Why is water vapour left out of the percentages for dry air?

Its amount changes from place to place and day to day.

What gases did early volcanoes release?

Carbon dioxide (mostly), water vapour and nitrogen, with almost no oxygen.

How did the oceans form?

The Earth cooled and water vapour condensed into liquid water that fell as rain.

Name two ways carbon dioxide was removed from the early atmosphere.

Dissolving in the oceans, and being locked up in sedimentary rocks, shells and fossil fuels.

Which process added oxygen to the atmosphere?

Photosynthesis by algae and plants.

Write the word equation for photosynthesis.

Carbon dioxide + water → glucose + oxygen.

What happens to copper heated in air?

It reacts with oxygen and turns from orange-brown to black copper oxide.

Why must the apparatus cool before the final gas volume is read?

A hot gas takes up more volume, so a hot reading would be too large.

Composition of the atmosphereIB MYP Chemistry: Flashcards

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Question

What percentage of dry air is nitrogen?

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What percentage of dry air is nitrogen?: About 78%.
What percentage of dry air is oxygen?: About 21%.
What percentage of dry air is argon?: About 0.9% (less than 1%).
What percentage of the air is carbon dioxide?: About 0.04%.
Why is water vapour left out of the percentages for dry air?: Its amount changes from place to place and day to day.
Which gas is the most abundant in the air?: Nitrogen.
What gases did early volcanoes release?: Carbon dioxide (mostly), water vapour and nitrogen, with almost no oxygen.
How did the oceans form?: The Earth cooled and water vapour condensed into liquid water that fell as rain.
Name two ways carbon dioxide was removed from the early atmosphere.: Dissolving in the oceans, and being locked up in sedimentary rocks, shells and fossil fuels.
Which process added oxygen to the atmosphere?: Photosynthesis by algae and plants.
Write the word equation for photosynthesis.: Carbon dioxide + water → glucose + oxygen.
Calculate the volume of oxygen in 10 dm³ of dry air.: 21 ÷ 100 × 10 = 2.1 dm³.
What happens to copper heated in air?: It reacts with oxygen and turns from orange-brown to black copper oxide.
Why must the apparatus cool before the final gas volume is read?: A hot gas takes up more volume, so a hot reading would be too large.

Exam questions on Composition of the atmosphere

A diving equipment supplier in Cape Town fills cylinders with compressed dry air. Dry air is a mixture of gases. It is mainly nitrogen and oxygen, with small amounts of argon and carbon dioxide.
The gases other than nitrogen and oxygen make up about 1% of dry air. Name the gas that is the largest part of this 1%, and state the name of the group of elements to which it belongs.2 marks
A student in Mumbai measures the percentage of oxygen in air. She puts 100 cm³ of air in a gas syringe that is connected through a tube of heated copper turnings to a second, empty syringe. She pushes the air slowly back and forth over the hot copper until the volume stops changing. When the apparatus has cooled to room temperature, the volume of gas left is 79 cm³.
Use the results to calculate the percentage of oxygen in the air sample.2 marks
Scientists believe that 4 billion years ago the atmosphere of the Earth contained mostly carbon dioxide, with water vapour and nitrogen released by volcanoes, and almost no oxygen. Today, carbon dioxide makes up about 0.04% of the air and oxygen makes up about 21%.
Describe how the percentage of carbon dioxide in the atmosphere decreased as the Earth cooled.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).