Gases in the atmosphere

What are the approx percentages by volume of the 4 most abundant gases in the atmosphere?

Nitrogen: 78%
Oxygen: 21%
Argon: 0.9%
Carbon dioxide: 0.04%

Using a metal (e.g IRON) to determine the % by volume of oxygen in air.
What are the conditions for iron to rust? What is its chemical name?

• Iron is the only element to RUST, others OXIDISE (they both are reacting with oxygen)

• Iron only rusts if WET and OXYGEN is present. If there is oxygen but it is not wet, iron won't react/rust.

• Chemical name for rust: hydrated iron (III) oxide

What is the chemical and word equation for the reaction between iron and oxygen?

Chemical: 4Fe(s) + 3O2(g) + 2H2O(l) ~> 2Fe2O3 • H2O(s)
Word: Iron + Oxygen + Water ~> Hydrated iron (III) oxide

Calculation of O2%

Volume of oxygen used (initial reading - final reading)
————————————————————————————————— x 100
Volume of air at the start (total burette volume - initial burette reading, lo que ocupa el agua en el burette).

Method for calculating % of O2 in air using iron?

• Place WET iron fillings at the end of a burette (accurate way to measure volume) (use Vaseline if iron fillings do not stick).

• Use a clamp to hold the bufete vertically in the trough (tub like apparatus to hold water) of water.

• Measure and note the starting height of water level in the burette.

• Leave apparatus for weeks.

• Measure the final height of the water level in the burette.

La ciencia behind esto:

• Iron fillings will react with the oxygen in the air to form hydrated iron (III) oxide
• Water rises and replaces the reacted oxygen.
  Why might the percentage of oxygen be lower than expected?

• Incomplete reaction: not all the oxygen in the air reacted with the wet iron because the person didn't leave enough time for the reaction to fully occur (e.g 2 days).

Explain how painting prevents the iron in car bodies from rusting (2).

Some car manufacturers use paint containing tiny zinc particles. Explain how particles of zinc prevent iron in car bodies from rusting even when this paint is scratched (2).

• Paint provides a barrier/forms a coating

• Prevents water/oxygen reacting with the iron.

• Zinc is more reactive/higher in the reactivity series than iron.

• Zinc will oxidise/react before/instead of iron.
  ZINC DOES NOT RUST.

Using a metal (e.g COPPER) to determine the % by volume of oxygen in air.
What is the difference between using copper and iron to investigate this?

Difference between using copper and iron is the apparatus. Copper uses 2 glass syringes and a bunsen burner to heat up iron instead of a burette placed in the trough (tub like apparatus to hold water) of water.

Heating up to speed up oxidation/reaction so it is more vigorous. If not heated copper reacts very slowly and forms a thin layer of copper oxide, which acts as a protective barrier, preventing further oxidation of the underlying copper.

Using a non-metal (e.g PHOSPHORUS) to determine the % by volume of oxygen in air.
Method?

• Add phosphorus onto an evaporating dish and place it on a trough of water making sure it's floating (so that the flame is not put out).

• Cover this with a bell jar/glass tube

• Remove bung and record the initial water level.

• Ignite the phosphorus using a candle (and quickly place back the bung).

• Leave apparatus for several days until all white fumes have disappeared and the water level stops rising.

• Measure the final water level in the jar/tube.

Give a reason why the bung needs to be quickly replaced back

Burning phosphorus gives off a poisonous gas.

How does it work? Ciencia behind this.

After several days, the water will rise up the bell jar and reach a constant level as the phosphorus will react with the oxygen in the air in order to burn.
The water level will rise to replace the volume of oxygen lost during this reaction.

What is combustion? What is a characteristic of combustion?

The process of burning something. All combustion reactions involve a chemical change in which oxygen reacts with element or compounds to produce oxides.

Combustion reactions give out heat, so they will be exothermic reactions.

Describe the combustion of magnesium + equations

Intense white flame — White powder produced (magnesium oxide)

Magnesium + oxygen ~> magnesium oxide
2Mg(s) + O2(g) ~> 2MgO(s)

REMEMBER STATE SYMBOLS

Describe the combustion of hydrogen + equations

Exothermic reaction — produces water
Test for hydrogen: a lit splint makes a squeaky pop sound.

Hydrogen + oxygen ~> water
2H2(g) + O2(g) ~> 2H2O(l)

Describe the combustion of sulfur + equations

Blue flame — colourless poisonous gas produced

Sulfur + oxygen ~> sulfur dioxide
S(s) + O2 ~> SO2(g)

What is thermal decomposition?

The breaking down with heat.
The breaking down of a substance by heating

Thermal decomposition of metal carbonates

Metal carbonate → metal oxide + carbon dioxide

Thermal decomposition of copper(III) carbonate equation + observations. From MEMORY

Copper(III) carbonate → copper oxide + carbon dioxide
CuCO3 → CuO + CO2

Colour change from green (copper(III) carbonate) black (copper oxide)

Equations for thermal decomposition of magnesium carbonate and calcium carbonate.

Magnesium carbonate → magnesium oxide + carbon dioxide
MgCO3 → MgO + CO2

Calcium carbonate → calcium oxide + carbon dioxide
CaCO3 → CaO + CO2

How can we test if it is CO2 produced?

Using limewater. If CO2 is bubbled through limewater, it turns milky/cloudy white.

What is the greenhouse effect?

The warming of the Earth's surface due to greenhouse gases capturing and re-emitting heat (energy) back to Earth.

What are greenhouse gases + examples? Why are they necessary?

A molecule that can absorb energy emitted by the sun.
Carbon dioxide, methane, water vapour, nitrous oxides, CFCs.
Greenhouse gases maintain temperatures on Earth high enough to support life.

What is the main reason why CO2 levels are increasing so much? Other factors?

Human-driven production of CO2.

• Burning of wood (deforestation) and fossil fuels: produce electricity.

• Deforestation + agriculture: changing forest land to agricultural land. Also causes less trees to convert CO2 into oxygen.

• Respiration of animals

• Thermal decomposition of carbonate rocks (a product is CO2). This occurs naturally in volcanic activity.

• Effect of acids in carbonates: when acids react with carbonate rocks they produce CO2. This naturally occurs when rainwater (slightly acidic due to dissolved CO2) reacts with carbonate rocks.

What are the consequences of increase levels of CO2?

• Leads to global warming which then leads to climate change.
• More extreme weather events (droughts, fires)
• Ice caps melting, rising sea levels and flooding.
• Species extinction. Destroyed habitats, acid rain (greenhouse gases like nitrogen oxides react with water vapour) kills ecosystems.
• Increase spread of disease (e.g malaria)

Difference between climate change and global warming

"Global warming" refers to the rise in global temperatures due mainly to the increasing concentrations of greenhouse gases in the atmosphere. "Climate change" refers to the increasing changes in the measures of climate over a long period of time - including precipitation, temperature, and wind patterns.