Page 215 - ICSE Chemistry 8

When the gas rises through the dough, spaces are formed and the dough becomes porous thus
making cakes and bread light, so and spongy.
• Fire ex nguishers: Carbon dioxide is used in fi re ex nguishers because it is neither combus ble
nor supports combus on.
• Photosynthesis: Green plants use carbon dioxide to prepare food by photosynthesis.

Activity 9.9

Aim: To observe the use of carbon dioxide in cooking
Materials required: A bowl, some wheat fl our, some baking soda, some water, some vinegar

Procedure
• Take some wheat fl our and add a tablespoon of baking soda to the fl our.
• Add water and knead properly to prepare a dough in a way that baking soda is distributed evenly.
• Mark the height of the dough.
• Now add a li le vinegar to the dough and mix it properly.
• Leave the dough for about 7 to 9 minutes.

Observa on: You will observe that the dough rises.
Conclusion: We conclude that baking soda consists of carbonate, and ace c acid is present in vinegar. The
carbonate reacts with the acid to produce carbon dioxide. The carbon dioxide formed escapes through
the pores in the dough which causes the dough to rise.

Greenhouse Effect

The trapping of solar heat in the earth's lower atmosphere is known as greenhouse eff ect. Greenhouse
gases present in the earth’s atmosphere absorb the infrared radia ons and keep the earth’s surface warm.
Carbon dioxide is a greenhouse gas which absorbs infrared radia ons.
The sun’s rays on reaching the atmosphere pass through it to the earth’s surface. Some heat energy carried
by the sun’s rays keeps the planet warm. Some of this heat is radiated back through the atmosphere to
space. While some heat is absorbed by carbon dioxide as it travels back through the atmosphere. This
trapped heat keeps the planet warm thus making it a place where life can thrive.

In addi on to carbon dioxide, methane and water vapour also contribute to greenhouse eff ect.

Today, due to human ac vi es such as burning of fossil fuels and using huge numbers of vehicles, large
amount of carbon dioxide is released into the atmosphere. The extra carbon dioxide produced due to
human ac vi es is adding to the increase in global temperature which causes global warming.

Global Warming

Global warming is defi ned as the increase in the average temperature of the earth’s atmosphere. Global
warming aff ects the weather pa erns on earth and causes climate change. Climate change further results
in increased rainfall, higher sea levels, and severe droughts and fl oods. This has also led to mel ng of
polar ice caps.

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