Air and Oxygen
What is this liquid? Where is it coming from? On a cold morning have you ever noticed that the inside of the car window was covered in moisture? What is this liquid? Where is it coming from?
Investigation to see if there is water vapour in the air! Wait to see what happens
The cobalt chloride paper changes colour from blue to pink – Showing that there is water in the air, that condenses when it hits the cold test tube
Carbon dioxide (CO2) Is a colourless, odourless gas It is special because it sublimes How do we know that it is in air?
To show that there is carbon dioxide in air Suck in here Limewater
Result Eventually the limewater turns cloudy or milky in colour. This shows that there is carbon dioxide in the air
Experiment
To show that oxygen makes up almost 1/5 of air Steel wool Graduated cylinder Water trough Leave for about one week.
Result One week later … The steel wool rusts. Water rises up the cylinder to replace the oxygen used up. Steel wool rusted Water risen up cylinder
Therefore, oxygen is present in air in the proportion of one-fifth. Why does this happen? As the steel wool rusts, it uses up the oxygen in the air. Water rises up the cylinder to replace the oxygen used up, to approximately 1/5th of the height of the cylinder. Therefore, oxygen is present in air in the proportion of one-fifth.
The make up of air
Making oxygen gas (O2) Hydrogen peroxide Oxygen + Water But this reaction takes a long time to happen .. It’s very slow!
A catalyst is something that changes how fast a reaction happens without getting used up itself!
Manganese Dioxide (MnO2) To make this reaction happen faster we can add a catalyst. Catalyst used: Manganese Dioxide (MnO2)
A quick way to make oxygen! Word equation: Manganese Dioxide Hydrogen peroxide Oxygen + Water Chemical equation: Mn02 2H202 O2 + 2H20
A quick way to make oxygen!
Properties of oxygen It is an odourless, colourless gas It has a pH of 7 – it is neutral It aids combustion (helps things to burn!)
A special test for oxygen! It relights a glowing splint
Reactions of oxygen!
When an element is burned in air, a compound called an oxide is formed Carbon + oxygen Carbon Dioxide Magnesium + oxygen Magnesium oxide
A quick way to make oxygen!
Reaction of magnesium with oxygen When magnesium reacts with oxygen we can see… When magnesium oxide is tested with litmus paper red litmus goes ________ blue litmus goes ________ This tells us magnesium oxide is _____________
Reaction of carbon with oxygen When carbon reacts with oxygen, it burns bright ____ When carbon dioxide is tested with litmus paper red litmus goes ________ blue litmus goes ________ This tells us carbondioxide is _____________
Uses of oxygen 1. Oxygen can be stored in cylinders to support breathing.
Uses of oxygen 2. WELDING! Oxygen is used to burn metals at very high temperatures.