Atmospheric Gases: Composition, Uses, and Tests

Gases in the Atmosphere

• The air we breathe is a mixture of gases, roughly composed of:
  • 78.1% Nitrogen
  • 20.96% Oxygen
  • 0.9% Argon
  • 0.04% Carbon dioxide
  • Less than 0.01% other gases
• Despite its low concentration, the level of carbon dioxide in the atmosphere has drastically increased since the beginning of the Industrial Age.

Uses of Gases

• Nitrogen is used in food packaging and fertilisers.
• Oxygen facilitates breathing and burning.
• Argon is utilized in lightbulbs.
• Carbon dioxide is found in fire extinguishers and fizzy drinks.

Gas Tests

• Performing a gas test can prove the presence of a gas.
• Nitrogen gas does not have a test due to it being quite unreactive.
• Testing for oxygen gas:
  • Place a glowing splint into a test tube of oxygen gas
  • The oxygen gas will relight the splint
• Testing for carbon dioxide gas:
  • Pour limewater into a test tube of the gas, stopper it, and shake
  • Carbon dioxide causes the limewater to turn cloudy
• Testing for hydrogen gas:
  • Place a glowing splint into a test tube of hydrogen gas
  • Hydrogen gas will burn with a 'pop' sound

The Fire Triangle

• A fire needs oxygen, heat, and fuel to occur.
• Removing one element of the fire triangle will extinguish the fire.
• Different types of fires can be put out safely by applying the fire triangle:
  • Chip pan/oil fire: Fire blanket or CO2 extinguisher removes oxygen
  • House fire/wood fire: Water removes heat
  • Forest fire: Removing fuel as a firebreak

Combustion

• Combustion = burning
• Fuels burn and react with oxygen to release energy
• Combustion of hydrogen:
  • Hydrogen reacts with oxygen to make water
  • Hydrogen burns with a 'pop' sound.
  • Word Equation: hydrogen + oxygen → water
  • Chemical Equation: H2 + O2 → H2O
• Combustion of carbon:
  • Carbon reacts with oxygen that creates either carbon dioxide or carbon monoxide
  • Complete vs. incomplete combustion depends on oxygen availability
• Complete combustion of carbon: Occurs with a plentiful oxygen supply, resulting in carbon dioxide
  • Word equation: Carbon + oxygen → carbon dioxide
  • Chemical equation: C + O2 → CO2
• Incomplete combustion of carbon: Occurs with a limited oxygen supply, resulting in carbon monoxide formation
  • Word equation: Carbon + oxygen → carbon monoxide
  • Chemical equation: C + O2 → CO
• Carbon monoxide is an odourless, colourless, and highly poisonous gas
• All houses should have a carbon monoxide detector near each source of combustion.

Respiration

• Glucose molecules are transported to every cell for respiration
• Chemical reaction occurs which converts chemical energy into kinetic and heat energy
• Word equation for respiration: glucose + oxygen → carbon dioxide + water
• The presence of carbon dioxide can be proved using limewater
• Carbon dioxide turns limewater cloudy.
• Water vapour converts to liquid when we breathe out on a cold day - "see our breath" or condensation

Photosynthesis

• Plants make their own food by converting sun energy to chemical energy
• The plant takes in carbon dioxide and water and converts it to oxygen and glucose
• Chlorophyll in the plant traps the sun's rays, which then allows for the reaction to take place
• Word equation for photosynthesis: carbon dioxide + water → glucose + oxygen
• Photosynthesis is important because it:
  • Makes carbohydrates
  • Makes oxygen
  • Uses up carbon dioxide
• Glucose is converted to starch, which can be tested for:
  • Iodine turns blue-black in the presence of starch

Carbohydrates

• Many food types contain carbohydrates.
• Carbohydrates:
  • Sugars
  • Starch
• Carbohydrates are compounds containing carbon, hydrogen, and oxygen.
• Carbohydrates can be identified via their ratio of hydrogen to oxygen atoms (2:1)
  • Glucose (C6H12O6)
  • Lactose (C12H22O11)
• Testing carbohydrates:
  • Sugars are soluble in water. Starch is insoluble
  • Iodine solution:
    • Brown to blue/black = starch present
    • Remains brown = sugars present
  • Benedict's test:
    • Turns from blue to brick-red when heated = sugars present
    • Sucrose is an exception, doesn't change colour of solution

