Experiment 6 - Elemental Analysis

ELEMENTAL

ELEMENTAL

ANALYSIS

INTRODUCTION

INTRODUCTION

Elemental Analysis

Elemental Analysis

--used for identication of unno!nused for identication of unno!n com"ounds

com"ounds

--c#ief as"ect ic#ief as"ect in e$"erimental or%anicn e$"erimental or%anic c#emistry

Sodium fusion

-also no!n as Lassai%ne&s test -useful met#od for 'ualitati(ely

determinin% t#e "resence of sulfur) nitro%en or #alo%ens in or%anic

com"ounds

-"ro"erty of sodium to *e a (ery stron% reducin% a%ent maes it "ossi*le to *rea t#e or%anic com"ound&s car*on c#ain into inor%anic ions

Sodium fusion

-t#e ltrate from t#e fused solution of t#e unno!n com"ound and sodium metal is used to conduct t#e

conrmatory tests for t#e "resence of sulfur) nitro%en or #alo%ens

E+,ERIMENTAL

 T#e set-u" for sodium fusion !as done as s#o!n in t#e %ure.

,ea-si/ed sodium !as "laced in a small test tu*e0 T#e test tu*e !as #eated until sodium (a"or !as

o*ser(ed to condense on t#e !all of t#e test tu*e0

 T#e 1ame !as remo(ed and a*out 203% of "-c#loroaniline !as added0

 T#e test tu*e !as #eated %ently to initiate t#e reaction !it# sodium0 T#e 1ame !as remo(ed !#en t#e reaction su*sided t#en it !as #eated to

 T#e red-#ot tu*e !as dro""ed in a 42-mL *eaer containin% 52-42-mL of

distilled !ater

Solution !as ltered and t#e ltrate !as used as t#e test solution

6T#e "rocedure !as re"eated usin% sulfanilic acid7

8ualitati(e Analysis

Sulfur test

9i(e dro"s of fusion solution and 3

dro"s of !ater !ere "laced in a 4-mL test tu*e

: dro"s of :; a'ueous sodium nitro"russide solution !as added

 T#e formation of a dee" *lue-(iolet color !as o*ser(ed

Nitro%en test

A "inc# of 9eSO_< !as added to 5-mL of t#e fusion solution

4 dro"s of 52; solution of =9 !as added

Mi$ture !as *oiled for 4 minutes and : dro"s of 4; solution of ferric c#loride !as added

>M ?_:SO_< !as added to dissol(e t#e iron #ydro$ides and to acidify t#e solution

9ormation of a dee"-*lue "reci"itate indicated t#e "resence of nitro%en

?alo%en test

?alo%en test

 Ten dro"s of t#e fusion solution !as "laced in a test tu*e

If t#e sam"le !as "ositi(e for nitro%en or sulfur) acidify !it# :M ?NO₃

@ently *oil to eliminate ?CN or ?_:S t#at mi%#t *e "resent and cool to room tem"erature

205M A%NO₃ !as added to t#e solution n #ydro$ides and to acidify t#e

solution

A #ea(y and coa%ulated "reci"itate indicated t#e "resence of #alo%ens

?alo%en test

Dierentiatin% C#lorine) Bromine and Iodine

 T#e o*ser(ed colors indicate t#e follo!in%

"reci"itates. A%Cl 6!#ite7) A%Br 6"ale yello!7) and A%I 6yello!7

Dierentiatin% Bromine and Iodine

Add 204-mL of dilute :M N?<O? to t#e "reci"itate

Determinin% if is solu*le *y stirrin% !it# a %lass rod

If t#e "reci"itate is solu*le) A%Br is

"resent in t#e solution0 Ot#er!ise) A%I is "resent0

RESULTS

 T#e fusion solutions o*tained from t#e t!o

com"ounds) "-c#loroaniline and sulfanilic acid) !ere su*ected to conrmatory tests and t#e o*tained data is s#o!n in t#e ta*le0

Sample Sulfur Test Nitrogen Test Haloge n Test "-c#loroaniline -   Sulfanilic acid  

- To test for t#e "resence of sulfur) sodium nitro"russide !as added to t#e fusion

solution0 Dee" *lue-(iolet coloration in t#e solution indicates t#e "resence of sulfur %i(en as.

Na₂Sn+ Na₂[Fe(CN)₅NO]  Na₄[Fe(CN)₅NOS]

(violet in olor)

 To test for t#e "resence of nitro%en) 9eSO_< !as added into t#e fusion solution %i(in% t#e follo!in% reaction.

2NaCN + FeSO₄  Fe(CN)₂ + Na₂SO₄ Fe(CN)₂ + 4NaCN  Na₂Fe(CN)_!

After!ards) addition of =9 !as done to intensify t#e *lue coloration of t#e solution0 9inally) 9eCl₃ !as added to form NaCl !#ic# is a *lue "reci"itate0

"Na₄Fe(CN)_! + 4 FeCl_"  Fe₄[Fe(CN)_!]₅

 Test for t#e "resence of #alides in(ol(es t#e addition of ?NO₃ to t#e solution and #eatin% if after!ards0 T#is is to e$"el ?CN or ?_:S in t#e sodium fusion0

Addition of sil(er nitrate 6A%NO₃7 into t#e sodium fusion resulted in t#e follo!in%

reactions.

