2.3 - Gases in the atmosphere Flashcards
What is combustion of air?
-The proportion of gases in the air has not changed much in 200 million years about four fifths of the air is nitrogen and one fifth is oxygen the remaining gases include carbon dioxide, water vapour and traces of quantities of the noble gases
What is the percentage of different gases in the air
78% nitrogen, 21% oxygen, 0.9% argon, 0.04% CO2
What are the different methods of determining the percentage of oxygen in the air
-There are a few different methods for measuring the percentage of oxygen in the air. All methods rely on the same basic principle reacting something with oxygen in the air and look at how much the volume decreases as the oxygen is removed.
What is combustion and what is the equation?
Combustion is the process of burning a substance with the release of heat and light in the presence of oxygen is called combustion.
Fuel + oxygen = carbon dioxide +water + energy
What is the method for the Copper syringe experiment?
-The plunger on one of the gas syringes is pushed all the way in, and the other one moved out to 100cm3. The apparatus now contains 100cm3 of air
-The silica tube is heated strongly with a roaring Bunsen flame
-The plunger in the left hand gas syringe is pushed this causes the air to pass over the heated copper this pushes out the plunger on the right hand gas syringe. The plungers are pushed in sequence so that the air in the system keeps passing over the heated copper. The pink-brown copper turns black as copper(II) oxide is formed. As the copper reacts the Bunsen burner is moved along the tube so that it is always heating fresh copper
-The volume of gas in the syringe falls as the oxygen is being consumed
-The plungers should keep being pushed in and out until there is no change in volume. The apparatus is then allowed to cool to room tempreture again before taking the final volume of gas because gases expand as they are heated
What are the results of the copper syringe experiment ?
Initial volume of air in the system/ CM3- 100
Final volume of air in the system/ CM3- 79
-The volume of the air has been decreased because the oxygen has been removed as it reacts with the copper. The reaction that occurs is:
What is the chemical equitation for the copper syringe experiment?
2Cu(s) + O2 (g) > 2CuO (s)
What is the phosphorous in a bell jar experiment?
-The apparatus in the diagram is set up with the piece of phosphorus on an evaporating basin which is floating on the water.
-The initial level of water is marked on the side of the bell jar with a waterproof pen or a sticker. The bung is removed from the bell jar and the phosphorus is touched with a hot metal wire in order to ignite it. The bung is quickly put back into the bell jar.
-The phosphorus burns, the bell jar becomes filled with a white smoke, Phosphorus oxide , and the level of water rises inside the bell jar. The smoke eventually clears as the phosphorus oxide dissolves in the water.
-When the water levels stop rising in the bell jar the final level is marked. To find out how much the water level has changed the bell jar is turned upside down filled with water to each mark in turn and the water is poured into a large measuring cylinder. It is important that there is still some phosphorus left on the evaporating basin at the end of the experiment. There has been an excess of phosphorus so that there is more than enough to react with all of the oxygen if there was no phosphorus left then there would be a lower value and lower level of oxygen in the air because not all of the oxygen might have been used up.
What is combustion of elements in oxygen?
-Some elements burn in oxygen, these reactions are called combustion reactions. Elements burn more brightly and rapidly in pure oxygen than in air because air only contains 21% oxygen
How does magnesium combust in O2
-Magnesium burns in oxygen with extremely bright white flame to give a white powdery ash of magnesium oxide.
2Mg(s) + O2(g) > 2MgO(s)
The white powder formed is not very soluble in water but does have a very small amount does dissolve to form an alkaline solution
MgO (s) + H2O(l) > Mg(OH)2(aq)
How does sulfar combust in O2
-Sulfar burns in oxygen with a blue flame. Poisonous, colourless sulfur dioixde gas is produced
S(s) + o2(G) > SO2(G)
The sulfur dioxide dissolves in water to form an acidic solution of sulfurous acid
SO2(G) + H2O(L) > H2SO3
How does hydrogen combust in H2?
-Hydrogen burns in oxygen with z pale blue flame the product is water
2H2(g) + 2(G) > 2H20
If you ignite a mixture of hydrogen and oxygen it will explode. This is the basis of the ‘squeaky pop’ TEST FOR HYDROGEN
What are the properties of metal oxides
-Metal oxides are ionic compounds containing O2- ions, Metal oxides are usually basic oxides, which means that they react with acids to form salts. Metal oxides are usually insoluble in water react with it to form alkaline solutions containing hydroxide (OH-) Ions.
What are the properties of non metal oxides
-Non metal oxides are covalent compounds. Non metal oxides are usually acidic oxides, which reacts with alkalis to form salts. Non metal oxides are often soluble in water and react with it to form acidic solutions containing hydrogen (H+) ions.
What is carbon dioixde?
-Carbon dioxide is a colourless gas that is more easily made in the laboratory by the reaction between dilute hydrochloric acid and calcium carbonate in the form of marble chips.
-Carbon dioxide can also be obtained when metal carbonates are heated strongly. Most carbonates split to give the metal oxides and carbon dioxide when they are heated. This is an example of thermal decomposition, breaking up something by heating it
-Copper (ii) carbonate is a green powder which decomposes on heating to produce black copper (II) oxide
