5. INORGANIC Qualitative TESTS Anions and Alkalis

Acid is added to the solid carbonate in a test tube. You could also collect a sample of gas from a heated carbonate, i.e. the solid is where the liquid is in the left hand test tube.

Methods of gas preparation are described in more detail on another page.

(ii) Effect of fairly strong heating and testing for any carbon dioxide given off.

Test (ii) will distinguish sodium hydrogencarbonate (NaHCO₃ readily decomposes - 'baking powder') from anhydrous sodium carbonate (Na₂CO₃, thermally very stable).

(ii) There might be colour changes in the solid, but you need to collect a sample of gas from just above the heated solid to see it gives a white precipitate with limewater.

Apart from hydrated sodium carbonate, sodium hydrogencarbonate is one of the few common carbonates to give off water on heating and condenses on side of test tube, but basic carbonates will also give off H₂O as well as CO₂.

CO₃^2-_(s) + 2H⁺_(aq) ==> H₂O_(l) + CO_2(g)

and for hydrogencarbonate ...

2HCO₃^-_(s) + 2H⁺_(aq) ==> H₂O_(l) + CO_2(g)

(ii) The thermal decomposition equations are for carbonates

MCO_3(s) ==>MO(s) + CO_2(g)

e.g. M = Mg, Zn, CuO and note some give clear colour changes in the solid which might be useful to identify the metal (see heating carbonates in metal cation section)

and for sodium hydrogencarbonate ...

2NaHCO_3(s) ==> Na₂CO_3(s) + H₂O_(l) + CO_2(g)

(ii) Add lead(II) nitrate solution.

(ii) A white precipitate of lead(II) sulphate.

Test (i) is more definitive.

Any soluble barium salt + any soluble sulphate forms a white dense barium sulphate precipitate.

(ii) Pb²⁺_(aq) + SO₄^2-_(aq) ==> PbSO_4(s)

Neither white precipitate is soluble in excess hydrochloric acid.

Test (iii) is easily unreliable, the sulphite ion is oxidised by air (dissolved oxygen) to give the sulphate ion, so you will lucky to obtain a clear solution after adding excess acid.

(ii) Test any gas evolved with fresh potassium dichromate(VI) paper.

(iii) Add barium chloride or barium nitrate solution.

(i) Acrid choking sulphur dioxide gas formed.

(ii) The dichromate paper turns from orange to green.

(iii) A white ppt. of barium sulphite which dissolves in excess hydrochloric acid to give a clear colourless solution.

(ii) The sulphur dioxide reduces the dichromate(VI) to chromium(III). Note: sulphites do  not give ppt. with acidified barium chloride/nitrate because sulphites dissolve in acids.

(iii) Ba²⁺_(aq) + SO₃^2-_(aq) ==> BaSO_3(s)

BaSO_3(s) + 2HCl_(aq) ==> BaCl_2(aq) + H₂O_(l) + SO_2(aq)

In test (ii) dangerous hydrogen sulphide is formed.

(ii) If solid, add dil. HCl(aq) acid, test smelly gas with damp lead(II) ethanoate paper (old name lead acetate).

(ii) Rotten egg smell of hydrogen sulphide and the H₂S gas turns lead(II) ethanoate paper black.

(ii) MS_(s) + 2H⁺_(aq) => M²⁺_(aq) + H₂S_(g) (e.g. M = Pb, Fe, Cu, Ni etc.) Then reaction (i) above occurs on the lead(II) ethanoate paper (old name lead acetate).

Cl^-

(ii) If insoluble salt, add conc. sulphuric acid, warm if necessary then test gas as for HCl.

(iii) Add lead(II) nitrate solution. Not a very specific test - test (i) is best.

(ii) You get nasty fumes of hydrogen chloride which turn blue litmus red and give a white precipitate with silver nitrate solution.

(iii) A white ppt. of lead(II) chloride is formed.

Any soluble silver salt + any soluble chloride  gives a white silver chloride precipitate, that darkens in light.

