Questions 1 - Oxygen and the oxides

Q1. In each of the processes, state whether carbon dioxide in the atmosphere increases, decreases or stays the same:

i. burning fossil fuel
ii. volcanic activity
iii. dissolving in oceans

Answer
Q1 i. Increases
ii. Increases
iii. Decreases - although the overall CO2 level in the world doesn't change, it is taken from the air into the ocean. Read the question!

Q2. The pie chart shows the composition of air today. Choose the correct option:

Gas x is:

a. chlorine

b. hydrogen

c. nitrogen

d. radon

Answer

Q2. Gas x is nitrogen. 

If you don't know this by heart, you can take an educated guess: 

- Chlorine is poisonous (so that can't be)

- Radon is radioactive (so that can't be either)

You're left with 2 options, nitrogen or hydrogen. Each gives you a 50% chance of getting the mark. So hopefully, you'd have ticked/crossed nitrogen :)

2.24 Understand that carbon dioxide is a greenhouse gas and may contribute to climate change.

Carbon dioxide, as mentioned above, is a greenhouse gas. This means it traps heat in the planet and stops the sun's rays being reflected away from the earth. Excess levels of carbon dioxide contribute to climate change, causing the earth to warm up at unnatural rates.

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

• It's used in fire extinguishers because it's denser than air and deprives the flame of oxygen, making it die down.
• Carbon dioxide is dissolved into fizzy drinks at high pressure, so there's bubbles when you drink it :)

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

• It is somewhat soluble in water, at a high pressure. If it's not at high pressure, it can be diluted in water but its pretty hard, and only a small amount will be diluted.

• It's denser than air - about 1.98 kg/m³ - so if you fill a balloon with it, it will fall faster than if you fill a balloon with air (it's cool, you should try it some time!)

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

When you heat a metal carbonate, it becomes carbon dioxide and a metal.

metal carbonate >> carbon dioxide + metal

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

Calcium carbonate + Hydrochloric acid → Calcium chloride + carbon dioxide + water

CaCO3 + HCl(aq) → CaCl + CO2 + H2O

2.19 Describe the reactions of magnesium, carbon and sulfur with oxygen in air, and the acid-base character of the oxides produced

Metal will form a metal oxide - BASIC
Non metal will form a non meal oxide - ACIDIC




Magnesium (metal):

• Take a rod of magnesium
• Put it in a bunsen burner flame
• BAM IT SPARKLES WITH A WHITE LIGHT DON'T LOOK DIRECTLY AT IT
• (the scientific way of saying that is it has a bright white flame)

You only need to watch the first minute and a half of this video to see the actual reaction, the rest is an explanation

Carbon (non metal):

• Put it in a super long spoony thing
• Heat it gently
• Put it in a gas jar with pure oxygen
• IT WILL GLOW RED AND LOOK LIKE LAVA

Sulphur (non metal):

• Put it in a super long spoony thing
• Heat it over a bunsen so it catches fire a bit
• Place the spoony thing into a gas jar with pure oxygen
• IT WILL GLOW BLUE

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

• Set up the apparatus shown in the video
• Add the catalyst (manganese(IV) oxide)
• Allow the oxygen to bubble into the gas jar
• Done ^_^

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

The elements mentioned above all react with air (copper, iron and phosphorus). You could set up the following experiment:

• Set up the apparatus shown in the video :)
• You must have a know volume of air, as shown
• Heat the copper bits evenly, and keep pressing down one syringe and then the other, so the air passes through the copper
• The oxygen will react with the copper to form copper oxide and will be 'taken away' from the air
• Keep repeating step 3 until the volume of air stops decreasing
• Turn off the bunsen burner (or put it aside) 
• Leave to cool for 5 minutes
• Measure final reading. The volume of air should have gone down. 
• Calculate the percentage of decrease in volume of air. This is the percentage of oxygen there was.

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

The air is made up of approximately

• 21% oxygen
• 78% Nitrogen
• 1% Other gases (including 0.9% argon and 0.037% carbon dioxide)