NaCl_6a'7  A%NO_{3 6a'7} F A%Cl_6s7  NaNO_{3 6a'7}

6!#ite "reci"itate7

NaBr_6a'7  A%NO_{3 6a'7} F A%Br_6s7  NaNO_{3 6a'7}

6"ale yello! "reci"itate7

NaI_6a'7  A%NO_{3 6a'7} F A%I_6s7  NaNO_{3 6a'7}

6yello! "reci"itate7

,-c#loroaniline

- Git# a formula of ClC_>?_<N?_:

- It can *e noted t#at only nitro%en and c#lorine) a #alo%en) are "resent in t#e com"ound) indicatin% a ne%ati(e result for t#e sulfur test

Sample Sulfu r Test Nitro gen Test Halog en Test "-c#loroa niline -   Sulfanili c acid  

-Sulfanilic acid

- Git# a formula of C_>?_HNO₃S

- It can *e o*ser(ed t#at t#ere is no #alo%en in sulfanilic acid) *ut t#e

"resence of sulfur and nitro%en are conrmed Sample Sulfu r Test Nitro gen Test Halog en Test "-c#loroa niline -   Sulfanili c acid  

-CONCLUSION

Sodium fusion is a test to determine t#e "resence of some elements lie sulfur) nitro%en) and #alides suc# as c#lorine) *romine) and iodine0 T#is is "ossi*le *y turnin% t#ese insolu*le elements into

solu$le so%ium salts&

 T#e "resences of t#e mentioned elements are determined t#rou%# series of

'ualitati(e tests mainly *y forming olore% preipitates or pro%uts0

9lame test can also *e done as a "retest for #alo%en since a %reen 1ame result indicates t#e "resence of #alo%ens0

RECOMMENDATION

Since t#e e$"eriment em"loyed only one conrmatory test for t#e "resence of

nitro%en) sulfur) and #alo%ens) it is

recommended to use ot'er met'o%s for conrmin% t#e elements mentioned0

ANSGERS TO @UIDE

8UESTIONS

& O*gen Ferrox Test 

-@rind one crystal of ferric ammonium

sulfate and a crystal of "otassium cyanate usin% a %lass rod 6do t#is in a dry s"ot

"late7

-Add : dro"s of t#e unno!n in a se"arate !ell

-Use t#e %lass rod !it# attac#ed %round u" crystals to stir t#e unno!n

,& -'osp'orus

-T#e unno!n is fused !it# sodium "ero$ide 6Na_:O_:7

-,#os"#orus "resent in t#e unno!n is con(erted to sodium "#os"#ate

-9used mass is e$tracted !it# !ater -A'ueous e$tract is #eated !it#

concentrated nitric acid and ammonium moly*ate solution0

- .ello/ preipitate of ammonium p'osp'omol*$ate (NH_")_"[-0o_#2O₄₁]

:0 Discuss ot#er met#ods of detectin% t#e "resence of sulfur) nitro%en and #alo%en in or%anic com"ounds0

& Sulfur

Using the sodium fusion solution

Lead acetate solution is added to t#e

fusion solution0 A "ositi(e test for sulfur is indicated *y t#e "resence of a $la

preipitate (-$S)& Oxidation test

 T#e unno!n or%anic com"ound is #eated !it# o$idi/in% fusion mi$ture 6Na_:CO₃ 

=NO₃70 If sulfur is "resent) it !ill *e

o$idi/ed to sulfate0 T#e fused mass is

,& Nitrogen

 Addition of p-nitrobenzaldehyde

 To t#e fusion solution) add

"-nitro*en/alde#yde solution0 After!ards)

add a *asic solution of o-dinitro*en/ene0 A "ositi(e test is indicated *y a $lueviolet olor0

Oxidation of benzidine with cupric ion

 T#is reaction !ill not tae "lace in t#e a*sence of cyanide ion0 T#e cyanide com"le$es !it# cu"rous ions so as to increase t#e o$idation "otential of t#e system0

C& Halogens

Sodium odide in Acetone Test 

 To t#e unno!n) add solution of sodium iodide in acetone0 S#ae tu*e to

ade'uately mi$ t#e unno!n and t#e solution0 If a*out 4 minutes #as "assed and "resence of "reci"itate is still not e(ident) "lace test tu*e in a 42 !ater *at#0 9ormation of a /'ite preipitate

indicates "resence of #alides0

!eilstein Test 

?eat t#e ti" of a co""er !ire in a *urner

1ame0 Cool t#e !ire sli%#tly t#en di" it into t#e unno!n0 ?eat it once a%ain0 A green 3as' is indicati(e of c#lorine) *romine)

RE9ERENCES

Sri(asta(a) A0=0) 6:22H70 "hemistry 0 Del#i. J0=0 6India7 Enter"rises

"hemical Tests for Un#nowns$ Retrie(ed from

#tt".KKcactus0di$ie0eduKsm*lacKc#emla*sKC#emicalTest sforUnno!ns0"df 

%etection of &hosphorus' Sulfur and Oxygen Retrie(ed from

#tt".KK%radestac0comKClass-55t#-Science-Git#-Mat#-KDe tection-of-,#os"#orus-Sul"#ur-and-O$y%enK5H4>:-34><-: :H>-study-!t!

Organic (ualititati)e Analysis$ Retrie(ed from

#tt".KKfaculty0s!osu0eduK!illiam0ellyK"dfK'o:a0"df  Test for *alides$ Retrie(ed from

#tt".KKacademics0!ellesley0eduKC#emistryKc#em:55la*KOr% oLa*ManualKA""endi$KClassicationTestsK#alide0#tml