In this unit we will:
- Understand that a gas consists of particles and be able to explain its properties.
- Recognize the relationship between pressure and the volume of a gas as being a change in the distance between particles.
- Identify techniques for producing oxygen and carbon dioxide and understand their properties.
- Investigate situations in which gases are used in everyday life and be able to explain such cases in relationship to the properties of these gases.
Lesson 1: Why does water rise in a glass?
Facts:
- At first, the flame heats the air inside the container and this hot air expands quickly.
- Some of the expanding air escapes from under the glass where you might have seen some bubbles.
- When the flame has used all of the oxygen it goes out (it is extinguished).
- The air in the container cools and cooler air contracts and takes up less space.
- That contraction creates lower pressure in the container.
- The outside air pressure is now higher than the pressure inside the glass.
- The outside air pressure pushes down on the water in the dish.
- The outside air pushes water into the container until the pressure is equalized inside and outside the container.
- The water stops rising when that pressure equalization is reached.
- A common misconception is that the consumption of oxygen by the flame in the container is the reason the water is rising.
- There would be a tiny rise in the water from the flame using up oxygen, but it’s extremely small compared to the actual reason.
- If it were just the consumption of oxygen by the flame causing the water to rise, then the water would rise imperceptibly at a steady rate as the oxygen was consumed.
- What actually happens is that the water level rises almost all at once and pretty much after the flame went out.
Lesson 2: Why do balloons burst?
Facts:
- The air around us is made of different gases.
- These gases are made of gas particles.
- Gas particles exert pressure on the walls of the container in which the gas is filled.
- When more air is forced into an object, like a balloon, we say it is being inflated.
- As the balloon is inflated more and more air is forced inside.
- As more air goes in, the gas particles are forced closer and closer together.
- This causes the pressure inside the balloon to increase.
- This increase in air pressure exerts pressure on the rubber walls of the balloon and the size of the balloon increases.
- Another way of saying this is that the volume of the balloon increases.
- The expansion is due to the elasticity of rubber.
- As more and more air is forced into the balloon the gas particles get closer and closer together and the pressure builds up inside.
- Eventually the rubber skin of the balloon expands to its maximum limits.
- If we blow again, the balloon cannot expand any further.
- The volume of the balloon is full and its volume can grow no bigger.
- The gas particles are very close together.
- The air that we blow in next also needs space so the balloon bursts.
Lesson 3: Can you make carbon dioxide gas?
Facts:
- When a human breaths in, one of the gases inhaled is oxygen.
- This enters the bloodstream and is delivered to all the cells of the body.
- The cells then make carbon dioxide gas and humans breathe this gas out.
- Humans are very good at making carbon dioxide. However, it is also possible to manufacture carbon dioxide by mixing an acid (vinegar) with a carbonate (baking soda).
- All living things are made of carbon.
- The chemical symbol for carbon is C.
- Carbon is in our bodies, and in the air, in the form of carbon dioxide.
- The chemical formula for carbon dioxide is CO2.
- Plants use carbon dioxide from the air to make their food.
- When humans and animals eat plants the carbon is transferred into the consumer.
- When one animal eats another the carbon is transferred again to the secondary consumer.
- When we breathe out, some of the carbon inside us is released back into the atmosphere as carbon dioxide.
- When animals die carbon is released into the soil where most of it is trapped.
- Over millions of years some of the trapped carbon in the soil will change into the fossil fuels coal and oil and maybe even into diamonds.
- A lot of carbon is trapped at the bottom of the world’s oceans. We call this a carbon sink.
- As humans burn fossil fuels carbon is released back into the atmosphere.
- As humans cut down forests less carbon is absorbed by the trees.
- This extra carbon in the atmosphere causes the Earth to heat rapidly causing climate change.
- If humans do not restore the balance in the carbon cycle the Earth will continue to get hotter and hotter.
Lesson 4: Can you show that air consists of invisible gases?
Facts:
- Everything in the universe is made of energy or matter.
- Matter takes up space.
- Matter can be a solid, liquid or a gas.
