2.24 understand the carbon dioxide is a greenhouse gas and may contribute to climate change

Gases in the atmosphere (such as carbon dioxide, methane, water vapour) act as natural insulators, trapping heat from the sun inside Earths atmosphere. This is because they absorb most of the heat that would normally be mediated out into space. They reradiate this trapped heat in all directions, including back towards Earth.

The level of carbon dioxide can increase due to many factors, some as a result of humans. For example, deforestation (fewer CO2 is removed by photosynthesis) and burning fossil fuels (CO2 that was 'locked' in these fuels is being released).

Although the Earth's temperature naturally varies (interglacial and glacial periods), there is reason to believe that extra CO2 has caused the average temperature to increase.

2.23 explain the uses of carbon dioxide in carbonating drinks and in fire extinguishers, in terms of its solubility and density

The stuff that makes your fizzy drinks fizzy is the carbon dioxide. As CO2 is slightly soluble in water and dissolves in drinks when user high pressure, a slightly acidic solutions forms due to the formation of carbonic acid. It eventually goes flat because, once you open the bottle, the CO2 is escaping (when it is flat, its all gone)

CO2 is more dense than air, this makes it perfect for fire extinguishers. The CO2 will sink onto flames and 'suffocate' them (stop the oxygen getting to the flames). As fire needs oxygen to burn, the fire will go out as no oxygen can get to it.

NOTE: CO2 fire extinguishers are only used when water extinguishers aren't safe. For example, when putting out an electrical fire.

2.22 describe the properties of carbon dioxide, limited to its solubility and density

Carbon dioxide is more dense than air (which is why it can be collected using the downward delivery method). It is also soluble in water at high pressure.

2.21 describe the formation of carbon dioxide from the thermal decomposition of metal carbonates such as copper(II) carbonate

The thermal decomposition (heating)  of metal carbonates will produce CO2 as, in thermal decomposition, the substance being heated will break down into simpler substances.

Method

- Put some copper(II) carbonate (its a green powder, if your wondering) into a test tube and insert a bung with a delivery tube at the top
- Clamp the test tube at a 90º angle and insert the delivery tube into another test tube (that is positioned vertically)
- Heat the copper(II) carbonate with a bunsen burner.

NOTE: Because CO2 is denser than air, the downward delivery method can be used.

Equations

Copper(II) carbonate ---> copper oxide + carbon dioxide

CuCO3(g) ---> CuO(s) + CO2(g)

2.20 describe the laboratory preparation of carbon dioxide from calcium carbonate and dilute hydrochloric acid

Dilute HCL will react with calcium carbonate (aka marble chips) to produce calcium chloride, water and carbon dioxide...

Method

- Put marble chips at the bottom of a flask
- Fill the flask with hydrochloric acid, it doesn't have to be full, just covering the marble chips
- immediately attach a bung with a delivery tube into an upturned test tube in water
- the carbon dioxide will collect in this test tube


Equations

hydrochloric acid + calcium carbonate ---> calcium chloride + water + carbon dioxide

2HCL(aq) + CaCO3(s) ---> CaCl2(aq) + H2O(l) + CO2(g)

2.19 describe the reactions of magnesium, carbon and sulphur with oxygen in air, and the acid-base character of the oxides

When anything is burnt, it reacts with oxygen in the air to form oxides (which can have wither acidic or basic character). 

Magnesium
When magnesium burns in air, it produces a bright white flame and a white powder is formed (this is magnesium oxide). Magnesium oxide is slightly alkali when dissolved in water.

The equation for the reaction (burning Mg in air) is 2Mg_(s) + O_2(g) ---> 2MgO_(s)

NOTE: This question often comes up in exams so make sure you know it!

Carbon
Carbon will only burn in air if it is very strongly heated. It burns with a yellowy-orangey flame and produces carbon dioxide (as a gas). Carbon dioxide is slightly acidic when dissolved in water.

The equation for the reaction (burning C in air) is C_(s) + O_2(g) ---> CO_2(g)

Sulfur
Sulphur burns (in air) with a pale blue flame and produces sulfur dioxide which is acidic when dissolved in water.

The equation for this reaction (burning S in air) is C_(s) + O_2(g) ---> SO_2(g)

2.18 describe the laboratory preparation of oxygen from hydrogen peroxide, using manganese(IV) oxide as a catalyst

Hydrogen peroxide will decompose to form oxygen and water. However, this process is very slow so manganese (IV) oxide is added to speed up the decomposition (this acts as a catalyst). The oxygen produced can be collected in two ways...

1. Over water...
- connect a delivery tube to bubble the gas into an upside-down measuring cylinder in a beaker/bowl full of water.

2. In a gas syringe...
- you can use a gas syringe to collect pretty much any gas... just connect it to the flask that the hydrogen peroxide is decomposing in.

NOTE: the equation for this reaction is 2H₂O_{2 (aq)} ---> 2H₂O _(l) + O_{2 (g)}

2.17 explain how experiments involving the reactions of elements such as copper, iron and phosphorus with air can be used to investigate the percentage by volume of oxygen in air

Copper

- When copper is heated, it reacts with oxygen in the air to make copper(II) oxide - this reaction uses up oxygen
- If you heat an excess of copper in a tube and pass it over two syringes, you can use the markers on the syringes to work out how much oxygen as been used up. Conclusion... if you start with 100cm³ of air, you should end up with around 80cm³ air once the reaction is finished (and cooled). This means that 20% of the air has gone, meaning 20% must be oxygen

Iron or phosphorus

Iron will react with oxygen to produce rust, this means iron will remove oxygen from the air.

Method...

- soak some iron wool in acetic acid (this acid will catalyse the reaction)
- push the iron wool at the bottom of a test tube and invert the tube into a beaker of water
- mark the level of the water in the tube at the beginning
- leave the experiment for a set amount of time (e.g. 1 hour)
- mark the level of water in the tube at the end of the experiment

Conclusion...

Over time, the level of the water will rise in the test tube. This is because the iron reacts with the oxygen in the air, making iron oxide (the water rises as it takes the place the oxygen took up).

To work out the percentage of air that is oxygen, mark the level of the water in the tube at the beginning and end of the experiment, then, fill up the tube to each mark and pour the contents into a measuring cylinder to find out the volume of air at the start and end. Using the difference between the start and end volumes, work out the % that has been used to (should be approx 20%).

Phosphorus - you can do a similar experiment with white phosphorus. White phosphorus smoulders in air to produce phosphorus oxide. Use the same calculation method as with iron.

2.16 recall the gases present in air and their approximate percentage by volume

78% nitrogen

21% oxygen

nearly 1% argon

0.04% carbon dioxide