(ii) Cl^-_(s) + H₂SO_4(l) ==> HSO₄^-_(s) + HCl_(g) ,

then Ag⁺_(aq) + Cl^-_(aq) ==> AgCl_(s)

(iii) Pb²⁺_(aq) + 2Cl^-_(aq) ==> PbCl_2(s)

Br^-

(ii) If insoluble salt, add conc. sulphuric acid, warm if necessary.

(iii) Add lead(II) nitrate solution. Not a very specific test - test (i) is best.

(ii) Orange vapour of bromine and pungent fumes of SO₂, test for sulphur dioxide.

(iii) A white ppt. of lead(II) bromide is formed.

Any soluble silver salt + any soluble bromide gives a cream silver bromide precipitate.

(ii) The bromide ion is oxidised to bromine and the sulphuric acid is reduced to sulphur dioxide.

iii) Pb²⁺_(aq) + 2Br^-_(aq) ==> PbBr_2(s)

Iodide ion

I^- 

(ii) If insoluble salt can heat with conc. sulphuric acid, (ii) get purple fumes of iodine and very smelly hydrogen sulphide, (iii) if soluble, add lead(II) nitrate solution.

(iii) If iodide soluble, add lead(II) nitrate solution.

(ii) purple vapour and rotten egg smell!, (iii) a yellow precipitate forms

(i) Yellow precipitate of lead(II) iodide. Not too definitive -Test (i) best.

(ii) iodide ion is oxidised to iodine and the sulphuric acid is reduced to 'rotten eggs' smelly hydrogen sulphide,

(iii) insoluble lead(II) iodide formed

Pb²⁺_(aq) + 2I^-_(aq) ==> PbI_2(s)

(ii) Add iron(ii) sulphate solution and then conc. sulphuric acid (the 'brown ring' test)

(iii) Strongly heating nitrates of M²⁺ salts.

(i) the fumes contain ammonia, which turns red litmus blue, see ammonia test details

(ii) Where the liquids meet a brown ring forms

(iii) Nasty brown gas (beware!) of nitrogen (IV) oxide (nitrogen dioxide)

(ii) NO complex of iron(II) formed

(iii) a general thermal decomposition equation for this reaction is

2M(NO₃)_2(s) ==> 2MO_(s) + 4NO_2(g) + O_2(g)

where M = Pb, Zn, Mg, Cu etc.

NH₄⁺

 NH₄⁺_(aq) + OH^-_(aq) ==> NH_3(g) + H₂O_(l)

(ii) Add a little sodium hydrogencarbonate powder.

(ii) Fizzing with any carbonate - test for CO₂ as above.

(ii) HCO₃^-_(aq) + H⁺_(aq) ==> H₂O_(l) + CO_2(g)

(ii) Add a little of an ammonium salt.

(ii) If strongly alkaline ammonia should be released, see ammonia test for rest of details

(ii) Ammonia released from the salt.

NH₄⁺_(aq) + OH^-_(aq) ==> NH_3(g) + H₂O_(l)

Chromate(VI) ion

CrO₄^2- (yellow)

These tests are not very definitive, but collectively they are a good 'pointer'!

(ii) Add barium chloride/nitrate solution.

(iii) Add lead(II) nitrate solution.

(ii) A yellow precipitate of barium chromate(VI) is formed.

(iii) A yellow precipitate of lead(II) chromate(VI) is formed. 'lead chromate'

(ii) Ba²⁺_(aq) + CrO₄^2-_(aq) ==> BaCrO_4(s)

(iii) Pb²⁺_(aq) + CrO₄^2-_(aq) ==> PbCrO_4(s)

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

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. scientific investigations, educational development, scientific exhibitions, scientific adventures, science projects, fantasy science, science fiction, interesting science demonstrations, fascinating science experiments, science education conferences, scientific expeditions, scientific information and databases, revision tutoring resources for syllabuses specifications examinations, chemical physical biological forensic science, scientific applications, science-chemistry tuition courses