Gases in the atmosphere Flashcards
What percentage by volume is the air nitrogen?
78%
What percentage by volume is the air oxygen?
21%
What percentage by volume is the air Argon?
0.93%
What percentage by volume is the air carbon dioxide?
0.04%
What percentage by volume is the air inert gases, water vapour and pollutants?
0.03%
Describe the method which you could use to measure the percentage of oxygen in the air with copper
- assemble the equipment so that two gas syringes, one containing 100ml of air, the other none, facing one another are both connected to a tube containing copper powder by capillary tubes.
- make sure the area is sealed so that no air escapes and the test is accurate
- heat the tube containing the copper powder with a blue/ roaring flame, from different angles to ensure all copper is heated (uniform heating)
- push a syringe on one side so that the air is pushed through the tube, into the opposite syringe. Repeat this step to ensure all the oxygen can react
- remove the Bunsen burner and leave the apparatus to cool. You will start to see the copper change in colour
- you started with 100ml of air in one of the syringes, but the volume of air will have decreased during the reaction
- you can calculate the volume of oxygen in the air by subtracting the remaining mass of air from 100ml
- the answer should be around 20 or 20% of the air (by volume)
MY CALCULATION:
100-79=21
What is the equation for copper reacting with oxygen?
Copper + oxygen ➡️ copper oxide
Why should the Bunsen burner be moved along the tube containing the copper?
To ensure that all copper particles are heated so that the test is more fair and accurate
Why should the copper be in excess?
So that there is enough copper for all of the oxygen to react with and ensure that all the oxygen is able to react
Why does the plunger go outwards initially when heating started?
- because as the gas is heated, its volume increases so the plunger is pushed outwards
- any excess water, air etc is evaporated off the copper and will join the air
Why should the apparatus be allowed to cool fully before the final reading on the gas syringe is taken?
The gaps between particles expand when heated, so the results would be falsely high. When the apparatus is cooled, the volume decreases and is more accurate.
What happens in an oxidisation reaction?
Oxidation is the loss of electrons from a substance. It is also the gain of oxygen by a substance. For example, magnesium is oxidised when it reacts with oxygen to form magnesium oxide:
magnesium + oxygen → magnesium oxide
2Mg + O2 → 2MgO
What happens in a reduction reaction?
Reduction is the gain of electrons by a substance. It is also the loss of oxygen from a substance. For example, copper(II) oxide can be reduced to form copper when it reacts with hydrogen:
copper(II) oxide + hydrogen → copper + water
CuO + H2 → Cu + H2O
What is a redox reaction?
A reaction where oxidation and reduction take place at the same time.
What are the oxidising agent and the reducing agent?
- the oxidising agent is the chemical that causes oxidation
- the reducing agent causes the other chemical to be reduced
What substance is formed when metals react with oxygen?
A metal oxide
What is the observation of sulphur burning in air?
Starts to turn red and melts
What is the observation of carbon burning in air?
Red/yellow flame is emitted
What is the observation of magnesium burning in air?
Bright white flame is emitted
What is the observation of sulphur burning in oxygen?
Blue flame is emitted
What is the observation of carbon burning in oxygen?
Bright red/yellow flame is emitted
What is the observation of magnesium burning in oxygen?
Extremely bright white flame is emitted
What is the appearance of the product of burning sulphur?
red liquid
Colourless gas
What is the appearance of the product of burning carbon (e.g metal carbonates)?
Colourless gas (carbon dioxide)
What is the appearance of the product of burning magnesium?
White, powdery ash
What does the colour of universal indicator go after adding water to the product of sulphur and shaking?
Red (acidic)