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KS3 SCIENCE Quizzes

GCSE KS4 Science-CHEMISTRY

Advanced Level CHEMISTRY

docbgaspreparation updated Jan 17th 2007

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KS3 Science Quizzes

Chemistry

GCSE-IGCSE-KS4

GCE-AS-A2-IB

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Gas preparation and collection methods

  HAZARD WARNING SYMBOLS

(c) doc b

Ex 1. Method for preparing and collecting a gas less dense (lighter) than air by heating solid reactants. The less dense gas rises into, and displaces, the more dense air. This is called upward delivery.

e.g. (c) doc bHeating a mixture of ammonium chloride and calcium hydroxide solids gives ammonia which has a very pungent odour! and turns red litmus blue. See also Ex 7. method.

2NH4Cl(s) + Ca(OH)2(s) ==> CaCl2(s) + 2H2O(l) + 2NH3(g) 

To make dry ammonia you need a U tube packed with granules of calcium oxide between the horizontal pyrex tube and the vertical inverted collection test tube.

(c) doc bOR(c) doc b

Ex 2. Method for preparing and collecting a gas less dense (lighter) than air by reacting a liquid and a solid. The less dense gas rises into, and displaces, the more dense air. This is called upward delivery.

(c) doc b(c) doc be.g. A mixture of zinc and hydrochloric acid makes hydrogen. Hydrogen gives a squeaky pop! with a lit splint. See also methods Ex 5., Ex 6. and Ex 7.

Zn(s) + 2HCl(aq) ==> ZnCl2(aq) + H2(g) 

 (c) doc b

Ex 3. Method for preparing and collecting a gas more dense (heavier) than air by heating the reactants. The more dense gas sinks down into, and displaces, the less dense air. This is called downward delivery.

eg (c) doc b(c) doc bMaking nasty brown nitrogen dioxide by heating lead(II) nitrate crystals (thermal decomposition). The solid 'deflacrates', it crackles as the gas formed splits the crystals apart. See also method Ex 7.

2Pb(NO3)2(s) ==> 2PbO(s) + 4NO2(g) + O2(g) 

Ex 4. Method for preparing and collecting a gas more dense (heavier) than air by reacting a solid and a liquid. The more dense gas sinks down into, and displaces, the less dense air.  This is called downward delivery. Examples:

(c) doc b 

OR collected in boiling tube(c) doc b

(i) Calcium carbonate (limestone/marble chips) with hydrochloric acid makes carbon dioxide. Can also be done via Ex 6. but carbon dioxide is moderately soluble and does make 'carbonated water. See also Ex 8. for carbonate test.

CaCO3(s) + 2HCl(aq) ==> CaCl2(aq) + H2O(l) + CO2(g) 

(c) doc b(c) doc b(ii) Sulphur dioxide from solid sodium metabisulphite or sodium sulphite and excess dilute hydrochloric acid. The nasty choking gas turns potassium dichromate(VI) paper from orange to green. Should be done in fume cupboard.

Na2S2O5(s) + 2HCl(aq) ==> 2NaCl(aq) + H2O(l) + 2SO2(g) 

or Na2SO3(s) + 2HCl(aq) ==> 2NaCl(aq) + H2O(l) + SO2(g) 

(c) doc b(c) doc b(iii) Nasty acrid Hydrogen chloride is formed when conc. sulphuric acid is mixed with solid sodium chloride. Should be done in fume cupboard.

NaCl(s) + H2SO4(l) ==> NaHSO4(s) + HCl(g) 

(iv) (c) doc b(c) doc bChlorine from conc. sodium chlorate(I) and conc. hydrochloric acid.

Very dangerous and should be done in a fume cupboard.

NaClO(aq) + 2HCl(aq) ==> NaCl(aq) + H2O(l) + Cl2(g) 

All of these can be done via Ex. 5 or Ex 7.  below.

