Science 7.1 Air PDF

~J o = :. (e} — = = «© ¥p) jo b -y Look at the photo below. The Moon is next to the Earth. However, unlike the Earth, there are no living things found on the Moon. Do you know why? d il Y \ & ¥ 'the%Eafth :’; ! k] L > > \ 1 : g 2 ' ! o re 7 i -1 3" 3 | | the Moon Fig. 7...

~J o = :. (e} — = = «© ¥p) jo b -y Look at the photo below. The Moon is next to the Earth. However, unlike the Earth, there are no living things found on the Moon. Do you know why? d il Y \ & ¥ 'the%Eafth :’; ! k] L > > \ 1 : g 2 ' ! o re 7 i -1 3" 3 | | the Moon Fig. 7.1 Y Why are living things found on Earth but not on the Moon? Major components of air The Earth is surrounded by a layer of air while the Moon is not. The layer of air on Earth is called the atmosphere. This layer of air is essential to living things. Without air, living things cannot survive. What is air made up of? Air is a mixture of gases. It is made up of nitrogen, oxygen, carbon dioxide, noble gases, water vapour and small amounts of other gases. Fig. 7.2 shows the percentages of these gases in air. cErpios 8] - 7.1 Discovery of oxygen Do you know who discovered oxygen? What experiments did he/she do that led to the discovery? Explore more on our Web. noble gases (mainly argon) (0.9%) water vapour and %./ ! other gases (0.07%) ex07s1 carbon dioxide (0.03%) Fig. 7.2 atmosphere nitrogen oxygen £ a KR8 carbon dioxide —F1thx noble gas BER water vapour 7KJ5§ Percentages of the gases in air argon &, =3 =, = 7 Living Things and Air Air is a mixture of (21%), f:) Test for the gases in air Oxygen, carbon dioxide and water vapour are common we test for a found in air. How can we test for these gases? When certain gas, we usually study the following properties: « What colour is it? Does it have a smell? Does it burn? - Can it support burning? gases Does it react with other chemicals? Fig. 7.3 let us Now, do Some properties for testing gases experiments several study to properties the oxygen, carbon dioxide and water vapour. Experiment video a v ! ev07s1 Material and apparatus e e S S e 1 5 gas lighter test tube filled with carbon dioxide 5 hydrogencarbonate indicator | test tube rack 2 limewater | wooden splint T 4 cmesne (test tube filled with oxygen - g s emeoo | : me R — — e 8 Procedure Part A: Testing for oxygen 1. Your teacher will give you five test tubes of oxygen (labelled as O1-05). 2. Observe the colour of oxygen. What colour is oxygen? 4 N/ Wear safety gogsles. of =N 3. = Remove the stopper from test tube O1. Fan the oxygen towards your nose and smell it. What is the smell of oxygen? — = (o — = = « 7] ot = oy = fi L _O\.. Caution Fan the gas towards your nose. éf" Do not breathe in the gas directly! 4. Light a wooden splint. Remove the stopper from test tube O2 and quickly put the burning splint into the tube. Tip * Your action should be qui‘t':k. Otherwise, the gas will escape. e Put the burning splint into the test tube, but not near the mouth of the test tube. What happens to the burning splint? 5. Light another wooden splint. Blow it out to get a glowing splint. Remove the stopper from test tube O3 and quickly put the glowing splint into the tube. What happens to the gloWing splint? burning splint #AZEHAIARKE glowing splint BRIBAIARRR it Living Things and Air E= 6. Remove the stopper from test tube O4. Add a few drops of hydrogencarbonate indicator to the tube. Quickly put the stopper back and shake the tube. What happens to the hydrogencarbonate indicator? 