- The air around us consists of many different gases and air is a gas itself.
- The main gases in the air are nitrogen, oxygen and carbon dioxide.
- Helium is also a gas.
- We cannot smell these gases because they are odorless.
- We cannot see these gases because they are invisible.
- However, we can conduct experiments to prove that these gases exist.
- A bubble is a thin layer of soap with air trapped inside.
- If you blow bubbles into a tank they will fall to the bottom of the tank.
- Vinegar and baking soda can be mixed together to create carbon dioxide.
- Carbon dioxide gas is heavier than air.
- If you make carbon dioxide in a tank it will stay at the bottom of the tank because it’s heavier than air.
- Bubbles can float on top of a layer of carbon dioxide in a tank.
- Helium is lighter than air.
- If you fill a balloon with helium gas it will rise upwards.
Lesson 5: Can you get a boiled egg into a bottle?
Facts:
- At the beginning of the experiment the air pressure is the same both outside, and inside, the bottle.
- If you try to push the egg into the bottle it will get crushed and only some of it will go inside.
- When you place the boiled egg over the bottle opening, it creates a seal.
- The seal stops air getting into, or out of, the bottle.
- The fire inside the bottle heats the air.
- Hot air expands rapidly.
- The egg vibrates as the hot expanded air rushes out of the bottle past the egg.
- As the hot air leaves the bottle the amount of air in the bottle is reduced.
- Eventually, enough hot air leaves the bottle so that the the air pressure is the same both outside, and inside, the bottle again.
- Meanwhile, the fire inside the bottle needs oxygen to burn.
- As the fire burns it consumes the oxygen inside the glass and once all the oxygen is consumed the fire is extinguished.
- As there is now no heat from the fire, the air inside the glass cools rapidly.
- The cooled air contracts so that the particles of gas are less active and so the air pressure is lowered.
- Meanwhile, the air outside the bottle is still exerting the same amount of pressure.
- As the air pressure is now lower inside the bottle than outside the bottle, the egg is pushed into the bottle by the outside air pressure.
- When the seal created by the egg is broken, air from outside the bottle rushes in.
- At the end of the experiment the air pressure is the same again both outside, and inside, the bottle.
- Some of the paper in the bottle isn’t burnt because once the oxygen was consumed the fire is extinguished.
Lesson 6: Can you crush a plastic bottle without touching it?
Facts:
- We are surrounded by air and air is matter.
- Air is also a gas. It consists of particles of different gases including nitrogen, oxygen and carbon dioxide.
- Air is invisible but it has weight and mass and so it can exert pressure.
- At the beginning of the experiment the bottle looks empty but actually it is full of air.
- Steam is a gas. It is water in the gas phase.
- When the boiling hot water was poured into the bottle the steam pushed some of the air out.
- At the same time the air above the water surface was heated and hence expanded.
- This also pushed some of the air out so that the amount of air inside the bottle was reduced.
- When the lid was placed on to the bottle air could not get back into the bottle.
- Finally, when the cold water was poured over the bottle the steam condensed back into water and the air cooled and contracted.
- As there was now less particles of gas (steam) in the bottle the air pressure inside the bottle was lowered.
- As the air pressure inside the bottle fell significantly below the pressure exerted by the air on the outside, the walls were crushed inwards.
- Air is used in car and bicycle tires as it exerts a pressure on the tire walls.
- The air absorbs any shocks when we ride over bumps and makes the ride smoother and more comfortable.
Lesson 7: Can you put a fire out with carbon dioxide CO2?
Facts:
- The chemical symbol for carbon dioxide gas is CO2.
- We can't smell carbon dioxide gas because it's odorless.
- We can't see carbon dioxide gas because it's colorless.
- Carbon dioxide gas makes up about 0.037 % of the air.
- Carbon dioxide gas has many practical uses in real life.
- For instance, it can be used to extinguish fires.
- This is possible because fires need oxygen to burn.
- Carbon dioxide is also heavier than air.
- This is why when you create the carbon dioxide gas the particles don’t escape from the top of the cylinder.