(c) doc b Ex 5. Method for preparing and collecting a gas of any density by reacting a solid and a liquid at room temperature. e.g. making carbon dioxide Ex 4., chlorine Ex 4., hydrogen Ex 2., hydrogen chloride Ex 4., oxygen Ex 6., sulfur dioxide Ex 4.
 (c) doc b

This is called collecting over water, or displacement of water or pneumatic trough collection.

Ex 6. Method for preparing and collecting a gas of any density by reacting a solid-liquid, as long as the gas is not too soluble in water! (dissolving or reacting). All gases are less dense than air and will displace the water downwards. No good for soluble gases like ammonia, hydrogen chloride, nitrogen dioxide or sulphur dioxide. You can collect in inverted gas jar if bigger sample required. You have to watch for 'sucking back' effects. Examples:

(c) doc b(i) Making oxygen from hydrogen peroxide solution using manganese dioxide catalyst. Oxygen has similar density to air so must be collected by methods Ex 5., Ex 6. or Ex 7.

2H2O2(aq) ==> 2H2O(l) + O2(g) 

(ii) Hydrogen, (iii) carbon dioxide and (iv) chlorine (moderately soluble, makes 'chlorine water')

(c) doc bEx 7. Method for preparing and collecting a gas of any density by reacting a solid-liquid or heating solids. The angled boiling tube minimises the risk of contaminating the gas syringe with solids or liquids eg making ammonia or nitrogen dioxide. Its a smaller scale alternative to Ex 5. and using a Pyrex tube suitable for small scale heated experiments.
 (c) doc b Ex 8. A simple way to test for a carbonate. Add acid to the suspected carbonate. Collect a sample of the gas in a teat pipette from just above the reaction mixture. Bubble the gas sample into calcium hydroxide solution (limewater) and a milky white confirms the gas is carbon dioxide formed from the original carbonate.

(c) doc bU tube

(c) doc bdreschel bottle

Ex 9. Use of a U tube. This is useful if the dry gas is needed. It is inserted in the apparatus set-up between the reaction container and the gas collection system. It is packed with a solid water absorbing drying agent e.g. anhydrous calcium chloride (not for ammonia), calcium oxide (not acidic gases like sulphur dioxide, carbon dioxide and chlorine), anhydrous sodium sulphate.

A dreschel bottle can also be used e.g. the gas is bubbled through concentrated sulphuric acid which will dry the gas. It cannot be used to dry alkaline gases like ammonia, with which it will react exothermically to form the solid salt ammonium sulphate.

(c) doc b(c) doc bEx 10. A cracking experiment. This diagram outlines a way of demonstrating cracking larger hydrocarbons into smaller molecules. This is a thermal decomposition reaction catalysed by aluminium oxide (or broken porous pot). The gases produced can be tested with (i) a match! and (ii) bromine water, if it is decolorized from orange to colourless, then unsaturated alkenes were formed. This is another example of over water, or displacement of water collection. The dreschel bottle is to collect any sucked back water if the hot gasses cool and contract. Cold water on the hot Pyrex tube has very nasty effect! plus the risk of fire!
   
   

