the atmosphere the atmosphere is a layer of gases around the earth. these gases are collectively...
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Percentages of gases in the air
• NITROGEN 78%• OXYGEN 21%• CARBON DIOXIDE 0.03%• WATER VARIES• Neon and argon 1%
To show that there is water vapour in the air
1. Set up as shown2. Leave for 30 mins3. Drops of water form on the outside of the tube4. Test water with blue cobalt chloride paper
Result ; the blue cobalt chloride paper turns pink proving that water is present in the air and that the water condensed on the cold test tube.
Another test for water:Water turns Anhydrous copper sulfate(white) to hydrated copper sulfate (blue)
To show that there is carbon dioxide in the air
1. Set up the apparatus as shown in the the diagram2. Use a vacuum pump to draw a current of air
through the lime water in the test tube
Result : after a few minutes the limewater turns milky
Conclusion : the air contains carbon dioxide
1. To show one fifth of air is oxygen1. Pack steel wool in bottom of a graduated cylinder2. Invert cylinder in basin of water3. Mark level of water on the cylinder4. Leave for one week5. Measure height that the water rises up the
cylinder
Result: • When iron rusts it uses up oxygen. When
there is sufficient iron and water present, rusting will continue until all of the oxygen is used up.
Method1.Fill a trough ¼ full with water2.Light a night light and float on water3.Unscrew cap of plastic bottle and place over night light4.Mark the level of the water5.Replace the cap on the bottle tightly6.Observers what happens7.Mark the new level of water in the plastic bottle
ResultThe water rises inside the bottle because the oxygen in the air is used up in combustionCombustion is a chemical reaction in which a fuel reactive with oxygen to give out heat
3. To show one fifth of air is oxygen
• Set up apparatus• Before heating, ensure one syringe contains 100cm3
of air and other is closed• Heat copper turnings and slowly pass the 100cm3
from one syringe to the other• Continue until the volume does not change• Cool down apparatus and record volume.
• Result: • Volume will go down to approx 80cm3 and the
copper turnings turn a grey/black in colour. This is because the copper reacts with the oxygen present forming copper oxide. The oxygen is used up in this process to make the oxide and therefore the volume of oxygen in the air goes down.
Preparation of oxygen
• Oxygen is prepared by the chemical breakdown of hydrogen peroxide H2O2 using manganese dioxide MnO2 as a catalyst
• A catalyst is a substance that speeds up a chemical reactions but are not used up in the reaction.
Equation To prepare and examine oxygen gas
hydrogen peroxide oxygen + water
manganese dioxide
2H2O2 O2 + 2H20MnO2
To prepare and collect oxygen gas
1. Set up as shown2. Open the tap on the funnel and add the
hydrogen peroxide slowly to the black solid manganese dioxide
3. The oxygen gas is collected over water as oxygen is only slightly soluble in water
4. Three test tubes of the gas are collected for tests.
• 4. Heat carbon (charcoal) in combustion spoon over a bunsen and transfer to jar of oxygen, test products with litmus and limewater.
To burn carbon and magnesium in oxygen and test the products using moist litmus paper
• When an element is burned in air, a compound called an oxide is formed.
• Magnesium + Oxygen Magnesium oxide• Carbon + Oxygen Carbon dioxide• Care: Magnesium ribbon burns with an intense
white light that can be damaging to the retina.
Procedure: magnesium• Get a piece of magnesium ribbon• Using a tongs, hold the magnesium in the flame
of the Bunsen burner until it catches fire.• Put the burning magnesium in the test tube of
oxygen. Observe what happens.• Result: A white powder magnesium oxide is
formed. When water is added the magnesium oxide forms a base called magnesium hydroxide. Magnesium hydroxide is a base and it is used to neutralise stomach acid and it is found in Milk of Magnesia.
Properties of oxygen
• Physical properties1. Colourless2. Odourless3. Tasteless4. Slightly heavier than air5. Slightly soluble in water
Chemical properties6. Supports combustion7. Neutral substance – neither acid or base, no effect on litmus
Uses of oxygen
• Burning • Welding• Breathing• Metals and non metals burn in oxygen to
produce oxides
Preparation of Carbon Dioxide
Hydrochloric acid + Calcium carbonate
= calcium chloride + carbon dioxide + water
• Set up as shown• Slowly add the HCl from the tap funnel• Observe the bubbles of CO2 gas produced when
the HCl hits the calcium carbonate.• The Carbon dioxide produced collects in the gas
jar.• Uses of carbon dioxide:1. In fizzy drinks2. In fire extinguishers
Main Uses of Carbon Dioxide CO2
• Fizzy Drinks– All fizzy drinks contain CO2 under pressure
• Fire Extinguishers– CO2 is denser than air and does not support combustion
• Refrigeration– CO2 under pressure can be converted into a solid: Dry Ice. It is much
colder than ice –78oC
• Dry Ice- Special Effects on Stage– Lumps of dry Ice are put into warm water and wet CO2 carries clouds
of water vapour with it. Mist Effect
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