- When you pour the invisible carbon dioxide out of the cylinder it flows down over the candle depriving the flames of oxygen.
- As the carbon dioxide is heavier than air it takes the place of the air.
- This means there is no oxygen and this is what puts the candles out.
- This is why many fire extinguishers are filled with carbon dioxide.
Lesson 8: Can you make oxygen?
Facts:
- The chemical symbol for oxygen gas is O2.
- We can't smell oxygen because it’s odorless.
- We can't see oxygen because it’s colorless.
- Oxygen makes up about 21 % of the atmosphere.
- We need oxygen to breath. Without oxygen all humans would die.
- Oxygen is the gas needed for life. All animals breathe it too.
- Even creatures living in the sea need oxygen to breathe.
- They have gills that are able to remove oxygen from the water.
- Plants are very good at making oxygen.
- They do so by a process known as photosynthesis.
- Photosynthesis is when plants use sunlight, water, and CO2 to make food and oxygen.
- We can make oxygen by adding hydrogen peroxide to yeast.
- Oxygen has many practical uses in real life.
- For instance, it can be used to help sick people to breathe more easily.
Lesson 9: What are the properties of oxygen?
Facts:
- We breathe in air about 17,000 times a day.
- About 21% of the air we breathe is oxygen.
- Our brains, bones, lungs, blood and heart work together to sustain our lives by delivering oxygen to tissues throughout our bodies.
- Most of the cells of our body need oxygen because it’s one of the key ingredients of aerobic respiration.
- For oxygen to reach the cells in our body it needs a transportation network.
- We have 20 trillion red blood cells traveling around our body.
- Each red blood cell has about 270 million oxygen binding molecules of hemoglobin.
- The oxygen binds to these molecules and is carried around the body by the red blood cells.
- The scarlet colour of our blood is caused by this hemoglobin.
- The body breaks down food that we eat and converts it into iron.
- Iron is used to make hemoglobin inside our bones.
- Our bodies make 2.5 million red blood cells per second.
- Our kidneys regulate the production of red blood cells.
- Actually, our breathing begins in the brain.
- The brain tells the muscles in the diaphragm and ribs to contract.
- This increases the size of the lungs and reduces the air pressure inside.
- Air then rushes inside.
- Our lungs are full of millions of tiny balloon like projections called alveoli.
- These increase the contact area between the air and the red blood cells to around 100m2
- The alveoli allow oxygen to be collected by the red blood cells.
- Then, the oxygen carrying red blood cells are carried by our blood throughout our bodies in the cardiovascular system.
- They deliver the oxygen to all the cells of our body.
- The cardiovascular system is a massive network of blood vessels which if you laid out in one long straight line would wrap around the Earth several times.
- Our hearts pump 1000 times a day to move our blood carrying oxygen around the body.
- Without oxygen our bodies would quickly die.
Lesson 10: Can you make hydrogen H2 gas?
Facts:
- Hydrogen gas can be made from vinegar and magnesium.
- The chemical symbol for hydrogen is H2
- It has no smell because it is odorless.
- We cannot see it because it is colorless.
- It is explosive because it is a combustible gas.
- Hydrogen is not poisonous.
- It is also fifteen times lighter than air.
- It is so light that when you produce it on Earth it rises straight up into space where it is dispersed.
- This is why you rarely find hydrogen on Earth.
- However, sometimes hydrogen is naturally produced in the eruption of volcanoes, in gas releases from fumaroles (cracks in the Earth’s crust) and in oilfields.
- Hydrogen also exists in other states combined with other elements.
- For instance water is made from hydrogen combined with oxygen.
- We can use an apparatus called an electrolyzer to separate the oxygen from the hydrogen.
- To extract the hydrogen from water would take a great deal of energy so it’s a very expensive process.
- This is why we say hydrogen is not a primary energy source.
- Hydrogen is an energy carrier as it is not found directly in nature.
- There are many different ways to make hydrogen.
- Algae can produce hydrogen by using the light of the sun.