Digestion

• Digestion is a series of chemical reactions for the body to use energy from food
• Glucose passes through the gut wall to the bloodstream, where it is taken to our cells for respiration
• Starch is a larger molecule that cannot pass through the gut wall on its own
• During digestion starch is broken down into glucose to pass through the gut wall/cells for respiration:
  • Amylase (enzyme/biological catalyst) in saliva
  • Hydrochloric acid in the stomach
• In lab experiments, amylase is used within visking tubing (represents the gut wall) to replicate the process:
  • Pores in the tubing are small enough to only permit smaller glucose molecules through
  • Effectiveness of amylase can be proved via Benedict's test to detect presence of sugars

Energy from Food

• Carbohydrates = source of energy
• Chemical energy gets converted into heat during combustion.
• Occurs during respiration, when carbohydrates react with oxygen to release energy
• Experiments can be set up to measure heat via burnt foods to test energy.

Fuels

• Fuel is a substance with stored chemical energy
• Energy is stored in chemical bonds through processes like photosynthesis.
• Fossil fuels:
  • Coal
  • Oil
  • Natural gas
• Fossil fuels come from decayed and fossilized plants and animals that lived millions of years ago
• Finite resource because they will eventually run out.
• Stored energy can be released by burning fossil fuels
• Electricity can come from the burning of coal and natural gas
• Fossil fuels contain burning, and produce carbon dioxide

The Carbon Cycle

• The carbon cycle involves the movement of carbon atoms on our planet.
• It shows the different forms of carbon and how it converts through essential chemical reactions.

The Greenhouse Effect

• The greenhouse effect = heat is trapped in the Earth's atmosphere by greenhouse gases
• Carbon dioxide is one of the greenhouse gases
• Natural process for sustaining life on Earth
• Increased use of fossil fuels and deforestation have increased carbon dioxide, leading to more trapped heat and increased global temperatures.
• Burning fossil fuels increases carbon dioxide, whereas plants can remove it through photosynthesis.

Learning Outcomes

• The atmosphere is a mixture of gases.
• Air is roughly 78% nitrogen, 21% oxygen, 1% argon, 0.04% carbon dioxide, and trace gases.
• Oxygen re-lights glowing splint.
• Carbon dioxide turns limewater milky.
• Draw the fire triangle
• The fire triangle is used to extinguish different types of fires.
• Combustion is another word for burning.
• Use word and chemical equations for hydrogen/carbon combustion.
• Respiration is the reaction when glucose reacts with oxygen, producing carbon dioxide and water.
• Respiration releases energy.
• Photosynthesis is the reaction in plants that produces oxygen and glucose.
• Glucose = starch in plants
• Oxygen:hydrogen ratio is 2:1 in carbohydrates.
• Sugars are soluble in water, whereas starch is insoluble.
• For starch:
  • lodine turns from brown to blue-black
• For sugar:
  • Benedict's solution turns blue to brick red when heated, except sucrose
• Carbohydrates = source of energy
• Glucose passes through the gut wall
• Digestion is the process to break starch into glucose molecules.
• Use amylase or hydrochloric acid to break down starch.
• Amylase an enzyme.
• Fuel has stored energy.
• Coal, oil, and natural gas are fossil fuels.
• Fossil fuels are a finite energy source.
• Fossil fuels produce carbon dioxide when burned.
• Describe greenhouse effect.
• Carbon dioxide/ greenhouse gasses trap heat
• Describe result of increase in carbon dioxide in last 150 years.

Explore the composition of air, including nitrogen, oxygen, argon, and carbon dioxide. Discover the various uses of these gases in industries like food packaging, lighting, and fire safety. Learn how to perform simple gas tests to identify oxygen and carbon dioxide.