7. hydrogencarbonate indicator Remove the stopper from test tube O5. Add a few drops of limewater to the tube. Quickly put the stopper back and shake the tube. limewater What happens to the limewater? Part B: Testing for carbon dioxide 8. Your teacher will give you five test tubes of carbon dioxide (labelled as C1-C5). Repeat Steps 1 to 7 of Part A with carbon dioxide. Record your observations below and compare the results of the tests for oxygen and carbon dioxide. Results Property What colour is it? What is its smell? What happens to the burning splint? (burns more brightly/goes out) What happens to the glowing splint? (relights/goes out) What happensto the hydrogencarbonate indicator? (state any colour change) What happens to the limewater? (state any colour change) I — —_— 4 hydrogencarbonate indicator x4 & B 18 7R T4 limewater KK \l = Activity 7.1 = « —f =7 pom | «Q p Tests for identifying oxygen and carbon dioxide jab) s Q. P= You are given two test tubes of gases. One contains oxygen and one contains carbon dioxide. How do you find out which one contains oxygen and which one contains carbon dioxide? ' ) ‘ Experiment 7.2 Experiment video % v ! ev0Q7s2 Testing for water and water vapour Material and apparatus dry cobalt chloride paper dropper white tile beaker (100 cm3) forceps hot water Procedure 1. Observe the dry cobalt chloride paper in a desiccator. apheser What colour is it? 2. Use a pair of forceps to take out a piece of dry cobalt chloride paper from the desiccator. Add a drop of water to the dry cobalt chloride paper. What happens to the colour of the cobalt chloride paper? It changesfrom —___________to_ . when water is added to it. cobalt chloride paper & {LihmAR desiccator §7 /8% Pt £ chloride paper | 7 Living Things and Air E 3. chloride cobalt the Hold paper. cobalt chloride A paper ety above a beaker of hot water. Wait one to two minutes. S “wr What happens to the colour of the cobalt chloride paper? Explain your observation. Hot water evaporates which changes the "M forceps piece of dry a pair of forceps to take out another Use parn” e * cobalt chloride paper hot water to dry cobalt chloride paper from Caution Handle hot water with care. 4 S— We have learned the tests for oxygen, carbon dioxide and water vapour. However, there are no simple tests for nitrogen and noble gases as these gases are very unreactive. " _ ¢ Test for oxygen: - It relights a glowing splint. - It causes a burning splint to burn more brightly. e Test for carbon dioxide: - It turns hydrogencarbonate indicator from red to yellow. - s It turns limewater from colourless to milky. | Test for water and water vapour: - Both turn dry cobalt chloride paper from blue to pink. ¢ Test for nitrogen and noble gases: - - There are no simple tests. i ° § .N Checkpoint | 7.1 o e-Checkpoint % «! cp07s1 of lts resu the ws sho ow bel e tabl The X. gas n now unk an on s test ple sim Leo performs three his tests. , Simple test Result Glowing splinf Goes out | Limewater | Turns milky | Dry cobalt chloride paper "Blue in colour Gas X is } A. oxygen. B. carbon dioxide. C. water vapour. D. nitrogen. unreactive R3ERH § \I Q Daily applications of the gases in air = = = «w — The gases in air are useful in many ways. The following shows some examples of their daily applications. ey RO R B 3 ) " 1 v QO o =B =o \ P pun «Q i . o LT8R z B A = i T PSRRI g ] T P g ST g VT Ay TIN5 e, 5 W 0 W - ) ok AX o -k i Oxygen is used to breathing d|fflcu|t|es . e . i T e e T e L help patn wit 3 | Carbon dioxide does not support burning | and is denser than air. It is used in fire | T T Er— i extlngwshers to put out flres © In industry, a mixture of a gas fuel and e s Y e | oxygenis used in cutting metals. Such mixture | | Solid carbon dioxide (dry ice) changes -j Wh'Ch IS h'Qh enough for CUtt'nQ metals. " used on stages to produce a fog effect. | directly to a gas at room temperature. It is | burns to produce a very high temperature | ----..--—r-..-‘a-‘---.-~~— R Pt g oy = e LU - 1 r s festi3” % —~ ot - <o Fig. 7.4 rylorivep . s . — ———— - — P AL OB i T AR N A WA A Pt R . B>t . . » . — . . v e r——— o . - : T g N7 B i g A L b ;_-,';:\ you know other daily /Do Some daily applications of the gases in air ——— Neon IS used to il advertlsmg lights. Heliumis sed to fill balloons and airships. Argon is used to fill Ilght bulbs. . TR L|qu1d-n|t'rogen(W|thateeraturebelow -196 °C) is used for storing living cells and tissues. Nitrogenis used to fill some food packages. It helps prevent the food from going bad. oy — 4 ' applications of these gases? . Search the Internet ta.learn mare. - L] L AN fog effect fi%?&fl% helium & neon il E N A FEE RN NN ENEEREE RN ENENSRSENRESRENEET | 9