Grade 6 (age 11-12)

grade 6 Various Gases

Various Gases

The air we breathe looks like nothing, but it is really a mix of gases like nitrogen, oxygen, and carbon dioxide. Nitrogen makes up about 78 percent and oxygen, which we breathe, about 21 percent. Gases are made of tiny particles: they move faster when warmer and the pressure rises when they are packed into a smaller space. Pick oxygen, carbon dioxide, or nitrogen, then change temperature and volume and the particles come into view.

Gases Are Invisible

Temperature50

💨 Motion of Gas Particles

①Like air, invisible particles are constantly moving

②Higher temperature → particles move faster

③Particles collide and spread in all directions

④Slider numbers are a relative scale, not °C or mL.

Gases in the Air

🌬️ Composition of Air

①Air is a mixture of many gases

②Nitrogen is the most (~78%)

③Oxygen is ~21%, needed for respiration

④CO₂ is small but vital for photosynthesis. It makes limewater cloudy.

Volume & Pressure

Volume80

💡 Volume vs Pressure

①Smaller gas volume → higher pressure

②Pressing a sealed syringe pushes back harder

③Same gas in smaller space → more particle collisions

Summary

Composition of Air

Air = N₂(78%) + O₂(21%) + Others(1%)

Air is a mixture of gases

Properties of Gases

Temp ↑ → particle motion ↑ / Volume ↓ → pressure ↑

Temperature and volume govern gas behavior

🎯 Key Points

①Most of air is N₂ (78%); O₂ is ~21%

②O₂: respiration and combustion

③CO₂: photosynthesis, makes limewater cloudy

④Smaller volume → higher pressure

⑤Higher temp → faster gas particles

Examples and Unit Test

Example 1

Which gas makes up about 78% of the air, and which about 21%?

Air is a mixture of several gases.

Nitrogen is the most abundant at about 78%, followed by oxygen at about 21%.

▸ Nitrogen (~78%), oxygen (~21%)

Air = 78% nitrogen + 21% oxygen + 1% other. Oxygen is used for breathing and burning.

Example 2

You block a syringe and push the plunger, shrinking the gas volume inside. What happens to the pressure, and why?

As the volume shrinks, the same number of gas particles crowd into a smaller space.

The particles hit the walls more often, so the pressure rises.

▸ The pressure rises (more particle collisions in a smaller space)

Volume down → pressure up. A higher temperature makes particles move faster.

Unit-test style

Which statement about gases is correct?

①Oxygen makes up the largest fraction of the air

②Reducing a gas's volume raises its pressure

③Carbon dioxide makes limewater clear

④A higher temperature makes gas particles move slower

⑤Oxygen is used as a raw material for photosynthesis

▸ ② Reducing a gas's volume raises its pressure

When the volume shrinks, particles collide with the walls more often in the smaller space, so pressure rises.

Nitrogen is the most abundant in air (①), carbon dioxide makes limewater cloudy (③), a higher temperature makes particles move faster (④), and the raw material for photosynthesis is carbon dioxide (⑤).

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