KS3 SCIENCE * KS4 SCIENCE GCSE IGCSE GCE AS A2 IB CHEMISTRY * SITE PURPOSE EDUCATION - online learning or 'self-private-tuition' using revision notes, quizzes, practice tests involving SCIENCE in the areas of REVISING only the CHEMISTRY-Earth Science-Radioactivity at Doc Brown's Chemistry Clinic via HOMEPAGE in secondary school/schools, 6th form college/colleges, academy/academies or home self-study and may help with 1st year undergraduate university chemistry courses. Hopefully it will encourage interest and understanding of Chemistry, Earth Science and Radioactivity in any country of the world, though the site is written entirely in English. The website is designed to help and unofficially support students/teachers revise-learn/teach the chemistry for modular or co-ordinated examination science courses from UK QCA based AQA, OCR (Oxford and Cambridge) Twenty First (21st) Century and Gateway Science, Edexcel 360Science , Nuffield, Salters, Cambridge International (CIE), London International, WJEC, CCEA exams etc. Also, national award assessments-examinations for GCSE-IGCSE-KS4-O level-BTEC-NVQ applied, additional and chemistry science courses and examinations, Advanced Subsidiary Level GCE-AS-A2-IB-KS5-BTEC-NVQ National Chemistry assessment levels, KS3 SATs Science-biology/chemistry/physics (SAT revision levels 3-5 or 5-7) and covers much of the revising, learning and teaching chemistry of the International Baccalaureate, K12 US grade 6,7,8,9,10,11,12,AP basic level examinations courses for the national curriculum for secondary schools and colleges. The site does not support the content of England, Wales or Northern Ireland primary science KS1 or KS2. The notes should also provide some background theory for a coursework assignment or a project. BUT please note that my on-line revision notes and quizzes are no substitute for good classroom teaching-lecturing and thorough studying of your own notes and textbooks, practicing past papers and a copy of the syllabus which are readily downloaded from the examination board sites, but I hope here and there they will lend a tutoring hand on some topic, unit, module etc. For final revision you have to be intellectually honest about what you don't know or follow, YOU have to take the stuff to pieces, analyse what you do/do not understand and reconstruct it so it all makes sense in the end. There is no other way, there are no magic secrets on how to revise and learn, its mainly down to hard work and just good old fashioned study and employing teach-yourself strategies without the need for extra tutors and tutoring lessons. I also think there is too much hit and miss revision using past papers (which I do NOT supply) and not enough systematic revision. I also hope it will help teachers in planning lessons and developing schemes of work for science-chemistry. There are no lesson plans on the site but there are plenty of quizzes to incorporate into classroom activities whether photocopied or on electronic whiteboard projector for use as self-tuition-assessment purposes and a variety of teaching and learning styles and the images may be used in Microsoft Word documents and powerpoint projections. The site seems to be used by a large number of home study tutors, particularly the revision notes. An individual tutor may printout out the notes for science-chemistry learning teaching-tuition purposes and for background material for assignments and projects. I have no interest or time in producing WORD.doc or xxxx.pdf revision notes files of the notes at the moment. Neither have I time to write up many practical laboratory experiments ('lab'-'labs') at the moment, but the notes contain lots of background information of chemical reactions in terms of observations-balanced equations-reactants-products-theory etc. I also find it difficult to recommend specific exam websites or syllabus textbooks, it depends exactly on what you need, what you have time for, and there are so many of them to choose from and I do not supply past examination papers for classes. The sites resources include revision notes, quizzes and worksheets which provide support for home study or tuition for homework and coursework help e.g. science investigations for any of the key stage courses indicated, but I do not supply lesson plans. Dr W P Brown I 29-11-2007 * KS3 SCIENCE * KS4 SCIENCE GCSE IGCSE GCE AS A2 IB CHEMISTRY

useful alphabetical site index

Online free help resources for Key Stages 3 SATs (S.A.T.s), 4 & 5AQA, Edexcel, OCR, CIE GCSE IGCSE BTEC Science, GCE, AS, A2 Advanced subsidiary Chemistry A levels, IB Diploma and US K12 (K-12 grades) courses and examinations and revising for the various syllabuses and specifications. Exploring the site for lessons, plans, ideas for projects and coursework, professional development. Through hard work the site has been built up over the course of many years with no need of special pc software except FrontPage and Hot Potatoes (uvic) for quizzes and worksheets. It is used in the classroom, home learning-tutoring-schooling and guidance, private tuition, school retakes revision. Whether you are a teacher/tutor teaching, a student studying, using the pages as self-study guides for your science-chemistry studies etc. etc. I hope the site supports your endeavour. 15-12-07 © Dr W P Brown

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KS3 SCIENCE Quizzes

GCSE KS4 Science-CHEMISTRY

Advanced Level CHEMISTRY

docbgaspreparation updated Jan 17th 2007

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