Charlene Sci 7.1 Practicals PDF

V Flipped classroom Letsibegin The photo below shows part of the Earth viewed from space. The Watch a video and answer Earth is surrounded by a layer of air cal...

V Flipped classroom Letsibegin The photo below shows part of the Earth viewed from space. The Watch a video and answer Earth is surrounded by a layer of air called the atmosphere”. This the questions. layer of air is very important to the survival of living things on Earth. What is air made up of? A What is air made up of? Ao Link Air is a mixture” of gases. It mainly contains nitrogen’ (78%) and You will learn more oxygen’ (21%). It also contains small amounts of carbon dioxide” about mixture in Bk 38, (0.04%), noble gases” (e.g. argon’, neon” and helium”), water vapour Unit 13. and other gases (Fig 7.1). A mixture is formed when two or more substances mix with each other without the formation of a new substance. The substances in a mixture are not chemically joined together. Key: Qo nitrogen molecule Qo oxygen molecule @ neon (a noble gas) atom @ag carbon dioxide molecule a® water molecule PEED PPPPPEPPRPppprrpyrpppmpeyreppprrerr rer PTT YT TT TT TTT ITT IT RIL ERT STAAL RAL Ld dd LE EE EL LE ET EE EL Ey Ey Ey LY TTT POOP PUPP TTT TL 2 atmosphere A§ mixture ;B2% nittogen &® oxygen & carbon dioxide Z&{LHX noble gas EF 52 argon neon helium &  Fig 7.2 shows the percentages of the gases in air. carbon dioxide (0.04%) noble gases (about 0.9%) water vapour and other gases (variable) Fig 7.2 Composition of air 5 v be I"' Sor * Wh RY y BY 14 a ARS X : 2 V& In 5 aTh F Fe a & ¥ A we id reSE l nobl e gas ig re = Sa 4 (33 Tests for gases in air It is difficult to identify” a gas by just looking at it. Scientists developed tests to identify gases based on their properties. Let us carry out Practical 7.1 (p. 4) to study the properties of oxygen, carbon dioxide and nitrogen, and see what tests can be used to identify them. DTT LLL r TTL L Tr TL LL LE LLL LLL ETE EE EE REAR ALAR REEL E identify #32  Pr actical 7.2 \ Test for water (water vapour) Aim To test for water with dry cobalt chloride paper Co ——— —— —— | Apparatus and materials per group | dropper 2 dry cobalt chloride paper” forceps 1 pair distilled water white tile 2 alcohol™ (100%) | beaker (glass or plastic) (250 cm?) 2 BR 1 Take out a piece of dry cobalt chloride paper from the desiccator” using a pair of forceps. Put it on a white tile. Record the colour of the paper. «4 Before the practical, the dry cobalt chloride dry cobalt a paper is kept in a chloride paper desiccator to prevent it from absorbing the ” moisture in the air. Do not touch the A ? —desiccator dry cobalt chloride paper with bare hands. Otherwise, | | the moisture on your By ————— drying agent hands will change the x 4 colour of the paper. 2 Use a dropper to add a drop of water to the dry cobalt chloride paper. Record the colour of the paper. 3 Use another dropper to add a dropof alcohol to a new piece of dry cobalt chloride paper. Record the colour of the paper. Caution * Wear disposable gloves. e Alcohol (100%) is flammable and harmful. Avoid contact with skin. «-«-s=s=e--+ Ensure the room is well-ventilated. Use it only in the absence of naked flame. EE LL LE EE. I LLL EL LE EE cobalt chloride paper &{c#tst4k alcohol jB¥ desiccator Figs  Results Colour of Colour of cobalt chloride paper after adding... dry cobalt chloride paper Discussion What do the results show? Dry cobalt chloride paper changes from blueto Pl in the presence of water. P nk to Blue Key point Test for oxygen: e [trelights a glowing splint. Tests for carbon dioxide: { e It turns hydrogencarbonate indicator from red to yellow. e It turns lime water from colourless to milky. ~ Test for water: eo It turns dry cobalt chloride paper from blue to pink. pm“ Did you know? (+ } | | & | Discovery of oxygen ‘Animation Before the 18th century, the existence of oxygen in SY air was not known. In 1775, Antoine Lavoisier® did an investigation on burning. During the investigation, he discovered oxygen. Watch the animation about this discovery and think about the questions below. 1 How did the understanding of burning change over time? 2 Was there any competition or collaboration™ between scientists in the discovery of oxygen? Fig 7.3 Antoine 3 How did the advancement in technology lead to the Lavoisier change in the understanding of burning? PP PPP TL LLL Tr TT TT TT TY ron pppapeppemppappappppaepeeerrr PT TT TT TY PT PT TT TTT TR TLR ALLEL 0 2 2 dd a A LA SA LE I LL EE TL EE ad Ld EL dd dd dd id dd dd ddd dl dd dE id tid iid ad Ada a ad dL EE dE Ed LE Ed EE dn Led a Ed Antoine Lavoisier f1FL$5 collaboration &{E OQ  C: Properties and uses of gases in air Oxygen, carbon dioxide and nitrogen are all colourless and odourless* gases, but they have special properties of their own. These properties make the gases useful in certain areas. Below are some examples. Oxygen LEE = — L codes heut -0¥f#°" 1 Oxygen supports burning. ~¢,/ A! In a welding torch”, Oxygen is used oxygen is mixed to support the with a fuel gas. burning of fuel Burning the mixture for propelling” gives a very hot rockets. flame for cutting and welding” metals. 