid copper(II) oxide, removing the oxygen from the gas mixture. Clean, dry air is about 21% oxygen and about 79% nitrogen plus other inert gases that do not react with copper. So starting with 100cm³ of air, the 21cm³ of oxygen gets used up and locked into the solid oxide, leaving behind the 79cm³ of unreactive gases. When all the remaining gas is pushed into the syringe, it reads 79cm³ exactly.
▶️ Answer/Explanation
Detailed solution:
The reaction shown is the photosynthesis equation: carbon dioxide and water react, using sunlight energy and chlorophyll, to form glucose and oxygen. This is how plants make their food. Combustion uses oxygen to burn a fuel, decomposition breaks things down, and displacement involves replacing an element in a compound.
▶️ Answer/Explanation
Detailed solution:
Clean, dry air is approximately 78% nitrogen. That’s well over 30%. Oxygen makes up about 21%, which is less than 30%. Argon is about 0.9%, and carbon dioxide is only about 0.04%. So nitrogen is the only gas listed that exceeds 30%.