2 Oxygen is essential for the survival of humans. Air with higher Bottled oxygen is oxygen content is used when people given to patients are climbing at with breathing high altitudes, difficulties. where obtaining oxygen bottle oxygen from the air is more difficult. 3 Enid A fo Tn Se > a Tm Some fire extinguishers” contain carbon dioxide. Carbon dioxide released from the fire extinguisher sinks and displaces the air surrounding the fire. This cuts off the oxygen supply and helps put out the fire. ERR RAR RR EE EEE TE ) AAA « RE EE EEEEY ALAA LAA Ad Ad Ed AL ELL TI ELL litt add LIE LL IE IE YT TT TET YY YY YY YY YY TY PrP pen LA EE ENR I TT raed intaae AXE. RERE RE ve Bee eee testes ” ¢ ! ‘ odourless FAKE) welding torch (#18  After-class activity (5 } Search for more uses of oxygen, carbon dioxide and nitrogen in our daily lives on the Internet. 5 Some substances in food react with oxygen in air, causing the he food to turn bad. Nitrogen is used to replace the air in food i packets. This helps prevent the food from reacting with oxygen, a so the food can be kept longer. £2 Nitrogen has a very low boiling point (-196 °C). Liquid nitrogen is very cold. hi Liquid nitrogen Liquid nitrogen is i can be used in the used in commercial : storage of living freezing systems : cells or tissues to freeze foods like : (e.g. cord blood”). fruits rapidly. tank with “Yc. Jiquid nitrogen CE Th RESET 2 Trot 0 peor TERME ROR Tre 3B TE Hr Euan REG ii oy 2 ig : Se ; : ges to gasdirectly athe75 °C (i.e. without going : Ean, 4 omenis used tovit sii Bivicice is commonly aL aused on the stage ERS to AT is ‘produce the effect of | SE ERT | | dense fog gins oe 5 SSR bobs adenine anim nc th inti ution if tn alias is odio dud liu iitin on dnic db dunn idiots bin ba uid dab Quit i lh il dk id iii TT PI ET ry 1.0 TL LL rt Tree ge Wy Or PPV Ves FR 0 FA RT YA aed ol Aid Aided cord blood #510 11  Noble gases Noble gases are very unreactive. They are also useful in many ways. For example: Helium is used to fill balloons. As helium is less dense than air, helium-filled balloons float in air. Argon and neon are used to fill neon signs™. The ~ tubes filled with these gases give off coloured light when ~ electricity passes through them. wo SocHON SUT DY YP DE SSR SE 1 Airis a mixture of gases. It contains nitrogen (78%), oxygen (21%), carbon dioxide (0.04%), noble gases (about 0.9%), water vapour and other gases. 2 Tests for oxygen, carbon dioxide and nitrogen, the properties of these gases and some of their uses: i Bie's pi Properties Examples of uses 5 3 : | Oxygen e Relights a glowing e Supports burning Mixed with a fuel gas to splint produce a flame for cutting and welding metals e Used to help patients with breathing difficulties ee - - — — av — Carbon | ¢ Turns * Does not support e Used in some fire dioxide hydrogencarbonate burning extinguishers | indicator fromredto | e Denser than air | « Used on the stage to produce | yellow | * Changes from the effect of dense fog | ® Turns lime water from | solid to gas e Used to keep frozen food colourless to milky directly at —78 °C cold igs CL i i ip) | To e No simple test |r Unreactive 1 e Used in food packaging | | | * Very low boiling e Used in the storage of living | point (~196 °C) cells or tissues | Used to freeze food rapidly asa A Em mm — rr ————— BR. - — 3 Water turns dry cobalt chloride paper from blue to pink. LT TT Ta PPP PPP PIT TTT 1 LT TT Tr Trrvonssprprrrrproppeeprr pr YY TTY TT FITZ TIALS IRI RL LASALLE SA 402 Add dd ddd d dit iibidisdiitdtididdddbiddiid did id ddd dd ddd dad idl idl ddl dIl ILI tT ITTY TY IY YY PTY rr rrrorer rr PY PPE TERI RT RR T RZ 12 neon sign EAI/& Lo BECHON EXEECISe LT RL [Level1 1 Which of the following shows the gases in 2 A burning splint is put into a test tube of an ascending order of their percentages in air? unknown gas. It burns more brightly. What A Nitrogen, oxygen, carbon dioxide is the gas? B Carbon dioxide, oxygen, nitrogen A Carbon dioxide C Oxygen, nitrogen, carbon dioxide B Water vapour D Carbon dioxide, nitrogen, oxygen C Nitrogen Ww D Oxygen ¢p.3 LL €p.7 Level 2 3 A student took a cup of ice cream out of a refrigerator. After a few minutes, he saw drops of colourless liquid formed on the outer surface of the cup. R ~~ - far CARLY we - w a The student tested the liquid using a piece of dry cobalt chloride paper and the paper turned pink. What does this indicate? (1 mark) drop of colourless liquid © €p.9 b The dry cobalt chloride paper is usually stored in a desiccator. Why? (1 mark) &p.3 ¢ Dry ice is used to keep the ice cream cool during transport. Suggest an advantage of using dry ice over using ice (i.e. water in solid state). (1 mark) &p. 11 d The student collected the gas released from dry ice using a test tube. He then added lime water to the tube and shook the tube. State the expected colour change of the lime water. (1 mark) &p.9 13